JP6606132B2 - Radiocesium removal method and treatment facility - Google Patents

Description

  The present invention relates to a radioactive cesium removal method for removing radioactive cesium from an object to be treated by heat treatment.

  2. Description of the Related Art Conventionally, a technique is known in which radioactive cesium is volatilized by adding a radioactive cesium separation accelerator to a processing object containing radioactive cesium and subjecting it to heat treatment. For example, Patent Document 1 below discloses a technique for removing radioactive cesium from waste at a high removal rate by heating at a relatively low temperature by using a separation accelerator having a specific composition.

JP 2006-8963 A (published January 18, 2016)

  In the technique of Patent Document 1, the removal rate is high at an incineration temperature of 1100 ° C. However, at lower temperatures, water-soluble radioactive cesium remains in the treated products such as incineration ash and soil even at incineration temperatures exceeding 900 ° C., so it is necessary to wash the treated products with water after incineration. There is a problem that sometimes.

  In view of the above, an object of one embodiment of the present invention is to realize a method for removing radioactive cesium that can heat and volatilize most of radioactive cesium in a processing object at such a relatively low temperature.

  In order to solve the above-described problem, a method for removing radioactive cesium according to one embodiment of the present invention is a method for removing radioactive cesium that removes radioactive cesium from an object to be treated, and includes a combination of two or more chlorides. And a cesium separation accelerator containing a mixture or a double salt having a melting point lower than that of each chloride, and the amount of calcium contained is 5% in terms of calcium oxide concentration. % Or less, an addition step for obtaining a mixture of the separation accelerator and the treatment object, a heating step for heating the mixture at 900 ° C. or more and 1000 ° C. or less to volatilize radioactive cesium from the treatment object, The amount of water-soluble radioactive cesium in the treated product is the total radioactive cesium in the treated product among the radioactive cesium remaining in the treated product after the heating step. As the arm of the amount of 1/5 or less, and amount of the separation enhancing agent in the adding step, and a heating time in the heating step is set.

  Moreover, in order to solve said subject, the processing facility which concerns on 1 aspect of this invention is a processing facility which removes radioactive cesium from a process target object, Comprising: It consists of a combination of 2 or more types of chloride, and each A cesium separation accelerator containing a mixture or double salt having a melting point lower than that of a single chloride is added to the treatment object, and the amount of calcium contained is 5% by weight or less in terms of calcium oxide concentration. An addition device for obtaining a mixture of the separation accelerator and the processing object, and a heating furnace for heating the mixture at 900 ° C. to 1000 ° C. to volatilize radioactive cesium from the processing object, Of the radioactive cesium remaining in the processed product after heating in the heating furnace, the amount of water-soluble radioactive cesium in the processed product is 1/5 or less of the total amount of radioactive cesium in the processed product. In so that the amount of the separation accelerator the addition device is added, and the heating time of the heating furnace is set.

  According to one embodiment of the present invention, it is possible to heat and volatilize most of radioactive cesium in a processing object at a relatively low temperature of 900 ° C. or higher and 1000 ° C. or lower.

It is a figure which shows the flow of the process in the processing facility which concerns on one Embodiment of this invention. It is a figure which shows schematic structure of a processing facility. It is a figure which shows a composition and melting | fusing point of a low melting-point chloride. It is a phase diagram of a NaCl-CaCl _2. It is a figure which shows the composition of the waste which is a process target object in the Example and comparative example of this invention. It is a figure which shows a test condition and a test result.

  A method for removing radioactive cesium according to one aspect of the present invention is a method for removing radioactive cesium from a processing object, comprising a combination of two or more types of chlorides, and each comprising a single chloride. In addition, a cesium separation accelerator (hereinafter, simply referred to as a separation accelerator) containing a mixture or a double salt having a reduced melting point is added to the treatment object, and the amount of calcium contained is converted to a calcium oxide concentration. An addition step of obtaining a mixture of the separation accelerator and the treatment object, which is not more than% by weight; and a heating step of volatilizing radioactive cesium from the treatment object by heating the mixture at 900 ° C. or more and 1000 ° C. or less. ,including. Note that in one embodiment of the present invention, in addition to the heating step and the addition step, a washing step, a coprecipitation step, an adsorption step, a concentration step, a removal step, and a collection step may be included as necessary. Each step will be described later.

  Hereinafter, an embodiment of a method for removing radioactive cesium according to one embodiment of the present invention will be described. The treatment facility 100 according to the present embodiment reduces the radioactive cesium content of the treatment object by adding a separation accelerator to the treatment object containing radioactive cesium (Cs) and heat-treating the treatment object. It is a facility that reduces the volume. The treated product having a reduced radioactive cesium content can be used as a recycled resource.

[Flow of treatment at treatment facility]
With reference to FIG. 1, the flow of processing in the processing facility 100 will be described. FIG. 1 is a diagram illustrating a processing example in the processing facility 100.

(S1: crushing step)
The method for removing radioactive cesium according to one embodiment of the present invention may include a crushing step. A processing object such as decontamination waste, clean-up waste, and disaster waste containing radioactive cesium is transported to the processing facility 100 in the form of a package such as a flexible container. In the processing facility 100, first, a crushing process is performed to crush these processing objects. In this embodiment, since the processing target is a combustible material and it is assumed that it is incinerated, it can be said that the processing target is also an incineration target.

  The processing object may be soil, sewage sludge, or incinerated main ash or incinerated fly ash generated in a separate process, including radioactive cesium. Moreover, the said process target object may be the intermediate processed material to which radioactive cesium was concentrated obtained by removing beforehand the part (for example, sand, stone in the case of soil) which hardly contains radioactive cesium.

(S2: Addition step)
The method for removing radioactive cesium according to one embodiment of the present invention includes an addition step. In the addition step, a separation accelerator containing a mixture or a double salt containing two or more kinds of chlorides, each of which has a lower melting point than a single chloride, is added to the object to be treated. In the addition step, it is preferable that the addition amount of the separation accelerator is set so that the radioactive cesium remaining in the processed product after the heating step described later becomes substantially water-insoluble radioactive cesium. Note that the radioactive cesium remaining in the treated product becomes almost water-insoluble radioactive cesium, for example, out of the total radioactive cesium remaining in the treated product, the water-soluble radioactive cesium is 1/5 or less. Refers to that. Even if the addition amount of the separation accelerator is too small or too large, the remaining radioactive cesium does not become almost water-insoluble radioactive cesium. For this reason, for example, the treatment target is heated under different conditions with different amounts of addition of the separation accelerator, and the ratio of water-insoluble radioactive cesium in the radioactive cesium remaining in the treated product after the heating step is calculated, What is necessary is just to determine the addition amount of an appropriate separation accelerator.

  A separation accelerator is a substance that promotes the heat separation of radioactive cesium from a processing object containing radioactive cesium. The separation accelerator used in one embodiment of the present invention includes a low melting point chloride prepared using two or more types of chloride and having a melting point of 600 ° C. or lower. The separation accelerator only needs to contain at least the low melting point chloride as a chlorine source. Further, from the viewpoint of improving the removal rate of radioactive cesium from the object to be treated, it is preferable that the separation accelerator further contains a calcium source. More specifically, the separation accelerator is prepared such that the calcium concentration in the object to be treated after adding the separation accelerator is 5 wt% (weight%) or less in terms of CaO. Moreover, it is preferable that the calcium concentration is adjusted to be 1 to 2.5 wt% in terms of CaO. As the calcium source, for example, at least one of calcium chloride, slaked lime (calcium hydroxide), quick lime (calcium oxide), and calcium carbonate can be used.

Moreover, the amount of the chlorine source is preferably set such that the Cl concentration in the object to be treated after the separation accelerator is added is 0.9 wt% or more. More preferably, the amount of chlorine source is set to 1.5 wt%. As the chlorine source, low melting point chlorides containing chlorides such as calcium chloride and sodium chloride are suitable. For example, a mixture or double salt containing NaCl and CaCl ₂ and having a melting point of 600 ° C. or lower may be used as the separation accelerator. In this case, the melting point is preferably as low as 600 ° C. or lower. For example, a melting point of about 500 ° C. is preferably used. In the addition process of the present embodiment, a separation accelerator is added to the crushed processing object.

(S3: Incineration process)
The method for removing radioactive cesium according to one embodiment of the present invention includes a heating step. The heating step is a step of heating the processing object to which the separation accelerator is added and volatilizing radioactive cesium from the processing object. In the heating step, the mixture of the processing object and the separation accelerator is heated at a temperature of 900 ° C. or higher and 1000 ° C. or lower. In the heating step, it is preferable that the heating time is set so that the radioactive cesium remaining in the processed product after the heating step becomes substantially water-insoluble radioactive cesium. Specifically, the heating time is preferably 2 hours or more and 4 hours or less.

  In the present embodiment, the heating process is referred to as an incineration process. In the incineration process, the processing object to which the separation accelerator is added is incinerated. By incineration, radioactive cesium contained in the object to be treated is taken in as water-soluble cesium chloride (CsCl) into the incinerated main ash that is the object to be treated after the heating step. Most of the radioactive cesium incorporated as water-soluble CsCl in the incinerated main ash is chlorinated from the incinerated main ash and contained in the exhaust gas. The remaining radioactive cesium remains as partially water-soluble CsCl in the incineration main ash.

  The amount of separation accelerator added in S2 and the amount in S3 so that most of the radioactive cesium contained in the object to be treated is volatilized and the radioactive cesium remaining in the incinerated main ash becomes almost water-insoluble radioactive cesium. It is preferable that the incineration temperature and the incineration time are set. This makes it possible to dispose of the incinerated main ash generated in the incineration process without washing with water, or to recycle it after reducing the radioactive cesium concentration by melting without using water washing. Become. Since the water cleaning process is unnecessary, the drying process after the water cleaning process is also unnecessary, and the number of steps and the processing cost of the processing object are reduced. Moreover, it is preferable that the addition amount of the separation accelerator and the incineration time are set so that water-soluble radioactive cesium is 1500 Bq / kg or less among the radioactive cesium remaining in the processed product after the heating step. As a result of the study by the inventors of the present invention, the amount of the remaining water-soluble radioactive cesium increases when the amount of the separation accelerator added is too large, and the amount of the remaining water-soluble radioactive cesium decreases when the incineration time is lengthened. I know. For this reason, for example, the treatment object is heated, the amount of water-soluble radioactive cesium remaining in the treatment object after the heating step is measured, and if it exceeds 1500 Bq / kg, the addition amount of the separation accelerator is reduced, and incineration Applying at least one of increasing the time may be repeated. Thereby, the addition amount of the separation accelerator and the incineration time can be set so that the amount of water-soluble radioactive cesium remaining in the processed product after the heating step is 1500 Bq / kg or less.

(S4: Cooling step)
The method for removing radioactive cesium according to one embodiment of the present invention may include a cooling step. In the cooling step, exhaust gas discharged by incinerating the object to be treated is cooled. The configuration of cooling the exhaust gas may be performed with cooling water, may be configured with cooling air, or may be performed with a combination of cooling water and cooling air. By cooling the exhaust gas, gaseous salts such as CsCl contained in the exhaust gas become solid salts.

(S5: Release agent adding step)
The method for removing radioactive cesium according to one embodiment of the present invention may include a release agent adding step. In the release agent addition step, a release agent (filter aid) is added to the exhaust gas containing solid salts generated by cooling. This release agent facilitates reduction of pressure loss and removal of dust removal fly ash in the dust removal step described later.

(S6: First dust removal step)
The method for removing radioactive cesium according to one embodiment of the present invention may include a first dust removal step. In the first dust removal step, dusty solids are removed from the exhaust gas. Here, solid matters such as dust and cesium salt (CsCl) contained in the exhaust gas are collected as dust ash.

(S7: Fly ash cleaning process)
The method for removing radioactive cesium according to one embodiment of the present invention may include a cleaning step of cleaning a heat-treated product containing radioactive cesium volatilized from the object to be treated by heating with a cleaning liquid and removing the radioactive cesium from the heat-treated product. Good.

  Since the heat-treated product in the present embodiment is dust fly ash, in the present embodiment, the cleaning step is referred to as a fly ash cleaning step. In the fly ash cleaning process, the dust ash collected in S6 is cleaned with a cleaning liquid (for example, water). This dust removal fly ash contains a high concentration of cesium. For the cleaning, for example, a cleaning tank can be used. By washing, among the radioactive cesium in the dust ash, water-soluble and highly-eluting radioactive cesium (mainly CsCl) is transferred to the aqueous phase, thereby reducing the amount of radioactive cesium in the dust ash. It is known that 80 to 90% or more of the radioactive cesium can be removed from the dust ash by washing with water.

  Here, if the radioactive cesium concentration after cleaning is less than 8,000 (Bq / kg), which is the standard value of cesium concentration in landfilled waste as stipulated in the Special Measures against Radioactive Substance Contamination Countermeasures, The fly ash can be disposed of as it is. On the other hand, if the radioactive cesium concentration after washing exceeds the reference value, the volume is reduced by melting treatment, and the radioactive cesium concentration is further reduced. Note that the reference value is not limited to the above example, and it may be determined whether the disposal is performed as it is or the melting process is performed using a reference value according to laws and regulations or a disposal method. For example, a low standard value such as 100 (Bq / kg) defined in the clearance standard based on the Nuclear Regulation Law may be used as a standard for safely reusing waste.

(S8: Coprecipitation process)
In the method for removing radioactive cesium according to one embodiment of the present invention, potassium ferrocyanide and ferric sulfate are supplied to a cleaning solution used for cleaning dust ash and the like to produce Prussian blue (PB) containing radioactive cesium. A coprecipitation step may be included. In the coprecipitation step, PB containing radioactive cesium is obtained from the cleaning liquid containing radioactive cesium generated in S7 by a synthetic chemical coprecipitation reaction in the PB liquid. Specifically, the cleaning liquid containing radioactive cesium generated in S7 is sent to the raw water tank, and PB is generated by supplying potassium ferrocyanide and ferric sulfate to the raw water tank. And since PB adsorb | sucks radioactive cesium and aggregates and precipitates, PB containing radioactive cesium is isolate | separated from a washing | cleaning liquid by this. At this time, an inorganic or organic coagulating sediment may be added. Thereby, the separation efficiency of PB containing radioactive cesium can be further improved.

(S9: Concentration / adsorption process)
The method for removing radioactive cesium according to one embodiment of the present invention may include a concentration step of subjecting a solution containing radioactive cesium to electrodialysis to increase the concentration of radioactive cesium. The method for removing radioactive cesium according to one embodiment of the present invention may include an adsorption step in which a solution obtained by alkali decomposition of PB containing radioactive cesium is contacted with zeolite and the radioactive cesium in the solution is adsorbed on the zeolite. Good. In the concentration step, for example, the following processes (i) to (iii) may be repeated.

  (I) PB containing radioactive cesium is alkali-decomposed. For example, PB containing radioactive cesium is supplied to an alkali decomposition tank, alkali is added to the alkali decomposition tank, and PB containing radioactive cesium is decomposed into ferrocyanide ions and radioactive cesium ions.

  (Ii) The ferritocyanide ion and cesium ion are separated from the solution obtained in (i) above. For this separation, for example, an electrodialysis tank in which a cathode chamber and an anode chamber are partitioned by a cation exchange membrane can be used.

  (Iii) The solution containing cesium ions obtained in (ii) above is returned to the raw water tank of S8. The cesium ion is a cation and passes through the cation exchange membrane and collects in the cathode chamber of the electrodialysis tank, so that the solution on the cathode side of the electrodialysis tank is returned to the raw water tank.

  By repeating the steps (i) to (iii), a solution containing cesium ions at a high concentration can be obtained. When a solution concentrated to a predetermined concentration is obtained, the solution is subjected to an adsorption process. In the adsorption step, for example, the solution is supplied to a zeolite adsorption tank, and radioactive cesium is adsorbed on the zeolite in the adsorption tank. Thereby, radioactive cesium is removed from the said solution.

(S10: Firing and fixing step)
The method for removing radioactive cesium according to one embodiment of the present invention may include a firing fixing step of heating and fixing radioactive cesium by heating zeolite adsorbed with radioactive cesium. In the firing and fixing step, the zeolite adsorbed with radioactive cesium obtained in S9 is fired and fixed. The firing temperature is, for example, 1000 ° C. or higher. As a result, the radioactive cesium is difficult to elute, and the zeolite after firing and fixing can be finally disposed of as a stable final waste.

(S11: Treatment agent addition step)
In the method for removing radioactive cesium according to one embodiment of the present invention, a treatment agent that is an exhaust gas treatment agent that reacts with hydrogen chloride (hereinafter, simply referred to as a treatment agent) is supplied to exhaust gas generated by heating of the object to be treated. Then, a removal step of removing at least hydrogen chloride from the exhaust gas may be included. In the present embodiment, the removal step is referred to as a treatment agent addition step.

In the treatment agent addition step, the treatment agent is added to the exhaust gas after removing the dust fly ash in S6. The exhaust gas after removing the dust ash includes acid gases such as hydrogen chloride (HCl) and sulfur dioxide (SO ₂ ). It may also contain toxic substances such as dioxins. A processing agent is added in order to remove the above-mentioned acidic gas and toxic substance from waste gas, For example, slaked lime, baking soda, activated carbon, etc. may be included. The treating agent reacts with an acidic gas such as HCl contained in the exhaust gas to form a solid salt. Dioxins and the like are adsorbed on the activated carbon.

(S12: Second dust removal process)
The method for removing radioactive cesium according to one embodiment of the present invention may include a collection step of collecting desalted fly ash containing at least a treatment agent reacted with hydrogen chloride or the like. In the present embodiment, the removal step is referred to as a second dust removal step.

  In the second dust removal step, desalted fly ash containing a reaction product of the treatment agent produced by reacting with an acidic gas such as HCl and an unreacted treatment agent is removed from the exhaust gas. Desalinated fly ash collected by dust removal contains chlorides. For example, when slaked lime is contained in the treatment agent, slaked lime and HCl react to produce calcium chloride. Since calcium chloride functions as a separation accelerator, desalted fly ash containing calcium chloride can be used as a separation accelerator added in S2. Desalted fly ash may be used as at least a part of the separation accelerator. For example, the desalted fly ash may be used after adjusting the composition by adding other chlorides to the desalted fly ash. The purified exhaust gas after the dust ash is collected at S6 and the desalted fly ash is collected at S12 is discharged into the air.

(S13: Melting process)
The method for removing radioactive cesium according to one embodiment of the present invention may include a melting step. The incineration main ash generated in the incineration step (S3) can be disposed as it is if the radioactive cesium concentration is below the reference value. That is, if the concentration of radioactive cesium in the incinerated main ash is below the reference value, the removal of radioactive cesium is terminated. On the other hand, if the radioactive cesium concentration exceeds the reference value, the volume is reduced by the melting treatment in the melting step, and the radioactive cesium concentration is further reduced. The molten slag produced in the melting step and having a radioactive cesium concentration below the reference value can be recycled as a civil engineering resource.

  According to the method for removing radioactive cesium according to the present embodiment described above, the separation accelerator to be used and the incineration conditions are appropriately controlled, and most of the radioactive cesium contained in the object to be treated (for example, 90% or more). Can be volatilized. And thereby, content of radioactive cesium in incineration main ash can be suppressed low. For this reason, it is not necessary to wash the incinerated main ash with water, and various costs for treating the cleaning liquid and drying the incinerated main ash after washing are unnecessary.

  Here, non-patent literature “Experimental study on improvement of cesium separation efficiency in cesium volatile separation using melting technology”, Kamada, Nishimura, et al., 1st Environmental Radioactivity Decontamination Research Presentation, Poster Session, P-54, 2012.5.20 shows a result that the volatilization rate of cesium is about 82% when the actual incinerated ash having a Cl concentration of 0.6% is melted at 1450 ° C.

  Moreover, when the waste containing radioactive cesium is incinerated at about 900 degreeC, the result that 99% or more of radioactive cesium remains in incineration main ash has come out (refer the below-mentioned comparative example 3). Therefore, assuming that the radioactive cesium concentration of the waste is 10,000 Bq / kg and the ash content in the waste is 10 wt%, the radioactive cesium in the incinerated main ash is about 100,000 Bq / kg. .

  Even if such incinerated main ash is melted at 1450 ° C., if the Cl concentration in the incinerated main ash is about 0.6%, the volatility of radioactive cesium is 82% (in the equilibrium state, the cesium concentration in the gas is Is directly proportional to the concentration of cesium in the molten slag). Therefore, the radioactive cesium concentration of the molten slag is 18,000 Bq / kg. Such a molten slag has too high a radioactive cesium concentration, and cannot be used as a recycled material as it is.

  On the other hand, according to the method for removing radioactive cesium according to this embodiment, when a waste containing 10,000 Bq / kg of radioactive cesium is incinerated at about 900 ° C., a maximum of 93.1% of radioactive cesium is contained. Can be volatilized. In this case, if the ash content in the waste is 10 wt%, the radioactive cesium concentration in the incinerated main ash is about 6,900 Bq / kg. Therefore, by melting this incinerated main ash at 1450 ° C., the concentration of radioactive cesium in the molten slag can be reduced to 1,242 Bq / kg. Such a molten slag can be used as a recycled material. Thus, according to the method for removing radioactive cesium according to the present embodiment, a material having a radioactive cesium concentration of about 1/10 can be manufactured. In these trial calculations, the slag rate at the time of melting is not taken into consideration.

  Further, as described above, when the waste containing 10,000 Bq / kg of radioactive cesium is incinerated at about 900 ° C. by the method for removing radioactive cesium according to the present embodiment, the maximum is 93.1% of radioactive cesium. Can be volatilized. Assuming that the amount of fly ash at the time of incineration is 1.5% of the incineration amount (assuming ash content of 10 wt%, the amount of fly ash by scattering is assumed to be 15% of ash content), the radioactive cesium concentration in the fly ash is about 620,700 Bq / kg.

Here, since the separation accelerator containing the low melting point chloride is added to the object to be treated and incinerated, the hydrogen chloride gas in the exhaust gas becomes 1500 to 2000 ppm. This concentration is about 4 to 5 times that of ordinary municipal waste incineration exhaust gas. Since cesium chloride is soluble and the high concentration of hydrogen chloride gas is thought to contribute to increasing the elution rate of radioactive cesium, it is estimated that the elution rate of radioactive cesium in the fly ash is increased. Therefore, assuming that 95% of the radioactive cesium is removed by washing the incinerated fly ash with water, the concentration of radioactive cesium in the fly ash is about 31,000 Bq / kg. In addition, when the incinerated main ash and fly ash are mixed and melted at a ratio of 7: 3, the radioactive cesium in the object to be melted is 14,130 Bq / kg. And the radioactive cesium density | concentration in molten slag at the time of fuse | melting at 1450 degreeC will be 2,543Bq / kg, and if it is such molten slag, it can be utilized as a recycled material. When further reduction of radioactive cesium is required, the volatilization rate of radioactive cesium may be 99% or more by adding CaCl ₂ and activated carbon or the like to the object to be melted. As a result, the radioactive cesium concentration in the molten slag can be reduced to about 141 Bq / kg. This concentration is a value close to 100 Bq / kg determined by the clearance standard based on the Nuclear Energy Regulation Law.

[Configuration of treatment facility]
Next, the configuration of the processing facility 100 will be described with reference to FIG. The treatment facility 100 is a treatment facility that incinerates waste. The treatment facility 100 includes a crusher 2, a waste transport device 3, a waste pit 4, a crane 5, an incinerator 7, an incinerator main ash transport device 9, a gas cooling tower 10 (10A, 10B), a heat exchanger 11, a collector A dust device 12 (12A, 12B, 12C), a hopper 15, a melting furnace 16, and a cooling water tank 17 are provided. Further, the treatment facility 100 includes a washing tank 18, a raw water tank 19, an alkali decomposition tank 22, an anode chamber 26 and a cathode chamber 27, and an electrodialysis tank 24 having a cation exchange membrane 25 partitioning them, a zeolite adsorption tank 28. , A filtration device 30 and a treated water tank 31 are provided.

  The crusher 2 is a machine that crushes the waste 1 received as a processing object. The crushing step (S1) in FIG. 1 can be performed using the crusher 2. In addition, the waste transport device 3 is a device such as a conveyor that transports the waste 1 crushed by the crusher 2 to the waste pit 4. The waste pit 4 is a reservoir for temporarily storing the crushed waste 1 conveyed by the waste conveyance device 3. The crane 5 is a machine that stirs the waste 1 stored in the waste pit 4 and supplies it to the incinerator 7.

  The incinerator 7 is a facility for incinerating the waste 1. The incinerator 7 may be, for example, a stoker type incinerator, a rotary kiln type incinerator, or an incinerator using both of them. The incinerator 7 of FIG. 2 is a stoker type incinerator. The incineration step (S3) of FIG. 1 can be performed using the incinerator 7. In addition to the incinerator 7, the technology of the present embodiment can also be applied to a firing furnace, a melting furnace for waste or incinerated ash (ash generated by incineration such as incineration main ash and incineration fly ash). Technology.

  In addition, the addition process (S2) of FIG. 1 is performed before the incineration process which incinerates the waste 1 with the incinerator 7. FIG. For example, the separation accelerator 6 may be mixed and stirred with the waste 1 by the crane 5 in the waste pit 4. In addition, for example, the separation accelerator 6 is provided with a device such as a hopper or a chute in front of the device for supplying the waste 1 to the incinerator 7, and is supplied to the device using a conveying device such as a conveyor. Also good. In the example of FIG. 2, the separation accelerator is added by this method. Further, for example, the separation accelerator 6 may be directly supplied to a so-called drying stage which is an area where the temperature range of the incinerator 7 is relatively low, for example, an area close to the waste supply side of the incinerator 7.

  The separation accelerator 6 added to the waste 1 is at least one of a solid, a slurry (suspension), and an aqueous solution. Depending on how the separation promoter 6 is added to the waste 1, what shape and state of the separation promoter 6 should be determined. For example, as described above, when the waste 1 and the separation accelerator 6 are mixed and stirred in the waste pit 4, the separation accelerator 6 is preferably in the form of a solid. In this case, if the separation accelerator 6 that is a slurry or an aqueous solution is used, the separation accelerator 6 may flow down to the bottom surface of the waste pit 4 and may be difficult to be transported to the incinerator 7 by the crane 5. Because it is.

  Further, when the separation accelerator 6 is supplied to the front stage of the incinerator 7 by the transport device, the separation accelerator 6 is preferably a solid or slurry. In this case, if the separation accelerator 6 which is an aqueous solution is used, there is a possibility that the separation accelerator 6 flows down between the grate of the incinerator and the separation accelerator 6 and the waste 1 cannot be mixed. It is.

  When the separation accelerator 6 is directly supplied to the incinerator 7, it is necessary to pay attention to the blockage of equipment due to radiant heat from the incinerator 7 regardless of the shape of the separation accelerator 6. In addition, when the separation promoter 6 is sprayed and supplied to the incinerator 7 in the form of an aqueous solution, it is necessary to pay attention to an increase in the amount of auxiliary combustion used due to a decrease in the amount of heat in the incinerator 7.

  The incinerator main ash transport device 9 is a device that transports the incinerator main ash 8 that is collected by incineration of the waste 1 containing the separation accelerator 6 in the incinerator 7. The incinerator main ash transport device 9 may be, for example, a conveyor. The incinerator main ash transport device 9 transports the incinerator main ash 8 to the hopper 15. In addition, if the radioactive cesium density | concentration of the incinerator main ash 8 is below a reference value, it is not necessary to convey to the hopper 15.

  The gas cooling tower 10 is equipment for cooling the exhaust gas. The treatment facility 100 includes a gas cooling tower 10A that cools the exhaust gas generated by incineration of the waste 1 containing the separation accelerator 6 in the incinerator 7, and a gas cooling tower 10B that cools the exhaust gas from the melting furnace 16. ing. The cooling step (S4) in FIG. 1 can be performed using the gas cooling tower 10A. A part of the filtrate in the treated water tank 31 is sprayed as the cooling water B inside the gas cooling tower 10A. Although not shown, the filtrate in the treated water tank 31 may be used as cooling water in the gas cooling tower 10B.

  The heat exchanger 11 is a facility that recovers exhaust heat of exhaust gas. In addition, although illustration is abbreviate | omitted, the waste heat utilization equipment for performing the preheating of the combustion air utilized in an incinerator, electric power generation, or hot water supply using the waste heat collect | recovered by the heat exchanger 11 is a heat exchanger. 11 may be connected.

  Although not shown, a release agent supply device that supplies a release agent (filter aid) 13 to the exhaust gas discharged from the heat exchanger 11 is provided downstream of the heat exchanger 11. The release agent adding step (S5) in FIG. 1 is performed here.

  The dust collector 12 is a device that removes exhaust gas by collecting solids in the exhaust gas. The treatment facility 100 includes a first-stage dust collector 12A installed on the upstream side of the exhaust gas flow path, and a second-stage dust collector 12B installed in series with the dust collector 12A on the downstream side thereof. ing. Further, the processing facility 100 includes a dust collector 12C provided in the flow path of the exhaust gas from the melting furnace 16. For example, as shown in FIG. 2, the exhaust gas that has passed through the dust collector 12C may be treated with a treating agent together with the exhaust gas that has passed through the dust collector 12A. These dust collecting devices 12 may be bug filters, for example.

  The dust collector 12A collects solids such as dust and cesium salt (CsCl) contained in the exhaust gas. The first dust removal step (S6) in FIG. 1 can be performed using the dust collector 12A. Dust removal fly ash containing dust, cesium salt (CsCl) and the like collected by the dust collector 12A is sent to the cleaning tank 18.

  Although illustration is omitted, a chemical supply device that supplies a treatment agent to the exhaust gas that has passed through the dust collector 12A is provided between the dust collector 12A and the dust collector 12B. A processing agent is a chemical | medical agent containing slaked lime, baking soda, activated carbon, etc. The treatment agent may be supplied by spraying. The treatment agent addition step (S11) in FIG. 1 is performed by this medicine supply device. Acidic gases such as hydrogen chloride and dioxins contained in the exhaust gas that has passed through the dust collector 12A are removed by a chemical reaction or adsorption with a treatment agent supplied by the chemical supply device.

  The dust collector 12B collects desalted fly ash containing a reaction product that has reacted or adsorbed with the treating agent. The second dust removal step (S12) in FIG. 1 can be performed using the dust collector 12B. As described above, the desalted fly ash can be used as a separation accelerator added in S2. Therefore, the desalted fly ash collected by the dust collector 12 </ b> B may be added to the object to be treated as the separation accelerator 6. The exhaust gas that has passed through the dust collector 12B is discharged from the chimney into the air.

  The hopper 15 is a device for accommodating the incinerated main ash 8 conveyed by the incinerated main ash conveying device 9 and feeding it into the melting furnace 16 in a timely manner. The melting furnace 16 is a furnace for melting the incinerated main ash 8. The melting step (S13) in FIG. 1 can be performed using the melting furnace 16. The exhaust gas discharged from the melting furnace 16 is sent to the gas cooling tower 10. Incinerated main ash 8 melted in the melting furnace 16 is sent to the cooling water tank 17. The cooling water tank 17 is a water tank that contains cooling water for cooling the molten incineration main ash 8, and the molten incineration main ash 8 is cooled in the cooling water tank 17 and collected as molten slag. This molten slag can be used as a recycled material (for example, embankment or roadbed material).

  The cleaning tank 18 is a water tank for cleaning the dust removal fly ash with a cleaning liquid (for example, water). The fly ash cleaning step (S7) of FIG. 1 can be performed using the cleaning tank 18. In the cleaning tank 18, the dust fly ash collected by the dust collector 12 </ b> A can be washed, and the molten fly ash collected by the dust collector 12 provided in the exhaust gas flow path of the melting furnace 16. Can also be cleaned. The fly ash washed in the washing tank 18 may be removed after the removal of radioactive cesium if the radioactive cesium concentration is below the reference value, and may be subjected to a melting treatment if it exceeds the reference value.

  The raw water tank 19 is a reaction tank for a synthetic chemical coprecipitation reaction in a PB (Prussian blue) solution. The coprecipitation step (S8) in FIG. 1 can be performed using the raw water tank 19. A cleaning liquid containing radioactive cesium discharged from the cleaning tank 18 is stored in the raw water tank 19. PB containing radioactive cesium can be separated by supplying potassium ferrocyanide 20 and ferric sulfate 21 to the raw water tank 19 in which the cleaning liquid is accommodated.

  The alkaline decomposition tank 22 is a reaction tank for alkaline decomposition of PB containing radioactive cesium. The PB containing radioactive cesium obtained by the synthetic chemical coprecipitation reaction in the raw water tank 19 is accommodated in the alkali decomposition tank 22, and the alkali 23 is supplied to the PB containing the radioactive cesium and ferrocyanide ions. It can be decomposed into radioactive cesium ions.

  The electrodialysis tank 24 is a reaction tank for increasing the concentration of radioactive cesium by electrodialysis. A concentrated radioactive cesium solution can be obtained from the cathode chamber 27 by electrodialyzing the reaction solution subjected to alkali decomposition in the alkali decomposition vessel 22 in the electrodialysis vessel 24. The concentrated radioactive cesium solution may be returned to the raw water tank 19 again and subjected to a synthetic chemical coprecipitation reaction for further concentration. Concentration in the concentration / adsorption step (S9) of FIG. 1 can be performed using these water tanks (raw water tank 19, alkali decomposition tank 22, electrodialysis tank 24).

  The zeolite adsorption tank 28 is a reaction tank for adsorbing radioactive cesium on zeolite. The radioactive cesium solution concentrated as described above can be supplied to the zeolite adsorption tank 28 and the zeolite in the zeolite adsorption tank 28 can be adsorbed with the radioactive cesium. The adsorption in the concentration / adsorption process (S9) of FIG. 1 can be performed using the zeolite adsorption tank.

  The filtration device 30 is a device for filtering solid matter from the solution, and filters the solid matter from the solution after the radioactive cesium is adsorbed to the zeolite in the zeolite adsorption tank 28. The filtrate is sent to a treated water tank 31 that contains treated water. Since the filtrate in the treated water tank 31 is considered to contain radioactive cesium, it is preferably used effectively in the treatment facility 100. For example, as shown in FIG. 2, the inside of the incinerator 7 (for example, the secondary combustion chamber) may be sprayed and used as the cooling water A for the exhaust gas in the incinerator 7. Further, for example, as shown in FIG. 2, the cooling water B of the gas cooling tower 10 may be used.

[About chloride and melting point]
Next, the composition of the separation accelerator 6 will be described with reference to FIGS. As described above, a low melting point chloride having a melting point of 600 ° C. or less prepared using two or more types of chlorides is used for the separation accelerator 6 added to the object to be treated.

  FIG. 3 is a diagram showing the composition and melting point of the low melting point chloride. Each melting point shown in FIG. 3 is based on Masayo Yoshiba “High Temperature Technology and Material Innovation in Advanced Waste Treatment Plants”, Sanyo Technical Report Vol.6 (1999), No.1. Each of the low melting point chlorides in FIG. 3 is a mixture of two types of chlorides, each having a lower melting point than a single chloride, and therefore incineration under relatively low temperature conditions. Can also be used as an effective separation accelerator. However, low melting point chlorides containing toxic heavy metals such as lead are not suitable as the separation promoter 6 added to the object to be treated.

FIG. 4 is a phase equilibrium diagram of NaCl and CaCl ₂ . As shown in FIG. 4, the melting point of NaCl alone is 801 ° C. The single melting point of CaCl ₂ is 772 ° C. The low melting point chloride composed of NaCl and CaCl ₂ has a minimum melting point (504 ° C.) when the molar ratio is NaCl: CaCl ₂ = 49: 50.

In order to obtain a low melting point chloride having a melting point of 600 ° C. or lower, it is desirable to mix NaCl and CaCl ₂ in a molar equivalent range of 36 to 59 NaCl−41 to 64CaCl ₂ . Thus, a low melting point chloride in which NaCl and CaCl ₂ are mixed within a molar equivalent range where the melting point is 600 ° C. or less can be used as the separation accelerator 6.

  In addition, what is necessary is just to be in the state by which the separation promoter of a predetermined composition and the process target object were mixed by the time of incineration. For example, a part of chlorides, which are constituent elements of a separation accelerator having a predetermined composition, and other chlorides are individually added to the object to be treated, mixed, and after mixing, the separation accelerator is predetermined. The composition may be as follows. Further, a low melting point chloride, which is a double salt obtained by mixing two or more types of chlorides and melting them by heating, can also be used as the separation accelerator 6.

Here, as described above, the desalted fly ash containing the reaction product reacted or adsorbed with the treating agent can be used as the separation accelerator 6. Moreover, as this processing agent, slaked lime or baking soda can be used. Slaked lime reacts with hydrogen chloride in the exhaust gas to produce CaCl ₂ , and sodium bicarbonate reacts with hydrogen chloride in the exhaust gas to produce NaCl. For this reason, when using the processing agent containing slaked lime or baking soda, or both, it is preferable that the separation accelerator 6 contains NaCl, CaCl ₂ , or both. As a result, when desalted fly ash is used as the separation accelerator 6, the composition change between the separation accelerator 6 added first and the separation accelerator 6 using desalted fly ash is suppressed and stable. It is possible to maintain the removal rate of the radioactive cesium. In addition, desalted fly ash may be used as it is as a separation accelerator, or may be used as a separation accelerator after adjusting the components. Among low melting point chlorides containing NaCl and CaCl ₂ , it is more preferable to use 49NaCl.50CaCl ₂ or the like having a particularly low melting point.

[Modification]
In the said embodiment, although the example which volatilizes the radioactive cesium by combusting the process target object which is a combustible material, it heats without burning a process target object (typically the incombustible material containing radioactive cesium). A configuration for volatilizing radioactive cesium is also included in the scope of the present invention.

  Moreover, the composition and addition amount of the separation accelerator and the incineration conditions described above are examples. Depending on the configuration of the treatment facility 100 (particularly the incinerator 7), a large amount of radioactive cesium is volatilized from the object to be treated, and as long as the radioactive cesium remaining in the incineration main ash becomes almost water-insoluble radioactive cesium It is possible to adjust.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

[Additional Notes]
A method for removing radioactive cesium according to one embodiment of the present invention is a method for removing radioactive cesium from a processing object, and includes two or more types of chlorides, each having a melting point higher than a single chloride. The cesium separation accelerator containing the mixture or the double salt reduced in the above is added to the object to be treated, and the calcium content is 5% by weight or less in terms of calcium oxide concentration, and the separation accelerator and the above An addition step for obtaining a mixture of treatment objects, and a heating step for heating the mixture at 900 ° C. to 1000 ° C. to volatilize radioactive cesium from the treatment object. Of the remaining radioactive cesium, the amount of water-soluble radioactive cesium in the treated product is 1/5 or less of the total amount of radioactive cesium in the treated product. And amount of the separation accelerator in the degree, the heating time in the heating step is set.

  As a result of the studies by the inventors of the present application, when the amount of calcium contained in the mixture of the separation accelerator and the object to be treated is 5% by weight or less in terms of calcium oxide concentration, the comparison is 900 ° C. or more and 1000 ° C. or less. It has been found that radioactive cesium can be volatilized at a higher rate at a relatively low temperature as compared with the technology of Patent Document 1 mentioned above. Therefore, according to the above configuration, most of the radioactive cesium can be volatilized at a relatively low temperature of 900 ° C. or higher and 1000 ° C. or lower. Thereby, it becomes possible to process the processed material after the heating step without washing.

  Moreover, according to said structure, the quantity of the water-soluble radioactive cesium which remains in the processed material after a heating process can be restrained small. Thereby, it becomes easy to process the processed material after the heating step without washing.

  Further, among the radioactive cesium remaining in the treated product after the heating step, the amount of the separation accelerator added in the addition step and the heating in the heating step so that water-soluble radioactive cesium is 1500 Bq / kg or less. Time may be set.

  If water-soluble radioactive cesium is 1500 Bq / kg or less, the elution amount of water-soluble radioactive cesium under the condition of a solid-liquid ratio of 1:10 will be 150 Bq / L or less. Therefore, according to said structure, the elution amount of the radioactive cesium from the processed material after a heating process can be 150 Bq / L or less which is the elution reference value of the radioactive cesium from a radioactive waste. Thereby, it becomes possible to process the processed material after a heating process, without washing with water.

The separation accelerator is a mixture or a double salt containing NaCl and CaCl ₂ and having a melting point of 600 ° C. or lower, and is included in the mixture of the separation accelerator and the object to be treated heated in the heating step. The amount of chlorine produced is 1 to 2% by weight, and the heating time of the heating step may be 2 hours or more.

  According to said structure, most radioactive cesium in a process target object can be volatilized by heating, and the quantity of the water-soluble radioactive cesium in the processed material after a heating process can be suppressed very small.

  Furthermore, according to said structure, the amount of calcium and chlorine in a separation promoter are less than the amount of calcium and chlorine described in patent document 1 described in "background art." Therefore, radioactive cesium can be efficiently removed from the object to be processed while suppressing the amount of the separation accelerator used as compared with the technique of Patent Document 1. In addition, by suppressing the amount of the separation accelerator used, the amount of the heat-treated product (after the reaction or including the unreacted separation accelerator) generated after the heating step can be reduced.

  In the method for removing radioactive cesium, if the radioactive cesium concentration of the processed product after the heating step is equal to or lower than a predetermined reference value, the removal of the radioactive cesium from the processed product after the heating step is terminated, and the heating is performed. If the radioactive cesium concentration of the processed product after the process exceeds the predetermined reference value, the processed product after the heating process may be melted without washing. Here, the “predetermined reference value” may be, for example, 8,000 (Bq / kg), which is a reference value based on the above-mentioned special measures against radioactive material contamination countermeasures. The same applies to the “predetermined reference value” below.

  According to said structure, even if the radioactive cesium density | concentration of the processed material after a heating process is below a predetermined reference value, or exceeds the reference value, a process target object is not wash | cleaned. Therefore, costs such as equipment, energy, and time for cleaning are unnecessary.

  The method for removing radioactive cesium further includes a washing step of washing the fly ash containing radioactive cesium volatilized from the object to be treated in the heating step with a washing liquid to remove the radioactive cesium from the fly ash. If the radioactive cesium concentration of the fly ash is less than or equal to a predetermined reference value, the removal of the radioactive cesium from the fly ash is terminated, and the radioactive cesium concentration of the fly ash after washing exceeds the predetermined reference value. For example, the fly ash may be melted.

  According to said structure, even if the radioactive cesium density | concentration of the processed material after a heating process is below a predetermined reference value or exceeds the reference value, fly ash is not washed again. Therefore, the cost of equipment, energy, time and the like for cleaning can be minimized. The fly ash may contain molten fly ash generated by the melting process.

  Further, the method for removing radioactive cesium includes a cleaning step of cleaning the fly ash containing radioactive cesium volatilized from the object to be treated in the heating step with a cleaning liquid and removing the radioactive cesium from the fly ash, and the cleaning step. Supplying potassium ferrocyanide and ferric sulfate to the cleaning solution used to produce Prussian blue containing radioactive cesium and contacting the zeolite with the alkali-decomposed solution of Prussian blue containing radioactive cesium. An adsorption step of adsorbing radioactive cesium in the solution onto the zeolite and a calcining and fixing step of heating and fixing the radioactive cesium by heating the zeolite adsorbing the radioactive cesium may be included.

  According to said structure, the fly ash containing the radioactive cesium volatilized from the process target object is wash | cleaned with a washing | cleaning liquid. Since radioactive cesium volatilizes as water-soluble cesium chloride, most of the radioactive cesium contained in the fly ash can be taken into the cleaning liquid by this cleaning. Moreover, according to said structure, after separating radioactive cesium from a washing | cleaning liquid with Prussian blue and obtaining the solution of radioactive cesium again by alkali decomposition, the radioactive cesium in this solution is made to adsorb | suck to a zeolite. Thereby, high concentration radioactive cesium can be efficiently adsorbed on zeolite. And according to said structure, the zeolite which adsorb | sucked radioactive cesium is baked. Thereby, it can be set as the state which is hard to elute radioactive cesium and is easy to convey.

  The method for removing radioactive cesium further includes a concentration step in which the solution is subjected to electrodialysis to increase the concentration of radioactive cesium. In the adsorption step, the concentration of radioactive cesium is increased in the concentration step. Cesium may be adsorbed on the zeolite.

  According to said structure, since radioactive cesium is made to adsorb | suck to a zeolite from the solution with which the density | concentration of radioactive cesium increased, the adsorption | suction of radioactive cesium by a zeolite can be performed efficiently.

  In the method for removing radioactive cesium, the solution after the radioactive cesium is adsorbed on the zeolite in the adsorption step may be filtered and used as cooling water for cooling the exhaust gas generated in the heating step. Good.

  According to said structure, the removal process of radioactive cesium can be advanced using the solution after radioactive cesium was adsorb | sucked to a zeolite effectively. Moreover, since it is filtering, it can prevent that the microparticles | fine-particles contained in a solution clog a spray apparatus, piping, etc.

  Further, the method for removing radioactive cesium occurs in the removal step of supplying at least hydrogen chloride from the exhaust gas by supplying a treatment agent that reacts with hydrogen chloride to the exhaust gas generated in the heating step, and the removal step. And collecting the desalted fly ash containing at least the treating agent reacted with hydrogen chloride, and in the heating step, the separation accelerator prepared using the desalted fly ash The processing object to which is added may be heated.

  According to said structure, since the desalination fly ash produced when removing at least hydrogen chloride from this exhaust gas is utilized as a separation promoter, the usage-amount of a separation promoter can be suppressed. The desalted fly ash is preferably composed of a combination of two or more types of chlorides and contains a mixture or a double salt each having a melting point lower than that of a single chloride. In other words, the treatment agent added in the removal step reacts with the exhaust gas and is a combination of two or more chlorides, each of which produces a mixture or double salt having a melting point lower than that of a single chloride. Preferably there is. Thereby, radioactive cesium can be separated from the object to be processed at a relatively low heating temperature.

  Moreover, the treatment facility according to one embodiment of the present invention is a treatment facility that removes radioactive cesium from a treatment object, and includes a combination of two or more types of chlorides, each having a lower melting point than a single chloride. The cesium separation accelerator containing the prepared mixture or double salt is added to the object to be treated, and the amount of calcium contained is 5% by weight or less in terms of calcium oxide concentration and the object to be treated. An addition device for obtaining a mixture of products, and a heating furnace for heating the mixture at 900 ° C. or more and 1000 ° C. or less to volatilize radioactive cesium from the processing object, and a processed product after heating in the heating furnace Of the radioactive cesium remaining in the treated product, the addition device is attached so that the amount of water-soluble radioactive cesium in the treated product is 1/5 or less of the total amount of radioactive cesium in the treated product. And amount of the separating agent for promoting the heating time of the heating furnace is set. According to this treatment facility, the same effects as those of the method for removing radioactive cesium can be obtained.

  An embodiment of the present invention will be described with reference to FIGS. In addition, the Example described is an example and this invention is not limited to the structure of a present Example.

[Object to be treated]
The composition of the waste that is the object to be treated in this example is shown in FIG. FIG. 5 is a diagram showing the composition of waste that is the object to be treated in the examples and comparative examples of the present invention. This object to be treated is combustible waste having a combustible content of 45.5 (wt%), and contains 2800 Bq / kg of radioactive cesium. The chlorine content is as small as 0.04 (wt%). Calcium is contained in 3800 (mg / kg).

〔Test conditions〕
About Comparative Examples 1-17 and Examples 1-5, the said processing target object is incinerated in a tubular furnace under predetermined conditions, and the incinerated main ash after incineration is shaken at a solid-liquid ratio of 1:10 for 6 hours. Washed with water. The air ratio during incineration was 1.5. Moreover, the amount of CaO and the amount of Cl (both units are wt%) in the processing object after adding the separation accelerator were calculated. However, since Comparative Examples 1 to 3 are incinerated without adding a separation accelerator, the amount of CaO and the amount of Cl of the processing object itself are calculated.

  From the following formula, the amount of volatile radioactive cesium (volatile Cs), the amount of water-soluble radioactive cesium (insoluble Cs) in the incinerated main ash, and the amount of water-insoluble radioactive cesium (residual Cs) in the incinerated main ash (any FIG. 6 shows the percentage (%) with respect to the amount of (total cesium in the object to be treated) (unit: Bq). Moreover, the removal rate (Cs removal rate) of radioactive cesium was calculated | required from the water-insoluble radioactive cesium (residual cesium) amount in incineration main ash (unit:%).

  The radioactive cesium concentration in the object to be treated and the incineration main ash was measured using a germanium semiconductor detector, and the amount of cesium was calculated by the following equation.

{Cs amount (Bq)} = {Cs concentration (Bq / kg)} × {Sample amount (kg)}
In addition, the dissolved cesium concentration was prepared according to the method specified in “Japanese Industrial Standard K005-8-1” described in “Part 5: Radioactivity Concentration Measurement Guidelines” and “Chapter 8 Elution Volume” issued by the Ministry of the Environment. Similarly, measurement was performed using a germanium semiconductor detector.

(Volatile Cs) = (total cesium in the object to be treated) − (total cesium in the incineration main ash)
(Water-soluble Cs) = {elution cesium concentration (Bq / L)} × 10 (L / kg) × {incinerated main ash weight (kg)}
(Residual Cs) = (Total cesium in incineration main ash)-(Water-soluble cesium)
(Cs removal rate) = 100% − (residual cesium) / (total cesium in the object to be treated) × 100
[Test results: Comparative Examples 1 to 3]
In Comparative Examples 1 to 3, the treatment object was incinerated without adding a separation accelerator. At any incineration temperatures of 700 ° C., 800 ° C., and 900 ° C., there was no volatilization of radioactive cesium, and only a slight amount of water-soluble cesium was produced, and almost all of the radioactive cesium remained in the incineration main ash.

[Test results: Comparative Examples 4 to 6]
In Comparative Examples 4 to 6, 3.0 (wt%) of CaCl ₂ was added to the treatment object as a separation accelerator and incinerated at 700 ° C., 800 ° C., or 900 ° C. for 2 hours.

  In Comparative Example 4 where the incineration temperature is 700 ° C., the amount of volatile cesium is zero. However, as the incineration temperature increases, the amount of volatile cesium increases, and in Comparative Example 6 where the incineration temperature is 900 ° C., 87.3 (%) is obtained. Volatile cesium. Residual cesium decreased as the incineration temperature increased, and the minimum value was 10.2 (%) in Comparative Example 6 at an incineration temperature of 900 ° C. In Comparative Example 6, if 2.5 (%) of water-soluble cesium is removed by washing, 89.8% of radioactive cesium is removed as a whole. In addition, the most water-soluble cesium was 65.8 (%) in Comparative Example 4 having an incineration temperature of 700 ° C., and the amount of water-soluble cesium decreased as the incineration temperature increased.

[Test results: Comparative Examples 7 to 10, Example 1]
In Comparative Example 7-9, the 49NaCl · 50CaCl ₂ as a separation accelerator to the processing object 3.0 (wt%) was added, 700 ° C., incinerated 2 hours at 800 ° C., or 900 ° C.. Further, Comparative Example 10 differs from Comparative Example 8 only in incineration time. The incineration time of Comparative Example 10 is 0.5 hours shorter than Comparative Example 8.

  The results of Comparative Examples 7 to 9 are generally similar to those of Comparative Examples 4 to 6, and the amount of volatile cesium increases as the incineration temperature increases. In Example 1, which is an incineration temperature of 900 ° C., 81.6 ( %) Was volatile cesium. Further, the residual cesium decreased as the incineration temperature increased, and reached a minimum value of 6.6 (%) in Comparative Example 9 having an incineration temperature of 900 ° C. In Comparative Example 9, if 11.8 (%) of water-soluble cesium is removed by washing with water, 93.4% of radioactive cesium is removed as a whole. As for the results of Comparative Examples 7 to 9, the proportion of volatile cesium is small compared to Comparative Examples 4 to 6, but the proportion of water-soluble cesium is large. For this reason, it is possible to raise the removal rate of the radioactive cesium as a whole by washing | cleaning of incineration main ash on the conditions of Comparative Examples 7-9.

  In Comparative Example 10, the amount of volatile cesium was suppressed and the proportion of water-soluble cesium was increased by shortening the incineration time as compared with Comparative Example 8, compared with Comparative Example 8. However, since the amount of residual cesium is 27.3 (%), even if the incinerated main ash is washed, the overall removal rate of radioactive cesium is lower than that of Comparative Example 8.

[Test results: Comparative Examples 11 to 13]
In Comparative Example 11~13, 49NaCl · 50CaCl ₂ to 1.5,4.5 as a separation promoter to the processed object or 6.0 (wt%) was added, and incinerated 2 hours at 800 ° C..

  As the amount of the separation accelerator added increased, the proportion of volatile cesium decreased and the proportion of water-soluble cesium increased. The residual cesium decreased as the amount of the separation accelerator added increased, and the minimum value was 10.0 (wt%) in Comparative Example 13 in which 6.0 (wt%) was added. In these examples, the water-soluble cesium increased when the Cl concentration in the object to be treated after the addition of the separation accelerator was about 3.0 (wt%). Therefore, when a separation accelerator (more specifically, a Cl source) is added so that the Cl concentration is about 3.0 (wt%), incineration main ash must be washed to increase the removal rate of radioactive cesium. It is essential.

[Test results: Example 1, Comparative Example 14]
In Example 1 and Comparative Example 14, as in Comparative Example 9, 49NaCl · 50CaCl ₂ was added as a separation accelerator to the treatment object and incinerated at 900 ° C. for 2 hours. Example 1 and Comparative Example 14 differ from Comparative Example 9 in the amount of separation accelerator added. Specifically, the addition amount of Example 1 was 1.5 (wt%), which is smaller than that of Comparative Example 9, and the addition amount of Comparative Example 14 was 4.5 (wt%), which was larger than that of Comparative Example 9.

  In Comparative Example 14 in which the addition amount of the separation accelerator was increased from that in Comparative Example 9, the amount of volatile cesium and the amount of residual cesium increased compared to Comparative Example 9. On the other hand, in Example 1 in which the addition amount of the separation accelerator was reduced from that in Comparative Example 9 and both the CaO and Cl concentrations after the addition of the separation accelerator were about 1.0 (wt%), the radioactive cesium 90 % Could be volatilized. In Example 1, the radioactive cesium remaining in the incinerated main ash had a water solubility of 0.7 (%) and a water insolubility of 10.7 (%).

  Further, Example 1 and Comparative Example 11 differed only in incineration temperature, but a large difference occurred in the amount of residual cesium. That is, even when both the CaO and Cl concentrations after the addition of the separation accelerator are set to about 1.0 (wt%), incineration at 800 ° C. (Comparative Example 11) causes volatile cesium to be 37.0 ( %). Even when 17.0 (%) of water-soluble cesium was removed by washing with water, the removal rate of radioactive cesium was only 54.0 (%). From this, in order to increase the removal rate of radioactive cesium, it is only necessary to incinerate at 900 ° C. or higher after setting both the CaO and Cl concentrations after the addition of the separation accelerator to about 1.0 (wt%). I understand.

Here, a processing object having a radioactive cesium concentration of 10,000 Bq / kg and an ash content of 10 (wt%) is incinerated under the conditions of Example 1, that is, 1.5 wt% of 49 NaCl · 50 CaCl ₂ is added to 900 degrees. And incinerated for 2 hours.

  In this case, since the water-soluble cesium in the incinerated main ash is 0.7 (%) according to the result of Example 1, the concentration of the water-soluble cesium in the incinerated main ash of the treatment target is 10,000 Bq / It is estimated that kg × (100/10) × (0.7 / 100) = 700 Bq / kg. Moreover, about this incineration main ash, the elution amount of radioactive cesium at the time of performing a dissolution test by solid-liquid ratio 1:10 is calculated with 70 Bq / L. Further, the concentration of radioactive cesium in the incinerated main ash (total of water-soluble cesium and water-insoluble cesium) is 10,000 Bq / kg × (100/10) × (0.7 + 10.7) / 100 = 11,400 Bq / Estimated kg.

  Since the above radioactive cesium concentration exceeds the standard value (8,000 Bq / kg), this incinerated main ash cannot be disposed of as it is. However, this incinerated main ash can be subjected to a melting process without a water washing process to further reduce the volume and reduce the cesium concentration. And by such a melting process, it becomes possible to produce | generate the molten slag whose radioactive cesium density | concentration became less than a reference value, and to recycle this.

  On the other hand, if the above processing object is incinerated under the conditions of Comparative Example 3, that is, incinerated at 900 degrees for 2 hours without adding a separation accelerator, the concentration of radioactive cesium in the incinerated main ash is 10 times that before incineration. Is estimated to be 100,000 Bq / kg. Compared to this concentration, 11,400 Bq / kg, which is a trial calculation result corresponding to Example 1, is about 1/10 times. For this reason, it is considered that the radioactive cesium concentration in the molten slag is also about 1/10 times.

[Test results: Examples 2 to 4 and Comparative Examples 15 and 16]
Examples 2 and 3, Comparative Examples 15 and 16, the ones that the 49NaCl · 50CaCl ₂ and CaCO ₃ as a separate accelerator were mixed in a weight ratio 20:10 3.0 (wt%) the processing target prepared by adding 2 Incinerated for hours. The CaO and Cl concentrations after addition of the separation accelerator are about 1.6 (wt%) and about 1.3 (wt%), respectively. The incineration temperatures are different in Examples 2 and 3 and Comparative Examples 15 and 16, which are 700 ° C. in Comparative Example 15, 800 ° C. in Comparative Example 16, 900 ° C. in Example 2, and 1000 ° C. in Example 3. Moreover, Example 4 changes the incineration time of Example 2 into 4 hours.

  Although the volatile cesium was zero in the comparative example 15 which is an incineration temperature of 700 ° C., the amount of the volatile cesium increases as the incineration temperature becomes higher. In Example 3, which is an incineration temperature of 1000 ° C., 96.3 (%) was volatile cesium. Further, the residual cesium decreases as the incineration temperature becomes higher, 5.6 (%) in Example 2 which is an incineration temperature of 900 ° C., and 3.6 (%) in Example 3 which is an incineration temperature of 1000 ° C. became. Furthermore, in Examples 2 and 3, the amount of water-soluble cesium could be reduced to 1.3 (%) and 0.1 (%), respectively. Further, in Example 4 in which the combustion time was longer than that in Example 2, the amount of residual cesium decreased slightly and the amount of water-soluble cesium decreased compared to Example 2.

In Comparative Examples 15 and 16, even when water-soluble cesium was removed by washing with water, the removal rates of radioactive cesium were only 66.6 (%) and 75.5 (%), respectively. Therefore, when used as a 49NaCl · 50CaCl ₂ and CaCO ₃ as a separate accelerator were mixed in a weight ratio 20:10, in order to increase the removal rate of radioactive cesium, it can be seen that it is sufficient incinerated at 900 ° C. or higher .

  About Example 2, when the same calculation as Example 1 was performed, the water-soluble cesium density | concentration in the incineration main ash of a process target object will be 10,000 Bq / kg x (100/10) x (1.3 / 100) = 1,300 Bq / kg. Moreover, about this incineration main ash, the elution amount of radioactive cesium at the time of performing a dissolution test by the solid-liquid ratio 1:10 is estimated with 130 Bq / L. Further, the concentration of radioactive cesium in the incineration main ash (total of water-soluble cesium and water-insoluble cesium) is 10,000 Bq / kg × (100/10) × (1.3 + 5.6) / 100 = 6,900 Bq / Estimated kg.

  Since the radioactive cesium concentration is less than the standard value, the incinerated main ash can be disposed of. Moreover, said radioactive cesium density | concentration is about 1 / 14.4 of the trial calculation result of the comparative example 3. FIG. When the incineration main ash is melted, it is considered that molten slag having a lower radioactive cesium concentration than Example 1 can be generated.

[Test results: Example 5, Comparative Example 17]
Example 5, Comparative Example 17, was burned for two hours the treated object was added that the 49NaCl · 50CaCl ₂ and CaCO ₃ as a separate accelerator were mixed in a weight ratio 20:20 at 900 ° C.. The addition amount of the chemical | medical agent (separation promoter) of Example 5 is 4.0 (wt%), and the comparative example 17 is 6.0 (wt%).

  Although the Cl concentration was the same as Example 2, the amount of water-soluble cesium in Example 5 with a higher CaO amount than in Example 2 was lower than that in Example 2. On the other hand, in Comparative Example 17 in which the Cl concentration is higher than that in Example 2, specifically, the Cl concentration is close to 2 (wt%), the amount of water-soluble cesium is larger than that in Example 2, and 3.2. (%).

  For this reason, when processing a process target object on the conditions of the comparative example 17, depending on the radioactive cesium density | concentration of a process target object, washing | cleaning of incineration main ash may be needed. For example, when a waste (ash content: 10 wt%) having a radioactive cesium concentration of 10,000 Bq / kg is a treatment target, the concentration of water-soluble cesium in the incinerated main ash is 3,200 Bq / kg. The cesium elution amount is estimated to be 320 Bq / L exceeding the reference value.

[Examples in which the amount of water-soluble cesium in the incinerated main ash is small]
In Examples 1 to 5, the amount of water-soluble radioactive cesium in the incinerated main ash was very small, being 1/5 or less of the total amount of radioactive cesium in the incinerated main ash. From the conditions of these examples, the Cl concentration in the mixture obtained by mixing the processing object and the separation accelerator is 0.9 to 1.5 (wt%), and the CaO amount is 1 to 2.5 (wt%). It can be seen that it is preferable to add a separation accelerator to the mixture and heat at 900 to 1000 ° C. for 2 to 4 hours. By treating the object to be treated under these conditions, it becomes possible to treat the incinerated main ash without washing.

6 Separation accelerator 7 Incinerator (heating furnace)
8 Incinerated main ash (processed product after heating process)
100 treatment facility

Claims (8)

A method for removing radioactive cesium that removes radioactive cesium from a processing object,
A cesium separation accelerator comprising a combination of two or more types of chlorides, each containing a mixture or double salt having a melting point lower than that of a single chloride, is added to the treatment object, and the amount of calcium contained is increased. An addition step of obtaining a mixture of the separation accelerator and the treatment object, which is 1 to 2.5 (wt%) in terms of calcium oxide concentration,
Heating the mixture at 900 ° C. or higher and 1000 ° C. or lower to volatilize radioactive cesium from the processing target, and
Of the radioactive cesium remaining in the processed product after the heating step, the amount of water-soluble radioactive cesium in the processing object is 1/5 or less of the total amount of radioactive cesium in the processing object. The addition amount of the separation accelerator in the addition step is set so that the Cl concentration in the mixture obtained by mixing the treatment object and the separation accelerator is 0.9 to 1.5 (wt%), The heating time in the heating process is set to 2 to 4 hours,
If the radioactive cesium concentration of the processed product after the heating step is below a predetermined reference value, the removal of the radioactive cesium from the processed product after the heating step is terminated,
If the radioactive cesium concentration of the processed product after the heating step exceeds the predetermined reference value, the processed product after the heating step is melted without being washed with water, and the method for removing radioactive cesium is characterized in that .   Of the radioactive cesium remaining in the treated product after the heating step, the amount of the separation accelerator added in the addition step and the heating time in the heating step so that water-soluble radioactive cesium is 1500 Bq / kg or less, The method for removing radioactive cesium according to claim 1, wherein The method for removing radioactive cesium according to claim 1 or 2, wherein the separation accelerator is a mixture or a double salt containing NaCl and CaCl ₂ and having a melting point of 600 ° C or lower. The method further includes a washing step of removing the radioactive cesium from the fly ash by washing the fly ash containing the radioactive cesium volatilized from the object to be treated in the heating step,
If the concentration of radioactive cesium in the fly ash after washing is below a predetermined reference value, the removal of radioactive cesium from the fly ash is terminated,
If radioactive cesium concentration of the fly ash after cleaning exceeds the predetermined reference value, and melt processing the fly ash,
The processed product after the heating step is incinerated main ash,
The method for removing radioactive cesium according to any one of claims 1 to 3, wherein the fly ash is a solid in the exhaust gas generated in the heating step . A cleaning step of removing the radioactive cesium from the fly ash by washing the fly ash containing the radioactive cesium volatilized from the object to be treated in the heating step;
A coprecipitation step of supplying potassium ferrocyanide and ferric sulfate to the cleaning solution used in the cleaning step to generate Prussian blue containing radioactive cesium;
An adsorption step in which a solution obtained by alkali decomposition of the Prussian blue containing radioactive cesium and a zeolite are contacted, and the radioactive cesium in the solution is adsorbed on the zeolite;
And calcining the fixed firing fixing radioactive cesium by heating the zeolite to adsorb radioactive cesium, only including,
The processed product after the heating step is incinerated main ash,
The method for removing radioactive cesium according to any one of claims 1 to 4, wherein the fly ash is a solid in the exhaust gas generated in the heating step . Further comprising a concentration step of subjecting the solution to electrodialysis to increase the concentration of radioactive cesium,
6. The method for removing radioactive cesium according to claim 5, wherein in the adsorption step, radioactive cesium is adsorbed on zeolite from the solution in which the concentration of radioactive cesium is increased in the concentration step.   7. The method according to claim 5, wherein the solution after the radioactive cesium is adsorbed on the zeolite in the adsorption step is filtered and used as cooling water for cooling the exhaust gas generated in the heating step. To remove radioactive cesium A processing facility for removing radioactive cesium from a processing object,
A cesium separation accelerator comprising a combination of two or more types of chlorides, each containing a mixture or double salt having a melting point lower than that of a single chloride, is added to the treatment object, and the amount of calcium contained is increased. An addition device for obtaining a mixture of the separation accelerator and the treatment object, which is 1 to 2.5 (wt%) in terms of calcium oxide concentration;
A heating furnace in which the mixture is heated at 900 ° C. or higher and 1000 ° C. or lower to volatilize radioactive cesium from the processing object,
Of the radioactive cesium remaining in the treated product after heating in the heating furnace, the amount of water-soluble radioactive cesium in the treated product is 1/5 or less of the total amount of radioactive cesium in the treated product. In addition, the amount of the separation accelerator added by the addition device is set so that the Cl concentration in the mixture obtained by mixing the object to be treated and the separation accelerator is 0.9 to 1.5 (wt%). The heating time in the heating step in the heating furnace is set to 2 to 4 hours,
If the radioactive cesium concentration of the processed product after the heating step is below a predetermined reference value, the removal of the radioactive cesium from the processed product after the heating step is terminated,
If the radioactive cesium density | concentration of the processed material after the said heating process exceeds the said predetermined reference value, the processed material after the said heating process will be melt-processed without water-washing.

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