JP2013101008A - Treatment method and treatment device for radioactive cesium and radioactive strontium contained substance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and efficiently remove radioactive cesium and radioactive strontium from a substance such as soil or mud contaminated by the radioactive cesium and the radioactive strontium.SOLUTION: An organic substance from which cesium and strontium is selectively extractable is brought into contact with a substance containing radioactive cesium and radioactive strontium. Then, at least supercritical carbon dioxide is supplied to and brought into contact with at least the organic substance, and the organic substance is dissolved in the supercritical carbon dioxide. Then, the supercritical carbon dioxide is decompressed, and the supercritical carbon dioxide is converted into carbon dioxide gas so that the organic substance can be separated and removed from the supercritical carbon dioxide.

Description

  The present invention relates to a processing method and a processing apparatus for radioactive cesium and radioactive strontium-containing substances.

  For example, when a large-scale accident occurs at a nuclear power plant, there is a concern that a large amount of radionuclide will be scattered and cause soil contamination. Radioactive nuclides are also contained in sludge generated at sewage treatment plants in various regions and incineration ash generated at municipal waste incineration plants in various regions, and the development of treatment methods is urgently needed.

Most of the radionuclides contained in soil and sludge contaminated with radionuclides are ¹³⁴ Cs, ¹³⁷ Cs, and ⁹⁰ Sr. In particular, ¹³⁷ Cs has a half-life of 30.2 years, and ⁹⁰ Sr has a half-life of 28. It is expected to have a long-term impact of 7 years. Therefore, removal of cesium and strontium from contaminated soil and sludge is desired. Several proposals have been made for the removal of such radioactive contaminants.

  For example, after mixing pollutants including radioactive substances and chemical species such as cations and anions, a potential gradient is generated between the anode and the cathode, and these cations or anions are moved to the cathode and the anode, respectively. It has been proposed that a matrix material having an affinity for a radioactive substance is disposed and adsorbed, and the contaminants are precipitated by setting the pH of these systems to a predetermined value or less to remove the radioactive substance.

  In addition, at least one set of electrodes is embedded in the surface layer of the contaminated soil at a predetermined interval, and by energizing between these electrodes, the pollutants are accumulated at the electrodes, and a toxic substance highly accumulating plant is cultivated in the contaminated soil, A method for removing the pollutant by absorbing the plant is disclosed. However, these methods require electrode installation and energization, and are difficult to process on site. Moreover, since the process of plant cultivation is included, there also exists a problem that a process takes long time.

  In addition, methods using environmentally friendly synthetic inorganic ion adsorbents and inorganic arsenic adsorbents have also been proposed. This method can be used for the production of land water such as oceans, rivers, lakes, and groundwater, and agricultural chemicals, alloys, and semiconductors. Although it is useful for separation and removal of wastewater, there is a problem that the adsorbent used for adsorption cannot be removed in soil and sludge.

  In addition, methods for removing radionuclides from contaminated water and soil using lichens, their metabolites and synthetic metabolites have also been proposed, but the target nuclides are uranium and plutonium, and cesium is removed. Not suitable for. In addition, a method has been proposed to deal with soluble heavy metal pollutants present in the formation or the seafloor, but by stabilizing it, the heavy metal pollutants are prevented from being re-fluidized by groundwater. Cesium and strontium Is not intended to remove.

Japanese Patent No. 4128620 JP 2007-289897 Japanese Patent No. 3557461 JP 2002-1047489 A JP-A-6-39055 JP-A-6-23340

  An object of the present invention is to easily and efficiently remove radioactive cesium and radioactive strontium from substances such as soil and sludge contaminated with radioactive cesium and radioactive strontium.

  One embodiment of the present invention includes a step of bringing a substance containing radioactive cesium and radioactive strontium into contact with an organic substance capable of selectively extracting cesium and strontium, supplying supercritical carbon dioxide to at least the organic substance, and Contacting the organic matter with the supercritical carbon dioxide, depressurizing the supercritical carbon dioxide, and converting the supercritical carbon dioxide into carbon dioxide gas, thereby converting the organic matter from the supercritical carbon dioxide. A method for treating radioactive cesium and radioactive strontium-containing materials, comprising the steps of: separating and removing.

  According to the present invention, radioactive cesium and radioactive strontium can be easily and efficiently removed from substances such as soil and sludge contaminated with radioactive cesium and radioactive strontium.

It is a figure which shows schematic structure of the processing apparatus of the radioactive cesium and radioactive strontium containing substance of embodiment.

  FIG. 1 is a diagram showing a schematic configuration of a processing apparatus for radioactive cesium and radioactive strontium-containing materials according to the present embodiment.

  As shown in FIG. 1, a processing apparatus 10 for radioactive cesium and radioactive strontium-containing material according to the present embodiment includes a high-pressure processing tank 11 and supercritical carbon dioxide connected to the high-pressure processing tank 11 via pipes 22 and 23. It has a supply device 12, a decompressor 13 connected to the high-pressure treatment tank 11 via a pipe 24, and a separation / recovery tank 14 connected to the decompressor 13 via a pipe 25. As will be described below, the decompressor 13 and the separation / recovery tank 14 constitute a separation / recovery device for separating and recovering organic substances from supercritical carbon dioxide containing organic substances.

  A heat exchanger 15 is disposed between the high-pressure treatment tank 11 and the supercritical carbon dioxide supplier 12 via pipes 22 and 23. Further, the high-pressure treatment tank 11 is disposed in a constant temperature bath 16 maintained at a temperature equal to or higher than the critical temperature of carbon dioxide, and the separation and recovery tank 14 is also stored in a constant temperature bath 17 maintained at a temperature equal to or higher than the critical temperature of carbon dioxide. Is arranged. As will be described below, the heat exchanger 15 and the thermostatic chambers 16 and 17 are provided for easily obtaining and retaining supercritical carbon dioxide, and are not essential requirements of the present embodiment.

  The main constituent elements such as the high-pressure treatment tank 11 and the supercritical carbon dioxide supply device 12 of the processing apparatus 10 shown in FIG. 1 and the constituent elements such as the pipe 21 are made of stainless steel such as SUS, which is rich in corrosion resistance and pressure resistance. be able to.

  Next, the processing method of the radioactive cesium and radioactive strontium containing substance using the processing apparatus 10 shown in FIG. 1 is demonstrated.

  First, radioactive cesium and radioactive strontium-containing material S1 is placed in the high-pressure treatment tank 11 shown in FIG. 1, and cesium and strontium are selectively selected from the material S1 so as to come into contact with the material S1 on the material S1. The organic substance S2 that can be extracted is added to In FIG. 1, the substance S1 and the organic substance S2 are shown separately, but depending on the type and aspect (form and size, etc.) of the substance S1, and the kind and aspect (form and size, etc.) of the organic substance S2. In some cases, the substance S1 and the organic substance S2 are mixed with each other.

  Examples of the substance S1 include any substance that may contain radioactive cesium and radioactive strontium, and examples thereof include soil, sludge, sand, rock, clay, concrete, and asphalt.

  In this case, when the substance S1 is soil, sludge, sand, etc., these are aggregates of particles, and the particles themselves are in the order of μm to cm, so that the contact area with the organic matter S2 is increased. Further, depending on the type of the organic substance S2, the substance S1 and the organic substance S2 can be mixed to further increase the contact area with each other.

  On the other hand, when the substance S1 is rock, clay, concrete, asphalt or the like, generally, it exists as a lump of a predetermined size in general. Therefore, when the substance S1 is a rock or the like, the above order of μm to the order of cm is used. It is preferable to pulverize as appropriate so that the size becomes. Thereby, the contact area with the organic matter S2 can be increased.

  In addition, a dispersion medium can be added to the high-pressure treatment tank 11 as necessary so as to increase the contact ratio between the substance S1 and the organic substance S2. In this case, since the substance S1 and the organic substance S2 come to flow in the dispersion medium, the contact area between them can be increased. However, when the substance S1 is sludge or the like and contains sufficient moisture, the moisture functions as the dispersion medium described above, and even when the organic substance S2 is liquid, the organic substance S2 itself functions as a dispersion medium. Even if a simple dispersion medium is not used, the substance S1 and the organic substance S2 can flow in moisture or the like, and the contact area between them can be increased.

  Examples of the dispersion medium include water, acetic acid, methanol, ethanol, n-propanol, isopropanol, acetone, and tetrahydrofuran.

  By bringing the substance S1 into contact with the organic substance S2 in the high-pressure treatment tank 11, cesium and strontium in the substance S1 are selectively extracted by the organic substance S2 and transferred into the organic substance S2. As a result, the organic substance S2 contains at least a part of radioactive cesium and radioactive strontium contained in the substance S1.

  Examples of the organic substance S2 that selectively extracts cesium include dioctyloxo-calix [4] -crown-6 and derivatives thereof.

Examples of the organic substance S2 that selectively extracts strontium include crown ether compounds (D-tBuCH ₁₈ C ₆ , D-tHexCH ₁₈ C ₆ ).

  Next, the valve 31 is opened, and carbon dioxide is introduced into the supercritical carbon dioxide supplier 12 from an external carbon dioxide supply source (not shown). In the supercritical carbon dioxide supplier 12, the introduced carbon dioxide is heated to a temperature of about 31 ° C. or higher and pressurized to a pressure of 7.3 MPa or higher to generate supercritical carbon dioxide G.

  Supercritical carbon dioxide G has characteristics of gas and liquid and is highly soluble. Therefore, various organic substances can be dissolved. In addition, since the viscosity is low, handling is easy, and if carbon dioxide is in a state slightly higher than room temperature, it can be generated only by pressure load, so the generation is easy and the viscosity is low as described above. In combination with this, control is easy.

  Although supercritical water may be used instead of supercritical carbon dioxide G, an atmosphere having a temperature of 374 ° C. or higher and a pressure of 22 MPa or higher needs to be formed in order to obtain supercritical water. However, in order to form such a high temperature and high pressure atmosphere, the apparatus becomes complicated and high strength is required for the entire apparatus. Therefore, the apparatus becomes expensive and handling is complicated. Therefore, if supercritical water is used to treat the radioactive cesium and radioactive strontium-containing material S1 as in this embodiment, the processing operation is erroneous, and the radioactive cesium and radioactive strontium-containing material S1 is contained in the high-pressure treatment tank 11. May leak into the atmosphere and contaminate the atmosphere with radioactivity.

  In addition, hydrocarbon gases such as ethane, propane, ethylene, and propylene can be brought into a supercritical state under conditions similar to those of carbon dioxide described above. However, since these hydrocarbon gases are flammable gases, they are not easy to handle. If an attempt is made to treat radioactive cesium and radioactive strontium-containing substance S1 as in this embodiment, the treatment operation is mistakenly caused by hydrocarbons. There is a risk of exploding gas. In this case, radioactive cesium and radioactive strontium-containing substance S1 leaks out into the atmosphere from the high-pressure treatment tank 11 or the pipe 23, and the atmosphere is contaminated with radioactivity. There is.

  Therefore, in the processing method of this embodiment, supercritical carbon dioxide G that is easy to generate and handle is used.

  The supercritical carbon dioxide G generated by the supercritical carbon dioxide supply device 12 is introduced into the heat exchanger 15 via the pipe 22, and the temperature of the supercritical carbon dioxide G does not become 31 ° C. or less and the pressure does not become 7.3 MPa or less. Thus, the supercritical state is maintained. Next, the supercritical carbon dioxide G is introduced into the high-pressure treatment tank 11 through the pipe 23.

  When the supercritical carbon dioxide G generated by the supercritical carbon dioxide supply device 12 can maintain a sufficiently high temperature before being introduced into the high-pressure treatment tank 11, the heat exchanger 15 is omitted, The supercritical carbon dioxide G can be directly introduced into the high-pressure treatment tank 11 from the supercritical carbon dioxide supply device 12.

  When the supercritical carbon dioxide G is introduced into the high-pressure treatment tank 11, the supercritical carbon dioxide G dissolves the organic substance S2 containing radioactive cesium and radioactive strontium.

  In the present embodiment, the high-pressure treatment tank 11 is disposed in the thermostatic tank 16, and maintains the supercritical state so that the temperature of the supercritical carbon dioxide G does not become 31 ° C. or lower. However, in the case where the temperature of the supercritical carbon dioxide G is sufficiently high and the supercritical state can be maintained when the organic matter S2 is dissolved in the high-pressure treatment tank 11, the thermostat 16 is omitted and the thermostat 16 is used. The heating operation can be omitted.

  The supercritical carbon dioxide G in which the organic substance S2 is dissolved is introduced into the decompressor 13 through the pipe 24. Since the atmospheric pressure is maintained at a pressure less than 7.3 MPa in the decompressor 13, the supercritical carbon dioxide G is converted into carbon dioxide gas. Thereby, the organic substance S2 contained in the supercritical carbon dioxide G is separated from the supercritical carbon dioxide G.

  The carbon dioxide gas converted from the supercritical carbon dioxide G and the organic matter S2 separated from the supercritical carbon dioxide G are sent to the separation and recovery tank 14. The carbon dioxide gas is released from the pipe 26 to the outside of the processing apparatus 10 with the valve 32 opened. Further, the organic substance S2 is released from the pipe 27 to the outside of the processing apparatus 10 with the valve 33 opened, and subjected to volume reduction or the like as necessary, and then subjected to cement solidification or glass solidification.

  Note that the organic substance S2 may include a part of the substance S1, but as described above, after being released to the outside of the processing apparatus 10, the substance S1 is used for cement solidification or glass solidification. No radioactive cesium or radioactive strontium leaks into the atmosphere and is contaminated.

  The carbon dioxide gas generated as described above is recovered without being discharged to the outside of the processing apparatus 10, transferred to the supercritical carbon dioxide supply device 12 through the pipe 28, and converted into supercritical carbon dioxide G again. be able to. As a result, carbon dioxide, which is a raw material gas for the supercritical carbon dioxide G, can be efficiently used, and the recent demand for energy saving can be satisfied.

  The supercritical carbon dioxide G generated in this way is also introduced into the high-pressure treatment tank 11 as described above to dissolve the organic matter S2 containing radioactive cesium and radioactive strontium, and further, the decompressor 13 and the separation and recovery tank. It is transferred to a separation and recovery device consisting of 14 and processed.

  In the present embodiment, the separation / recovery tank 14 is disposed in the thermostatic tank 17, and the generated carbon dioxide is heated to a predetermined temperature to generate the supercritical carbon dioxide G in the supercritical carbon dioxide supplier 12. In this embodiment, since the heat exchanger 15 is disposed between the high-pressure treatment tank 11 and the supercritical carbon dioxide supplier 12, the constant temperature bath 17 is omitted and the heating operation described above is also performed. Can be omitted.

  As mentioned above, although several embodiment of this invention was described, these embodiment was posted as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 10 Processing apparatus of radioactive cesium and radioactive strontium containing substance 11 Tank 12 Supercritical carbon dioxide supply device 13 Depressurizer 14 Separation recovery tank 15 Heat exchanger 16,17 Thermostatic bath S1 Radioactive cesium and radioactive strontium containing substance S2 Select cesium and strontium Extractable organic matter G Supercritical carbon dioxide

Claims (4)

Contacting an organic substance capable of selectively extracting cesium and strontium with a substance containing radioactive cesium and radioactive strontium;
Supplying and contacting at least supercritical carbon dioxide with respect to the organic substance, and dissolving the organic substance in the supercritical carbon dioxide;
Separating and removing the organic matter from the supercritical carbon dioxide by depressurizing the supercritical carbon dioxide and converting the supercritical carbon dioxide to carbon dioxide gas;
A method for treating radioactive cesium and radioactive strontium-containing materials, comprising:   Recovering the carbon dioxide gas, converting it to supercritical carbon dioxide, supplying and contacting the supercritical carbon dioxide with respect to at least the organic substance, and dissolving the organic substance in the supercritical carbon dioxide. The processing method of the radioactive cesium and radioactive strontium containing material of Claim 1 characterized by the above-mentioned. A tank for contacting an organic substance capable of selectively extracting cesium and strontium with a substance containing radioactive cesium and radioactive strontium;
A supercritical carbon dioxide supplier for producing and supplying supercritical carbon dioxide into the tank, bringing the supercritical carbon dioxide into contact with at least the organic matter, and dissolving the organic matter in the supercritical carbon dioxide; ,
A separation and recovery device for reducing the pressure of supercritical carbon dioxide containing the organic matter, converting the supercritical carbon dioxide into carbon dioxide gas, and separating and recovering the organic matter from the supercritical carbon dioxide;
An apparatus for treating radioactive cesium and radioactive strontium-containing materials, comprising:   The separation and recovery device is configured to transfer the carbon dioxide gas to the supercritical carbon dioxide supply device and to reuse the carbon dioxide gas as the supercritical carbon dioxide. 3. The processing apparatus of radioactive cesium and radioactive strontium containing material of 3.

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