JP2014085330A - Method for reducing radioactive cesium in incineration ash and method for storing water containing radioactive cesium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for reducing radioactive cesium from incineration ash containing radioactive cesium, and also to provide a method for safely storing water containing radioactive cesium.SOLUTION: A method for reducing radioactive cesium contained in incineration ash puts incineration ash containing radioactive cesium into an extraction container and stores water in a heating container, in an apparatus in which the heating container is placed in a bottom part, the extraction container is placed in a middle part, and a condenser is placed in an uppermost part. Then, the method repeats the steps of: (A) heating the heating container to generate moisture vapor; (B) cooling the moisture vapor in the condenser to generate condensed water; (C) feeding the condensed water into the extraction container; (D) discharging water into the heating container when it accumulates up to a predetermined level in the extraction container; and (E) accumulating the water in a state where radioactive cesium is dissolved in the water. A method for storing water containing radioactive cesium lets water containing radioactive cesium be absorbed in a high water-absorbing material and be filled in a storage container with the water in a solid phase state.

Description

  The present invention relates to a method for reducing radioactive cesium contained in incineration ash of incinerated materials generated in an environment contaminated with radioactive cesium and a method for storing water containing radioactive cesium.

  Due to the accident at the Fukushima Daiichi Nuclear Power Plant, a large amount of radioactive material was scattered not only in Fukushima Prefecture but also in the surrounding areas. Incinerators that incinerate domestic garbage and debris in those areas emit incineration ash containing high concentrations of radioactive cesium, but there is no subsequent proper treatment method, and the incineration ash is filled into bags and the living environment It is expected that it will continue to increase in the future. Cesium 137 has a half-life of 30 years, cesium 134 is 2 years, and there are concerns about the effects on the human body. It is important for the region to reduce the volume of incinerated ash containing these radioactive cesiums or eliminate them from the living environment. It is an urgent issue. The situation where radioactive materials are scattered is impossible from the outset, and it can be said that there has been almost no development of technology that assumes such a situation. At the Fukushima Daiichi nuclear power plant where the accident occurred, adsorbents that adsorbed radioactive cesium and the like from a large amount of contaminated water were packed in containers and stored on the site of the nuclear power plant. Although the adsorbent is presumed to be zeolitic, the cesium adsorption rate of the zeolitic adsorbent is low, and volume reduction of the adsorbent is desired by improving the adsorption rate.

  Patent documents related to cesium include the following. Patent Document 1 is a method for efficiently extracting cesium from a cesium ore containing rubidium using an organic solvent.

  In Patent Document 2, an organism that has taken in a radioactive material from the environment is pulverized to the cellular level by blasting, the radioactive material exposed on the surface of the fine powder is dissolved in water, and the radioactive material in the water is further adsorbed by an adsorbent It is a method to make it.

  In Patent Document 3, cesium dissolved in water is adsorbed on a Prussian blue type adsorbent, and then applied to the adsorbent to recover cesium that is desorbed.

  Patent Document 4 relates to a method for solidifying radioactive waste, in which radioactive solid waste is mixed with molten glass and contained in glass, and then vitrified again using glass agents having different compositions.

  Patent document 5 is related with the solidification method which solidifies a radioactive substance using solidification materials, such as blast furnace slag and Portland cement.

JP-A-5-5134 Japanese Patent No. 5018989 JP 2011-200856 A Japanese Patent Laid-Open No. 9-72998 JP-A-9-212194

  The first object of the present invention is to reduce radioactive cesium from incineration ash so that the incineration ash can be safely returned to the living environment. The second object of the present invention is to store the radioactive cesium removed from the incineration ash safely so as not to affect the living environment.

As a result of intensive studies on the above problems, the present inventors have completed the following invention. In the first aspect of the invention, a heating vessel equipped with a heater and capable of containing water is disposed at the bottom, and an extraction vessel equipped with a filter medium capable of containing incinerated ash containing radioactive cesium and capable of containing water is arranged in the middle portion. A condenser that cools and condenses the water vapor is disposed at the top, the condenser condenses the water vapor generated in the heating container, and the condensed water generated in the condenser flows into the extraction container. In the apparatus configured to be supplied and the water in the extraction container is supplied to the heating container via the filter medium, incineration ash containing radioactive cesium is charged into the extraction container, and water is supplied to the heating container. After storage
(A) heating the heating container to generate water vapor;
(B) The water vapor is cooled by the condenser to generate condensed water,
(C) supplying the condensed water to the extraction container;
(D) When a certain amount of water has accumulated in the extraction container, the water is discharged into a heating container;
(E) accumulate radioactive cesium in the heating vessel in a state dissolved in water;
It is a method for reducing radioactive cesium contained in incinerated ash, characterized by repeating the process.
The invention according to claim 2 is the method for reducing radioactive cesium contained in the incinerated ash according to claim 1, wherein the incinerated ash is a 60-mesh sieve.
The invention according to claim 3 is provided in the incineration ash according to claim 1, further comprising a discharge means for discharging the water vapor generated in the heating container or the condensed water of the condenser to the outside of the apparatus. This is a method for reducing radioactive cesium.
The invention according to claim 4 is a method for storing water containing radioactive cesium, characterized in that the water containing radioactive cesium is absorbed by a highly water-absorbing material and filled in a container in a solid state.
The invention according to claim 5 is the method for storing water containing radioactive cesium according to claim 4, wherein the water containing radioactive cesium is water accumulated in the heating container.

  Generally, incineration ash contains alkaline metals such as sodium, potassium, calcium and the like, and when the incineration ash is extracted with water, the extracted water shows high alkalinity. Since radioactive cesium is a metal that exhibits alkalinity when dissolved in water, it is difficult to extract to the water side when the pH of the extracted water is high. According to the invention of claim 1, since the water supplied to the extraction container is evaporated water from the heating container, it does not contain impurities such as sodium, potassium, calcium, etc., and has a neutral pH and does not contain radioactive cesium. It has the effect of efficiently extracting radioactive cesium from the incineration ash to the water side so that the incineration ash can be freely treated in the living environment.

  Incineration ash includes main ash that is incineration residue remaining at the bottom of the incinerator and fly ash that is captured by a dust collector accompanying the combustion gas. Further, in the case of a small-scale incinerator without a dust collector, fly ash is not generated, and pseudo main ash that is an incineration residue is generated. In either case, the incineration ash is often refined rather than the original incinerated product. However, incineration ash may be solidified by being piled up in the field or packed in bags and stored in multiple stages. The invention according to claim 2 is characterized in that not only the incineration ash discharged from the furnace but also a solidified incineration ash including those refined by means such as pulverization are used under a 60 mesh sieve. Yes. The invention according to claim 2 has an effect that radioactive cesium is easily extracted into water by using incinerated ash that has been refined.

  According to the invention which concerns on Claim 3, it has the effect that the density | concentration of the radioactive cesium in the water of a heating container can be adjusted by discharging | emitting the water vapor | steam which generate | occur | produced in the heating container, or the condensed water of a condenser outside the said apparatus. By discharging water vapor or condensed water out of the system, the concentration of radioactive cesium in the water in the heating vessel increases, and the volume of water containing radioactive cesium to be stored can be freely reduced. In addition, the ability to freely adjust the concentration of radioactive cesium in water also has the effect of expanding the range of adaptation to a subsequent method for treating water containing radioactive cesium.

  According to the inventions according to claims 1 to 3, it is excellent in the convenience of subsequent handling in that a substance containing radioactive cesium can be handled in a liquid state. For example, it can be transferred from the heating container liquid discharge valve (24) of the heating container 1 of FIG. 1 to the square storage container 18 of FIG. 2 or the flexible container storage container 20 of FIG. . It is important that processes that handle radioactive materials be unmanned as much as possible.

  According to the fourth aspect of the present invention, the water containing radioactive cesium is stored in a container in a solid phase with a superabsorbent. The solid phase state refers to the state of the solid phase when the state of the substance is divided into three states, gas phase, liquid phase, and solid phase. The solid phase includes a gel state. When water containing radioactive cesium is stored in a container as it is, when the container deteriorates, water containing radioactive cesium flows out of the container and causes environmental pollution. According to the invention of claim 4, the water is in a solid phase. There exists an effect that the outflow outside a container can be prevented by being in a state.

  Since water has the property of shielding radiation, radioactive cesium in water has a lower air dose (microsievert value) than cesium in solids of the same concentration (becquerel / kg). It has the effect that the influence on is reduced.

  According to a fifth aspect of the present invention, the water containing radioactive cesium is stored in the container in a solid state by using a superabsorbent in the water stored in the heating container according to the first or third aspect, and the container has deteriorated. In this case, the water containing radioactive cesium is prevented from flowing out of the container and causing environmental pollution. Further, in the present invention, since the concentration of radioactive cesium can be increased freely, the volume can be reduced as compared with the case where a radioactive substance as described in Patent Document 4 or Patent Document 5 is solidified with cement or glass. It can be said that this is far superior to the conventional method.

Schematic diagram of radioactive cesium extraction equipment for incineration ash Side cross-sectional view of a storage container with radioactive cesium-containing water in a superabsorbent and stored in a rectangular storage container Side sectional view of a storage container in a state where water containing radioactive cesium is contained in a superabsorbent and stored in a flexible container type storage container

The present invention will be described in detail below.
Cesium is an alkali metal and basically has a property of dissolving in water, but in a naturally scattered state such as soil, it is intricately entangled with other elements and does not easily dissolve in water. However, cesium is cesium oxide, cesium carbonate, cesium hydroxide, or cesium chloride when exposed to chlorine compounds contained in incinerators such as oxygen, carbon dioxide, or household waste, such as incinerated ash. It will start to dissolve in water. In addition, since the incineration object loses its original shape in the incinerator and is pulverized, radioactive cesium is likely to elute into water when it comes into contact with water. The present invention pays attention to such properties of incinerated ash and is effectively used.

  The outline of the radioactive cesium removal of the present invention is as follows. The condensed water generated by heating the heating vessel to generate water vapor and sending the water vapor to the uppermost cooling pipe is supplied to the extraction vessel and comes into contact with the incineration ash to dissolve the radioactive cesium in the incineration ash, Return to the heating vessel via the filter media. The water condensed by the condenser does not contain alkaline metals such as sodium, potassium and calcium, and does not contain radioactive cesium, so that radioactive cesium can be extracted efficiently. Since radioactive cesium has a boiling point much higher than that of water and does not evaporate, it remains in the heating vessel. Therefore, by repeating the above cycle, radioactive cesium is concentrated in the heating vessel.

  A heating container is a container with a jacket that can supply a high-temperature heat medium (oil or high-pressure steam) to the outside, a pipe that circulates the heat medium inside the container, a thing that has an electric heating coil, Any type can be used as long as it can indirectly heat the water in the heating vessel, such as one using ultrasonic waves.

  Since the water supplied to the extractor of the present invention is obtained by condensing water evaporating from the heating container, it does not contain radioactive cesium having a boiling point much higher than that of water. The extraction capacity of cesium is kept high. In addition, when this water accumulates enough to immerse the entire amount of incinerated ash contained in a certain amount in the extraction container, the water is discharged to the heating container through the furnace material of the extraction container, so the total amount of incinerated ash is Washed with water all over. The water can be discharged via an automatic open / close valve linked to the liquid level of the extraction container, or when the liquid level in the extraction container reaches a certain level using the siphon principle, the liquid in the extraction container is discharged. May be a system that repeats discharging at a time.

  The condenser of the present invention indirectly cools the water vapor evaporated from the heating vessel with water. The condensed water is supplied to an extractor, and radioactive cesium is extracted from the incineration ash. At this time, the higher the temperature of the condensed water, the easier it is to extract radioactive cesium in the incineration ash. Therefore, it is desirable that the condenser is configured so that the temperature of the condensed water can be adjusted.

  The “Special Measures for Radioactive Substance Contamination Targets” established by the Ministry of the Environment describes precautions regarding a method for treating waste containing radioactive substances exceeding 8000 Bq / kg. In addition, “Guidelines for the prevention of radiation hazards for workers engaged in decontamination work” established by the Ministry of Health, Labor and Welfare include points to be noted by workers who handle waste containing radioactive materials of 10,000 becquerel / kg or more. Have been described. This invention can adjust the density | concentration of the radioactive cesium contained in the water which should be stored corresponding to those legal standards suitably. For example, when the entire apparatus of the present invention is unmanned by automation or the entire apparatus is completely shielded, the concentration of radioactive cesium is concentrated to a concentration exceeding 10,000 Bq / kg and contains radioactive cesium. It is possible to reduce the volume of water freely. If the radioactive cesium concentration in the water in the heating container needs to be 10,000 Bq / kg or less in consideration of the health of the worker, the purpose is to adjust the input amount of water to the heater in the present invention. Can be diluted to a concentration of

  Since water has a property of shielding radiation, radioactive cesium in water has a lower air dose (microsievert value) than cesium in solids of the same concentration (becquerel / kg: Bq / kg), so it has an effect on the human body. Is small. Therefore, at the same concentration (Bq / kg), radioactive cesium dissolved in water is less affected by radiation than the solid adsorbent adsorbed with radioactive cesium.

  As the solids become finer, the surface area becomes larger, and the radioactive cesium contained therein is easily extracted into water. Therefore, the smaller the particle size of the incinerated ash treated in the inventions of claims 1 to 3 of the present invention, It is preferably 60 mesh or less, and more preferably 100 mesh or less.

  In order to reduce the volume of water containing radioactive cesium, it is preferable that the superabsorbent absorbs at least the same amount of water as its own weight. Preferably, it absorbs water at least 10 times its own weight, more preferably at least 100 times its own weight. Examples of the water-absorbing agent 10 times or more of its own weight include acrylate resin, polyamino acid resin, and cellulose resin. Acrylates have low biodegradability and polyamino acids and celluloses have high biodegradability. The acrylate and polyamino acid systems have a high water absorption capacity, but the cellulose system is slightly low. Since the storage of water containing radioactive cesium lasts for a long period of time, in the inventions of claims 4 and 5, it is preferable to use an acrylate-based superabsorbent having a low biodegradability and a high water absorption capacity. Moreover, when the salt content in incineration ash influences water absorption, a salt-resistant superabsorbent is preferable.

  The storage container is preferably made of a material that shields radiation. In particular, when water accumulated in the heating container is highly reduced in volume and radioactive cesium becomes several hundred thousand or several million Bq / kg, a shielding material is used to prevent radiation from leaking out of the storage container. A storage container is required.

  Hereinafter, the present invention will be described more specifically by way of examples.

The extraction apparatus shown in FIG. 1 was used. Extracted 23.2 g of incinerated ash (17) containing radioactive cesium 2780 Bq / kg ( ¹³⁴ Cs1030 + ¹³⁷ Cs1750) under 60 mesh sieve of ash taken from the bottom of a wood fuel incinerator (Tono Kosan Co., Ltd., Iwaki City) The cylindrical filter paper (6) of the machine (2) was filled and the upper part was covered with absorbent cotton. A heating vessel (1) having an internal volume of 200 ml was charged with 100 g of distilled water and a small amount of molecular sieve as zeolite. Distilled water (50 g) was placed in the cylindrical filter paper (6) of the extractor (2). The cooling water control valve (9) of the cooler (Allen type) 3 was fully opened to flow cooling water, and the power source (5) of the heater (4) (100 V, 500 W) was turned on. The water vapor evaporated from the heating container (2) was condensed in the condenser (3), the condensed water flowed into the extraction container, and when the extraction container (2) became full, the extraction liquid was discharged into the heating container at once. The temperature of the condensate (15) was 50 ° C. The state where water was refluxed between the heating vessel, the condenser and the extractor was continued for 24 hours, and then the heating vessel was turned off. After the heating container reached room temperature, the cylindrical filter paper (6) containing the incinerated ash in the extraction container (2) was taken out and dried in a dryer at 60 ° C. for 2 days until no weight loss could be confirmed. The weight after drying was 17.9 g, and the radioactive cesium concentration (Bq / kg) was 293 in total ( ¹³⁴ Cs116 + ¹³⁷ Cs177). The water in the heating vessel (1) was 90 ml, pH = 13.5, and the radioactive cesium concentration (Bq / kg) was 2902 ( ¹³⁴ Cs1091 + ¹³⁷ Cs1811).

Comparative Example 1

After injecting 23.5 g of incinerated ash and 150 g of distilled water used in Example 1 into a 300 ml eggplant type flask, a Dimroth type condenser was attached to the mouth of the eggplant type flask, and water was allowed to flow through the condenser. The eggplant-shaped flask is immersed in an oil bath, and while stirring the flask, the temperature of the oil bath is 130 to 140 ° C., the temperature of the liquid in the flask is 100 ° C., and water is refluxed between the flask and the cooler. The state was left for 24 hours. After cooling the flask, the slurry in the eggplant-shaped flask was filtered with a fold filter paper. The filtered ash was dried as in Example 1. The weight of the filtered ash after drying was 19.5 g, and the total concentration of radioactive cesium (Bq / kg) was 702 ( ¹³⁴ Cs269 + ¹³⁷ Cs433). The filtrate 106 ml, pH = 13.5, filtrate concentration of radioactive cesium (Bq / kg) was total ^{372 (134 Cs134 + 137 Cs238)} .

In Example 1, the state in which water is refluxed between the heating container, the condenser, and the extractor is continued for 24 hours, and then the water vapor discharge valve (18) is released, and the liquid level of the heating container (1) decreases. The heating container (1) was turned off. Others were the same as in Example 1. The weight of the extraction container (2) after taking out the incinerated ash and drying was 19.9 g, and the radioactive cesium concentration (Bq / kg) was 296 in total ( ¹³⁴ Cs111 + ¹³⁷ Cs171). The water in the heating vessel (1) was 50 mlg, pH = 13.6. The water of the heating vessel (1) is 20ml, pH = 13.6, concentration of radioactive cesium (Bq / kg) was ^{7255 (134 Cs2727 + 137 Cs4528)} .

(Comparative Example 2)
In Example 1, a 16-mesh screen of ash taken from the bottom of a wood-fueled incinerator (Iwaki Tono Kosan Co., Ltd.) (radioactive cesium concentration (Bq / kg): total 2631 ( ¹³⁴ Cs975 + ¹³⁷ Cs1656) Was used in accordance with Example 1 except that was used as incineration ash (17), the weight after taking out the incineration ash from the extractor (2) and drying was 22.2 g, and the radioactive cesium concentration (Bq / kg) was The total was 650 ( ¹³⁴ Cs257 + ¹³⁷ Cs393), and the water in the heating container (1) was 92 ml, and the radioactive cesium concentration (Bq / kg) was 389 ( ¹³⁴ Cs140 + ¹³⁷ Cs249).

  In a beaker containing 30 ml of water in the heating container (1) obtained in Example 1, 0.1 g of Sanyo Kasei's super water-absorbing agent Aqua Pearl SAP was added. After 30 minutes, the water became a gel and no water flowed out of the beaker.

(Summary of Examples and Comparative Examples)
From Example 1 and Comparative Example 1, even when the amount of incinerated ash used, the amount of water and the heating temperature (100 ° C.) were the same, the extraction rate of radioactive cesium in the incinerated ash was (1-17. 9 × 293 / 23.3 / 2780) × 100 = 91.2%, and in Comparative Example 2, (1−90 × 633 / 23.5 / 2780) × 100 = 78.6%, which is an example of the present invention. It is clear that one method is effective.

  In Example 2, the incinerated ash can be freely treated in the environment by reducing the radioactive cesium concentration from 2780 Bq / kg to 296 Bq / kg. The fact that the extracted water was 10 ml and the radioactive cesium concentration was 7255 Bq / kg was that the volume of incinerated ash about 47 ml (23.2 g: apparent specific gravity about 0.5) was reduced to 10 ml. The present invention 2 shows that the volume of incinerated ash can be freely reduced by evaporating water in the extract and concentrating radioactive cesium.

  Example 3 shows that a high-concentration radioactive cesium aqueous solution can be made into a solid phase by a superabsorbent. If radioactive cesium concentrated as an aqueous solution can be in a solid state, when it is stored in a radiation shielding container for a long period of time, even if the container deteriorates, water will not leak to the outside and will not cause environmental pollution. It is suitable as a storage method for cesium.

  According to the present invention, radioactive cesium in incineration ash is efficiently extracted into water, and the original incineration ash can be freely treated in a living environment. The water extracted from radioactive cesium can be reduced in volume by freely adjusting the concentration of radioactive cesium, and the extracted water can be stored in a container in a solid phase with a superabsorbent. Since it can be stored safely without leaking outside, it can be used in municipal waste incineration facilities.

1 Heating vessel 2 Extraction vessel 3 Condenser 4 Heater (heating coil)
5 Power supply 6 Filter cloth 7 Water evaporating pipe 8 Extract liquid discharge pipe 9 Cooling water amount adjusting valve 10 Water vapor 11 Water vapor 12 Cooling water inlet 13 Cooling water outlet 14 Atmospheric release 15 Condensed water 16 Water 17 Incinerated ash 18 Square storage container 19 High water absorption Water containing radioactive cesium in a solid phase with an agent 20 Flexible container bag-type storage container 21 Water containing radioactive cesium in a solid phase with a superabsorbent agent 22 Sealing port 23 of a flexible container bag-type storage container Steam discharge Valve 24 Heating vessel liquid discharge valve

Claims (5)

A heating vessel equipped with a heater and capable of containing water is arranged at the bottom, and an extraction vessel equipped with a filter medium capable of containing incinerated ash containing radioactive cesium and containing water is arranged in the middle part to cool and condense water vapor A condenser is arranged at the top, the condenser condenses water vapor generated in the heating container, and the condensed water generated in the condenser is supplied to the extraction container, and the water in the extraction container Is an apparatus configured to be supplied to the heating vessel via the filter medium, after injecting incinerated ash containing radioactive cesium into the extraction vessel, and storing water in the heating vessel,
(A) heating the heating container to generate water vapor;
(B) The water vapor is cooled by the condenser to generate condensed water,
(C) supplying the condensed water to the extraction container;
(D) When a certain amount of water has accumulated in the extraction container, the water is discharged into a heating container;
(E) accumulate radioactive cesium in the heating vessel in a state dissolved in water;
A method for reducing radioactive cesium contained in incinerated ash, characterized by repeating the process. The method for reducing radioactive cesium contained in incineration ash according to claim 1, wherein the incineration ash is under a 60-mesh sieve. The method for reducing radioactive cesium contained in incinerated ash according to claim 1, further comprising discharge means for discharging water vapor generated in the heating container or condensed water of the condenser to the outside of the apparatus. A method for storing water containing radioactive cesium, wherein water containing radioactive cesium is absorbed by a superabsorbent and filled in a storage container in a solid state. The method for storing water containing radioactive cesium according to claim 4, wherein the water containing radioactive cesium is water accumulated in the heating container.