JP2013120147A - Method for treating radioactive cesium contaminated materials - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology for reducing a cesium concentration level of radioactive cesium flying in the exhaust gas system of an incinerator for incinerating large quantities of radioactive cesium contaminated materials occurring due to the Fukushima Daiichi nuclear disaster that are trees, clothing of operators, and other combustibles occurring in large quantities inside/outside the premises of the nuclear power plants in order to reduce them to ashes.SOLUTION: Combustibles with radioactive cesium of CsCOtype and CsO type attached thereto and a chlorine compound are charged into the incinerator and subsequently heated up to a decomposition temperature range of the radioactive cesium of CsCOtype and CsO type while mixed; the radioactive cesium occurring in the decomposition temperature range is made to be cesium chloride; the combustibles are incinerated at an incineration temperature of the melting point or more and the boiling point or below of the cesium chloride; and the cesium chloride is absorbed into incineration bottom ash generated by the incineration.

Description

  The present invention relates to a method for treating radioactive cesium contaminants generated in large quantities on the premises of a nuclear power plant, particularly due to the accident at the Fukushima Daiichi nuclear power plant.

  Due to the accident at the Fukushima Daiichi Nuclear Power Station that occurred on March 11, 2011, a large amount of disaster waste contaminated with radioactive cesium (hereinafter referred to as radioactive cesium pollutants) was generated inside and outside the site of the nuclear power station.

  As for the disaster waste generated outside the site of the nuclear power plant at present, as a guideline of the Ministry of the Environment regarding the disposal of these radioactive cesium pollutants, the general waste final disposal site for those with a radioactivity concentration of 8000 Bq / kg or less For landfills with a radioactive concentration of over 8000 Bq / kg, the behavior of radioactive cesium will be properly grasped and temporarily managed at the final disposal site until the safety of disposal is confirmed by the government. Storage is shown (Non-patent Document 1).

  On the other hand, although no national guidelines are provided for the disposal of radioactive waste generated by disasters on the site of a nuclear power plant, combustibles are incinerated from the viewpoint of volume reduction of waste. It is desirable to store temporarily after incineration ash is processed.

  This time, a large amount of new combustibles such as trees and clothing worn by workers engaged in accident handling work are generated on the site of the nuclear power plant. Expansion is an urgent need.

  By the way, regarding the treatment technology of combustible miscellaneous solid waste generated in a normal nuclear power plant, the applicants of the present application disclose various technologies. For example, Non-Patent Document 1 shows that in incineration at a nuclear facility, 69% of radioactive cesium contained in waste remains in the incineration main ash. It is expected that the radioactive cesium contamination that is treated this time will show the same behavior. In this case, 31% of the radioactive cesium is scattered in the exhaust gas system as fly ash and collected by a ceramic filter, a HEPA filter, or the like.

  Regarding the design of the exhaust gas system, the level of so-called “welding management” is also strictly defined according to the cesium concentration level. For example, a large amount of radioactive cesium contamination, which is the disaster waste of this time, is incinerated, 31% of which Is assumed to be scattered in the exhaust gas system as fly ash, “welding management” is at a level that requires various rigorous inspections such as inspection by X-rays, resulting in high costs and difficult exhaust gas system maintenance management There is a problem to become.

vol. 30, no. 6 (1988) Decontamination performance in the exhaust gas treatment system of radioactive solid waste incineration facilities P.47-54

  The object of the present invention is to solve the above-mentioned problems, and among the radioactive cesium pollutants generated in large quantities due to the accident at the Fukushima Daiichi nuclear power plant, trees and workers generated in large quantities inside and outside the site of the nuclear power plant It is to provide a technique for reducing the cesium concentration level of radioactive cesium scattered in an exhaust gas system in an incinerator for reducing the volume of combustible materials such as clothing as incineration ash.

The method for treating radioactive cesium contaminants according to the present invention, which has been made to solve the above-mentioned problems, includes combustible substances and chlorine compounds, to which Cs ₂ CO ₃ type and Cs ₂ O type radioactive cesiums are attached, in an incinerator. After charging, the mixture is heated to the decomposition temperature range of the Cs ₂ CO ₃ type and Cs ₂ O type radioactive cesium while mixing, and the radioactive cesium generated in the decomposition temperature range is converted to cesium chloride and the combustible material is chlorinated. Incineration is carried out at an incineration temperature not lower than the melting point and lower than the boiling point of cesium, and the cesium chloride is taken into the incineration main ash generated by the incineration.

  Invention of Claim 2 is a rotary kiln provided with the sodium chloride aqueous solution spray nozzle which sprays the sodium chloride aqueous solution toward the inside of the incinerator in the processing method of the radioactive cesium contaminant of Claim 1 It is characterized by.

  According to a third aspect of the present invention, there is provided the method for treating radioactive cesium contaminants according to the second aspect, wherein the rotary kiln is rotatably supported by a horizontal rotary drum, an outer shell having a sealed structure covering the outer periphery thereof, and an outer shell A radioactive waste input part that reaches one end of the rotary drum and an exhaust gas outlet part connected to the other end of the rotary drum, each of the radioactive waste input part and the exhaust gas outlet part being external It is connected to the shell in an airtight manner, the exhaust gas outlet is provided with a burner for burning radioactive waste that blows flame into the rotating drum, and the incineration residue discharge port is provided at the bottom of the exhaust gas outlet. It is a feature.

  According to a fourth aspect of the present invention, in the method for treating radioactive cesium contaminants according to the third aspect, the rotary kiln is further connected to the incineration residue discharge port with a stalker portion whose outer periphery is covered with an outer shell having a sealed structure. It is characterized by

In the method for treating radioactive cesium contaminants according to the present invention, a combustible material to which Cs ₂ CO ₃ type and Cs ₂ O type radioactive cesium adheres and a chlorine compound are introduced into an incinerator and then mixed with the Cs ₂ Heating to the decomposition temperature range of CO ₃ type and Cs ₂ O type radioactive cesium, the radioactive cesium generated in the decomposition temperature range to cesium chloride, incineration of the combustible material above the melting point and below the boiling point of cesium chloride By incinerating at a temperature and incorporating the cesium chloride into the incinerated main ash generated by the incineration, it is possible to effectively suppress the phenomenon that radioactive cesium is scattered as fly ash in the exhaust gas system outside the incinerator.

  By effectively suppressing the phenomenon where radioactive cesium is scattered as fly ash in the exhaust gas system outside the incinerator, it is possible to lower the "welding management" of the exhaust gas system from the level where various strict inspections are required. Costs associated with “management” can be reduced. In addition, it is possible to simplify the equipment configuration of the exhaust gas system and avoid the danger of exposure accidents of workers during maintenance work.

It is a longitudinal cross-sectional view of the rotary kiln of a sealing structure.

  Preferred embodiments of the present invention are shown below.

The radioactive cesium generated by the earthquake is present in the metal Cs immediately after the accident, but becomes Cs ₂ O after contact with the atmosphere and finally becomes Cs ₂ CO _3, and then dissolves in the water due to rain or the like Cs ₂ It is assumed that CO ₃ has fallen on the ground and is attached to trees.

Cs ₂ CO ₃ has a chemical property that it melts at 610 ° C. and decomposes at the same time, and becomes Cs ₂ O (decomposed at 400 ° C.) or Cs (boiling point 678 ° C.) by decomposition. At a general incineration temperature of 800 ° C., the decomposition temperature is equal to or higher than the boiling point. Theoretically, cesium cannot remain in the incineration ash and is scattered in the fly ash.

  In contrast, the present invention treats radioactive cesium contaminants while supplying a sodium chloride aqueous solution into the incinerator, leaving the radioactive cesium as cesium chloride in the incineration main ash, and the radioactive cesium is put into the fly ash. It is to avoid scattering.

  Cesium chloride has a melting point of 645 ° C. and a boiling point of 1290 ° C., and is a liquid in an incineration temperature range of 700 to 900 ° C., is not easily volatilized, and is not a solid particle. be able to. The incineration temperature range is not less than the melting point of cesium chloride and not more than the boiling point, particularly preferably 700 to 900 ° C.

  The incinerator type is preferably a rotary kiln type. In particular, a sodium chloride spray nozzle 6 for spraying sodium chloride toward the inside of the rotary kiln having a closed structure (JP-A 2010-38534) filed by the applicant of the present application. The one with is best.

  Specifically, as shown in FIG. 1, it is composed of a radioactive waste input part 1, an exhaust gas outlet part 2, a rotating drum 3 and an outer shell 4. The rotating drum 3 is made of SUS or carbon steel. It has a structure in which a refractory material is lined on the inner surface, and is rotatably supported so that the center line is substantially horizontal between the radioactive waste input part 1 and the exhaust gas outlet part 2, and the outer shell 4 is made of carbon steel. The rotary drum 3 is configured to be rotatably mounted by the rotary support means 20.

  Of the openings 8 provided at both ends of the outer shell 4, the radioactive waste input portion 1 is flange-connected at one end, and the exhaust gas outlet portion 2 is flange-connected at the other end, so that the inside of the outer shell 4 has a sealed structure. Yes. The outer shell 4 includes a combustion air inlet 12 and a combustion air supply means 13. The inside of the outer shell 4 is kept at a negative pressure. The radioactive waste input unit 1 includes radioactive waste input dampers 9a and 9b that are double stacked on the input port, and a pusher 10 on the bottom. At the lower part of the exhaust gas outlet 2, a radioactive waste combustion burner 11 having a nozzle opened in the direction of the rotary drum 3 is provided, and an incineration residue discharge port 17 is provided at the bottom. Further, the exhaust gas outlet portion includes a temperature measurement hole 18 and a water spray nozzle 19 opened in the direction of the rotating drum. In addition, a closed stoker furnace 5 may be connected to the lower portion of the incineration residue discharge port 17. The stalker furnace 5 is preferably one in which the entire outer surface is sealed with a steel outer shell and a refractory is applied to the inner surface.

  According to the rotary kiln, the waste and the aqueous sodium chloride solution are supplied from the same direction, and the rotation function allows the waste to which cesium carbonate or the like adheres to be quickly mixed with sodium chloride, and cesium carbonate decomposes at 500 ° C. Can be mixed and brought into contact until the temperature range is reached. As a result, cesium chloride can be more reliably obtained. The combustible material in the waste thrown into the rotary kiln is incinerated at an incineration temperature not lower than the melting point and not higher than the boiling point of cesium chloride. Most of the cesium chloride produced in the previous stage of the rotary kiln is taken in by adhering to the incineration main ash produced in the middle stage or later of the rotary kiln.

  The radioactive cesium adhering to the incineration main ash in the form of sodium chloride is continuously discharged in the rotary kiln, so it does not reach a high temperature close to the boiling point of the radioactive cesium in the furnace, and the phenomenon of scattering to the exhaust gas system as fly ash It can be avoided reliably. In addition, by using a rotary kiln type incinerator, a sufficient residence time in the furnace can be ensured, so that a stable cesium residual rate can be obtained.

  In addition, the method of supplying sodium chloride as spray water of sodium chloride aqueous solution is optimal. According to the method, sodium chloride can be uniformly supplied to the waste. For example, protective equipment (Tyvek) frequently used in nuclear power plants is stored in a polyethylene bag. When this is put into a rotary kiln, the polyethylene bag will have its original shape when it is just supplied. Although it is kept, it shrinks with time, and the internal protective equipment is exposed and scattered in the furnace. Next, when the thermal contraction of the protective equipment starts and the decomposition temperature reaches about 500 ° C., gasification starts and combustion starts. In order to follow such a combustion process, it is necessary to spray sodium chloride continuously as an aqueous solution.

Simulated waste (wood, cloth, paper, polyethylene, rubber) was incinerated at 800 ° C. using a rotary kiln. The form of cesium was added as sprinkled to the simulated waste as Cs ₂ CO ₃ .

  In the rotary kiln, water may be sprayed to control the temperature in the furnace, but in this example, sodium chloride was added to this water and sprayed continuously into the furnace at a concentration of 1%. In this case, the chlorine supply amount is 0.67 wt% with respect to the simulated waste amount. Spraying sodium chloride aqueous solution in a rotary kiln type incinerator to waste, and the waste to be charged is stirred by the rotation of the furnace and mixed well with sodium chloride. Therefore, radioactive cesium is mixed with cesium chloride. Very convenient to convert to form. Sprayed sodium chloride is preferably supplied from the waste input side in terms of preferential reaction between radioactive cesium and chlorine. In vertical or horizontal fixed-bed incinerators used in conventional nuclear power plants, sodium chloride and waste cannot be mixed in this way. Therefore, for example, sodium chloride is supplied in normal waste properties. However, the effect like a rotary kiln cannot be obtained.

  Incinerated main ash was prepared under the above conditions. For comparison evaluation, an incinerated main ash treated without containing sodium chloride was also prepared.

  As a result of measuring the Cs concentration in the incinerated main ash, the residual ratio of cesium in the incinerated ash was 95% when sodium chloride was supplied and 60% when sodium chloride was not supplied. According to the method of the present invention, radioactive cesium As cesium chloride, it was confirmed that it was possible to effectively suppress the phenomenon of fly ash scattering into the exhaust gas system outside the incinerator as fly ash. Thereby, since the radioactivity density | concentration in exhaust gas flue can be reduced, the radioactivity density | concentration of a downstream exhaust gas processing apparatus can be reduced, and the advantage that simplification of a shield design or an easy maintenance will also arise.

  Although the above describes the combustible material in the nuclear power plant, it is obvious that it can be applied as a means for reducing the radioactive concentration of the exhaust gas system in the treatment of combustible material contaminated with radioactive cesium outside the nuclear power plant.

DESCRIPTION OF SYMBOLS 1 Radioactive waste input part 2 Exhaust gas outlet part 3 Rotating drum 4 Outer shell 6 Sodium chloride spray nozzle 8 Openings 9a, 9b Damper 10 for radioactive waste injection Pusher 11 Burner 12 for burning radioactive waste Combustion air inlet 13 Combustion air Supply means 17 Incineration residue outlet 18 Temperature measurement hole 19 Water spray nozzle 20 Rotating support means

Claims (4)

Combustion material to which Cs ₂ CO ₃ type and Cs ₂ O type radioactive cesium is attached and a chlorine compound are put into an incinerator and then decomposed while mixing with mixing Cs ₂ CO ₃ type and Cs ₂ O type radioactive cesium Heat until it reaches the temperature range,
The radioactive cesium generated in the decomposition temperature range is cesium chloride,
A method for treating radioactive cesium contaminants, comprising combusting combustible materials at an incineration temperature not lower than the melting point and lower than the boiling point of cesium chloride, and incorporating the cesium chloride into incineration main ash generated by the incineration.   The method for treating radioactive cesium contaminants according to claim 1, wherein the incinerator is a rotary kiln equipped with a sodium chloride spray nozzle for spraying sodium chloride toward the furnace.   A rotary kiln is rotatably supported by a horizontal rotary drum, a sealed outer shell covering the outer periphery of the rotary kiln, a radioactive waste input section that passes through the outer shell and reaches one end of the rotary drum, An exhaust gas outlet part connected to the other end, and the radioactive waste input part and the exhaust gas outlet part are airtightly flange-connected to the outer shell, respectively, and the exhaust gas outlet part has a flame in the rotary drum. 3. A method for treating radioactive cesium contaminants according to claim 2, wherein a burner for burning radioactive waste is provided, and an incineration residue discharge port is provided at the bottom of the exhaust gas outlet.   4. The method for treating radioactive cesium contaminants according to claim 3, wherein the rotary kiln is further connected to the incineration residue discharge port with a stoker portion whose outer periphery is covered with a sealed outer shell.

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