JP3764528B2 - Plasma melting treatment method for radioactive solid waste and plasma melting treatment equipment used therefor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plasma melting treatment method for radioactive solid waste generated at a nuclear power plant or the like, for example, low-level radioactive solid waste, and a plasma melting treatment facility used therefor. More specifically, the present invention relates to a method for plasma melting treatment of radioactive solid waste and a plasma melting treatment equipment used therefor, which prevent environmental release due to volatilization during plasma melting treatment of cesium compounds contained in radioactive solid waste. is there.
[0002]
[Prior art]
As a method for treating radioactive solid waste discharged from a nuclear power plant or the like, for example, low-level radioactive solid waste, a technique for performing melting treatment by plasma heating has been studied. In this method, low-level radioactive solid waste can be melt-processed in a batch without separation, and the cost required for waste treatment can be reduced, and the radioactive nuclides in the slag layer of cesium This is advantageous from the viewpoint of radiation protection.
[0003]
[Problems to be solved by the invention]
However, various types of low-level radioactive waste generated at nuclear power plants and the like are mixed, and radioactively contaminated vinyl chloride may be discarded as waste. When low-level radioactive waste containing vinyl chloride is melted together, there is a problem that cesium oxide captured in the slag layer is volatilized by chlorine contained in vinyl chloride. That is, cesium trapped in the slag layer as an oxide during the plasma melting process reacts with chlorine to become chloride. It is considered that cesium chloride is easily bonded and volatilized in the slag layer, which is an ionic melt, because it is ion-bonded. This is an obstacle to the practical application of the plasma melting treatment method.
[0004]
FIG. 2 shows the results of a melting test conducted assuming the treatment of low-level radioactive solid waste. This is the result obtained when French CAE (French Atomic Energy Agency) melts a sample simulating radioactive waste generated from the fuel reprocessing process etc. by plasma heating together with a simulated nuclide (cited reference: H. Massit , G. Naud, R. Atabek and W. Hoffelner, "Evaluation of the plasma centrifugal process for radioactive waste treatment", International Incinaeration Conference, May 1995, USA). As samples, three types of simulated waste of A, B and C with different mixing ratios such as vinyl chloride, polyethylene and cellulose, ash generated from waste treatment facilities, etc. and ion exchange resin are used. . The line graph indicates the weight ratio (wt%) of chlorine contained in the molten sample, and the bar graph indicates the weight ratio (wt%) of cesium transferred to the slag layer after melting. As is apparent from the figure, when the weight ratio of chlorine contained in the molten sample is increased from 6% to 19%, the ratio of Cs (cesium) trapped in the slag layer is greatly reduced from 22% to 4%. I understand that That is, it is clear that the migration rate of cesium to the slag layer decreases when the chlorine concentration in the molten sample is high.
[0005]
Thus, although it has been pointed out that cesium is likely to be volatilized by waste containing chlorine, effective measures have not been taken so far, and it is effective for practical use of the plasma melting treatment method. Development of countermeasure technology is demanded.
[0006]
The present invention provides a method for plasma melting treatment of radioactive solid waste capable of preventing contact between chlorine and a slag layer in order to trap volatile cesium during melt solidification, and a plasma melting treatment equipment used for the method. With the goal.
[0007]
[Means for Solving the Problems]
In order to achieve this object, the invention according to claim 1 is a method for plasma melting treatment of radioactive solid waste in which the radioactive solid waste is melted by plasma heating, wherein the radioactive solid waste is 250 ° C. or higher and lower than the boiling point of cesium. The plasma heating and melting treatment is performed after preheating at a temperature of 10% and extracting chlorine in the radioactive solid waste as a gas component .
[0008]
That is, chlorine contained in vinyl chloride begins to escape as a gas component at 250 ° C., and when it exceeds 300 ° C., the rate at which chlorine escapes from vinyl chloride is sufficient, and in temperatures exceeding 400 ° C. Seems to have little chlorine left. This temperature is sufficiently lower than the boiling point of cesium (for example, the boiling point of cesium is 760 ° C.). On the other hand, when the boiling point of cesium is reached, evaporation of cesium occurs and the influence on dechlorination is not much different from that at 400 ° C. Therefore, if the radioactive solid waste is preheated at a temperature of 250 ° C. or higher and lower than the boiling point of cesium, preferably 300 to 400 ° C. as described in claim 2, before the plasma melting treatment, chlorination in the radioactive solid waste is performed. Chlorine contained in vinyl or the like is extracted as a gas component. Here, the preheating time is not particularly important, and it is sufficient if the solid waste is heated to 300 ° C to 400 ° C.
[0009]
Therefore, even if the plasma melting process is performed in a state containing vinyl chloride without separating the radioactive solid waste, chlorine is not generated during the plasma melting process, or the amount of chlorine is extremely reduced, and the slag layer The cesium oxide trapped in is reduced to dissociate and volatilize as chloride.
[0010]
According to the invention described in claim 3, waste preheating is performed by the heat of the exhaust gas from the plasma melting furnace. In this case, the heat generated by the plasma melting process can be used effectively.
[0011]
Further, in the plasma melting processing facility according to claim 4, the radioactive solid waste before being put into the plasma melting furnace is preheated to a temperature of 250 ° C. or higher and lower than the boiling point of cesium and generated from the radioactive solid waste . A preheating part provided with exhaust means for extracting chlorine gas is provided. In this case, the extraction of chlorine by preheating the waste and the plasma melting process can be performed continuously.
[0012]
Further, in the invention described in claim 5, the exhaust gas from the plasma melting furnace is exhausted together with the chlorine gas generated from the radioactive solid waste in the preheating part through the preheating part, so that the exhaust gas from the plasma melting furnace is used as a heat source for the preheating part. I am trying to use it. In this case, the chlorine gas generated in the preheating part does not flow back to the plasma melting furnace side, and the reaction between cesium oxide and chlorine trapped in the slag layer is reliably prevented to increase the capture rate of cesium.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the configuration of the present invention will be described in detail based on the best mode shown in the drawings.
[0014]
FIG. 1 shows a concept of a plasma melting treatment facility, which is an embodiment in which the present invention is applied to a plasma melting treatment method for low-level radioactive solid waste. In front of the inlet of the plasma melting furnace 1, a preheating unit 2 having an exhaust gas treatment device 6 as exhaust means is provided. The preheating unit 2 is provided, for example, at a position higher than the plasma melting furnace 1, and is provided so that the gas generated in the preheating unit 2 is less likely to flow into the plasma melting furnace 1 side. The exhaust gas treatment device 6 is connected to, for example, the end of the preheating unit 2 away from the plasma melting furnace 1 and preheats after the high temperature exhaust gas generated in the plasma melting furnace 1 is introduced into the preheating unit 2. It is provided so as to be discharged together with the gas generated in the section 2. Therefore, the low-level radioactive solid waste (hereinafter simply referred to as solid waste) 3 is preheated in the preheating unit 2 by the exhaust gas from the plasma melting furnace 1, and exhaust gas heat recovery is performed. The solid waste 3 is heated to 250 ° C. or more and less than the boiling point of cesium, for example, less than 760 ° C., preferably 300 to 400 ° C., by the exhaust gas from the plasma melting furnace 1, by the external preheating device 8, or by the heat of both. Preheated to a range of Further, the solid waste 3 is charged into the plasma melting furnace 1 after being first charged into the preheating unit 2 by the charging device 7 and then subjected to a predetermined pre-heat treatment and then dropped by gravity or by a known feeding means or supplying means. An appropriate amount is continuously sent to the furnace 1.
[0015]
In the figure, reference numeral 4 is a plasma torch for generating a plasma arc, 5 is a solidifying device for solidifying the molten metal, and 9 is a molten metal in which the solid waste 3 is melted.
[0016]
The plasma melting processing method of the present invention is carried out as follows using the plasma melting processing equipment configured as described above. Of course, the plasma melting treatment method of the present invention can be implemented in facilities other than the plasma melting processing facility of FIG.
[0017]
First, the low-level radioactive solid waste 3 discharged from a nuclear power plant or the like is sent into the preheating unit 2 by the charging device 7. The solid waste 3 is preheated to a temperature that is 250 ° C. or higher and lower than the boiling point of cesium while passing through the preheating unit 2, that is, a temperature that does not evaporate cesium contained in the waste 3. Is done. Here, the reason why the preheating temperature of the solid waste 3 is set to 250 ° C. or more is to extract chlorine as a gaseous component from vinyl chloride contained in the solid waste 3, and when the temperature is lower than this temperature, the chlorine is a gaseous component. It is because it does not come off as. On the other hand, the reason why the preheating temperature of the waste 3 is set to a temperature lower than the boiling point of cesium is to prevent evaporation of cesium in the preheating portion 2. Dechlorination is started even at a preheating temperature of 250 ° C., but chlorine escape occurs at a sufficiently high processing speed at 300 ° C. or higher. In addition, it is considered that almost no chlorine remains in vinyl chloride at temperatures exceeding 400 ° C, and the dechlorination effect is much different from that at 400 ° C despite the possibility of evaporation of cesium near the boiling point of cesium. Absent. Therefore, in this embodiment, the solid waste 3 is preheated in the range of 300 ° C to 400 ° C. Of course, it is possible to preheat to a higher temperature, and in that case, the preheating time can be shortened, so that preheating to a high temperature exceeding 400 ° C. is not prevented, but the preheating temperature is reduced to near the boiling point of cesium. Raising is not preferable from the viewpoint of preventing evaporation of cesium. In addition, it is preferable that the preheating takes time necessary for sufficiently extracting chlorine contained in the vinyl chloride, and it depends on the size, mounting position, shape, etc. of the vinyl chloride contained in the solid waste 3. As long as the solid waste 3 is heated to 300 ° C. to 400 ° C., it is sufficient.
[0018]
Here, when the preheating of the solid waste 3 is not achieved only by the heat of the exhaust gas from the plasma melting furnace 1, the preheating device 8 may assist the preheating. In this way, the solid waste 3 is preheated to the above-mentioned temperature in the preheating unit 2, whereby chlorine contained in vinyl chloride or the like in the solid waste 3 becomes a gaseous component and the solid waste 3 Get out of it.
[0019]
When the chlorine is sufficiently removed from the vinyl chloride contained in the solid waste 3, the solid waste 3 is put into the plasma melting furnace 1. And the solid waste 3 is collectively arc-heated in the state containing vinyl chloride, it is melt-processed, and the cesium in a solid waste is capture | acquired by the slag layer. At this time, since chlorine is already extracted as a gaseous component from the vinyl chloride contained in the solid waste 3, the cesium oxide trapped in the slag layer does not dissociate and volatilize as chloride. Therefore, even if the solid waste 3 is melted by plasma heating while containing a substance containing chlorine such as vinyl chloride, the capture rate of cesium does not decrease.
[0020]
The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the scope of the present invention. For example, in the above description, the heat of the exhaust gas from the plasma melting furnace 1 is used to perform preheating in the preheating unit 2, but the exhaust gas from the plasma melting furnace 1 is directly processed by another exhaust gas processing apparatus. The preheating unit 2 may be heated only by a heating device. It is also possible to use the exhaust gas from the plasma melting furnace 1 as a heat source through a heat exchanger installed in the preheating unit 2.
[0021]
In addition, the series of plasma melting processes does not necessarily need to be continuously performed with the equipment provided with the preheating unit 2 separately from the plasma melting furnace 1, and is first preheated to the above preheating temperature in the existing plasma melting furnace 1. Then, after extracting chlorine as a gas component and exhausting it, a batch process of performing a melting process by plasma heating is also possible.
[0022]
Furthermore, the preheating temperature of the solid waste 3 is not necessarily limited to the above-described range of 300 ° C. to 400 ° C., and it is possible to prevent vaporization of cesium contained in the solid waste 3 and vaporize chlorine. Any temperature is acceptable.
[0023]
【The invention's effect】
As described above, in the method for plasma melting treatment of radioactive solid waste according to claim 1, the radioactive solid waste is preheated at a temperature of 250 ° C. or higher and lower than the boiling point of cesium to remove chlorine in the radioactive solid waste. Since the plasma melting process is performed after extraction as a gas component , chlorine is trapped in the slag layer during the plasma melting process even if the solid waste contains a substance containing chlorine such as vinyl chloride. It does not react with cesium oxide and volatilize as chloride. Therefore, even if radioactive solid waste generated from nuclear power plants, for example, low-level radioactive solid waste is directly melted without removing chlorine-containing substances such as vinyl chloride, volatile radionuclides are stably removed from the slag layer. And can contribute to the protection of radiation by preventing the release of radioactive substances into the environment. That is, the melting treatment of radioactive solid waste by plasma heating can be put into practical use.
[0024]
In addition, pretreatment for separating chlorine-containing substances such as vinyl chloride can be omitted, so that the advantages of the plasma melting method can be maximized because radioactive solid waste can be melted together. Can do.
[0025]
Furthermore, cesium is a key nuclide of the scaling factor method applied before the final disposal of the waste, so it helps to confirm the radioactive content of the waste. In particular, as described in claim 2, when preheating is performed at 300 ° C. to 400 ° C., the most stable dechlorination can be performed in a good processing time.
[0026]
In the plasma melting treatment method according to the third aspect, since preheating is performed with the heat of the exhaust gas from the plasma furnace, the heat efficiency of the plasma melting treatment facility can be improved by exhaust heat recovery.
[0027]
Further, in the plasma melting processing facility according to claim 4, the radioactive solid waste before being put into the plasma melting furnace is preheated to a temperature of 250 ° C. or higher and lower than the boiling point of cesium and generated from the radioactive solid waste . Since the preheating part provided with the exhaust means which extracts chlorine gas is provided, the extraction of chlorine by the preheating of the solid waste and the plasma melting process can be carried out continuously.
[0028]
Further, in the invention described in claim 5, the exhaust gas from the plasma melting furnace is exhausted together with the chlorine gas generated from the radioactive solid waste in the preheating part through the preheating part, so that the exhaust gas from the plasma melting furnace is used as a heat source for the preheating part. Since it is used, chlorine gas generated in the preheating part does not flow back to the plasma melting furnace side, and the reaction between cesium oxide and chlorine trapped in the slag layer is surely prevented to trap cesium. Increase the rate.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing an example of a facility for implementing a plasma melting processing method to which the present invention is applied.
FIG. 2 is a graph showing the relationship between the chlorine content of radioactive waste and the transfer rate of cesium to the slag layer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Plasma melting furnace 2 Preheating part 3 Radioactive solid waste 6 Exhaust gas processing apparatus which is exhaust means of a preheating part 8 Preheating apparatus of a preheating part

Claims (5)

In the method for plasma melting treatment of radioactive solid waste, wherein the radioactive solid waste is melted by plasma heating, the radioactive solid waste is preheated at a temperature of 250 ° C. or higher and lower than the boiling point of cesium, and chlorine in the radioactive solid waste A plasma melting treatment method for radioactive solid waste, wherein the plasma heating and melting treatment is performed after extracting as a gaseous component .   The method for plasma melting treatment of radioactive solid waste according to claim 1, wherein the preheating is performed at a temperature at which the radioactive solid waste reaches 300 ° C to 400 ° C.   The method for plasma melting treatment of radioactive solid waste according to claim 1 or 2, wherein the preheating is performed by heat of exhaust gas from a plasma melting furnace. In a plasma melting treatment facility for radioactive solid waste that melts radioactive solid waste by plasma heating, the radioactive solid waste before being put into the plasma melting furnace is preheated to a temperature of 250 ° C. or higher and lower than the boiling point of cesium. A radioactive solid waste plasma melting treatment facility comprising a preheating unit provided with exhaust means for extracting chlorine gas generated from the radioactive solid waste. The exhaust gas from the plasma melting furnace is used as a heat source for the preheating part by exhausting the exhaust gas from the plasma melting furnace through the preheating part together with the chlorine gas generated from the radioactive solid waste in the preheating part. The facility for plasma melting treatment of radioactive solid waste according to claim 4.

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