JPH1026696A - Method for plasma melting treatment of radioactive solid waste and facility used for such method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent chlorine from coming in contact with cesium oxide in a slag layer to capture volatile cesium during the fusion and solidification of it. SOLUTION: In a plasma melting treatment method where radioactive solid wastes 3 are melted by plasma heating, a plasma melting treatment is carried out after the radioactive solid wastes 3 are preheated both at 250 deg.C or higher and at a lower temperature than the boiling point of cesium, preferably at 300 deg.C to 400 deg.C. Plasma melting treatment facility is provided with a preheating component 2 which preheats the solid wastes 3 to a prescribed temperature before they are loaded into a plasma melting furnace 1 and is equipped with an exhaust means 6 for extracting a generated gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for plasma melting of radioactive solid waste generated at a nuclear power plant or the like, for example, low-level radioactive solid waste, and a plasma melting processing facility used for the method. More specifically, the present invention relates to a plasma melting treatment method for radioactive solid waste and a plasma melting treatment equipment used for preventing environmental release due to volatilization during plasma melting treatment of a cesium compound contained in radioactive solid waste. is there.

[0002]

2. Description of the Related 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 of performing melting treatment by plasma heating has been studied. According to this method, low-level radioactive solid waste can be collectively melt-processed without separation, so that the cost required for waste treatment can be reduced, and the radioactive nuclide cesium in the slag layer This is advantageous from the viewpoint of radiation protection.

[0003]

However, various types of low-level radioactive waste generated in nuclear power plants and the like are mixed, and radioactively contaminated vinyl chloride is discarded as waste. There is. When low-level radioactive waste containing vinyl chloride is melted at once,
There is a problem that cesium oxide trapped 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 form chloride. Cesium chloride is considered to be easily dissociated and volatilized in the slag layer, which is an ionic melt, due to its ionic bonding property. This is an obstacle to the practical use of the plasma melting treatment method.

FIG. 2 shows the results of a melting test performed assuming the treatment of low-level radioactive solid waste. This is a result obtained when a French CAE (French Atomic Energy Agency) melts a sample simulating radioactive waste generated from a fuel reprocessing step or the like together with a simulated nuclide by plasma heating (cited reference: H. Massit). , G.Naud, R.Atabek andW.
Hoffelner, "Evaluation of the plasma centrifugal pr
ocess for radioactive waste treatment ", Internation
al Incinaeration Conference, May 1995, USA). As samples, three types of simulated wastes A, B, and C with different mixing ratios of vinyl chloride, polyethylene, cellulose, etc., ash (ash) generated from waste treatment facilities, and ion exchange resin are used. . The line graph shows the weight ratio (wt%) of chlorine contained in the molten sample, and the bar graph shows the weight ratio (wt%) of cesium transferred to the slag layer after melting. As is clear from the figure, when the weight percentage of chlorine contained in the molten sample increases from 6% to 19%, the percentage of Cs (cesium) trapped in the slag layer drops significantly from 22% to 4%. You can see that it is. That is, it is clear that when the chlorine concentration in the molten sample is high, the transfer rate of cesium to the slag layer decreases.

Although it has been pointed out that cesium is easily volatilized by waste containing chlorine,
No effective countermeasures have been taken so far, and there is a demand for the development of effective countermeasure technologies for the practical use of the plasma melting treatment method.

The present invention relates to a plasma melting treatment method for radioactive solid waste capable of preventing contact of chlorine with a slag layer in order to trap volatile cesium during solidification, and a plasma melting treatment equipment used therefor. The purpose is to provide.

[0007]

Means for Solving the Problems In order to achieve the above object, the invention according to claim 1 provides a method for plasma melting a radioactive solid waste by melting the radioactive solid waste by plasma heating. After preheating at a temperature of 250 ° C. or higher and lower than the boiling point of cesium, the plasma heating and melting treatment is performed.

That is, chlorine contained in vinyl chloride or the like is 2
It is considered that chlorine starts to be released as a gas component at 50 ° C., and when the temperature is 300 ° C. or more, the speed at which chlorine is released from vinyl chloride or the like becomes a sufficient speed. This temperature is the boiling point of cesium (eg, the boiling point of cesium is 760 ° C.)
It is much lower temperature than. On the other hand, when the boiling point of cesium is reached, cesium evaporates and the effect on dechlorination is not much different from that at 400 ° C. Therefore, before the plasma melting treatment, the radioactive solid waste is preheated at a temperature of 250 ° C. or higher and lower than the boiling point of cesium, preferably at 300 to 400 ° C. as described in claim 2, whereby the chloride in the radioactive solid waste is heated. 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.

Therefore, even if the plasma melting treatment is carried out in a state containing vinyl chloride or the like without separating the radioactive solid waste, no chlorine is generated during the plasma melting treatment, or the amount of chlorine is extremely reduced. In addition, cesium oxide trapped in the slag layer is less likely to become chloride and dissociate and volatilize.

[0010] Further, in the invention according to claim 3, the waste is preheated by the heat of the exhaust gas from the plasma melting furnace. In this case, the heat generated in the plasma melting process can be effectively used.

Further, the plasma melting treatment equipment according to claim 4 preheats the radioactive solid waste before being introduced into the plasma melting furnace to a temperature of 250 ° C. or higher and lower than the boiling point of cesium, and removes generated gas. A preheating unit having an exhaust unit is provided. In this case, it is possible to continuously perform chlorine extraction and plasma melting treatment by preheating the waste.

Further, according to the present invention, the exhaust gas of the plasma melting furnace is exhausted together with the gas generated in the preheating section through the preheating section, so that the exhaust gas from the plasma melting furnace is used as a heat source of the preheating section. ing. In this case, the chlorine gas generated in the preheating section 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 cesium trapping rate.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below in detail based on the best mode shown in the drawings.

FIG. 1 shows the concept of a plasma melting treatment facility according to an embodiment in which the present invention is applied to a method for plasma melting treatment of low-level radioactive solid waste. In front of the inlet of the plasma melting furnace 1, a preheating unit 2 provided with an exhaust gas treatment device 6 as an 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. Further, the exhaust gas treatment device 6 is connected to, for example, an end of the preheating unit 2 remote from the plasma melting furnace 1, and the high temperature exhaust gas generated in the plasma melting furnace 1 is guided into the preheating unit 2 and then preheated. 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 the exhaust gas heat is recovered. The solid waste 3 is heated by the exhaust gas from the plasma melting furnace 1 or by the external preheating device 8 or by both heats to a temperature of 250 ° C. or more and less than the boiling point of cesium, for example, less than 760 ° C., preferably 300 to 400 ° C. Preheated to the range. The solid waste 3 into the plasma melting furnace 1
Is first charged into the preheating unit 2 by the charging device 7 and then subjected to a predetermined preheat treatment, followed by gravity drop or continuous feeding to the plasma furnace 1 by an appropriate amount by a known feeding means or supply means.

In the figure, reference numeral 4 denotes a plasma torch for generating a plasma arc, 5 a solidifying device for solidifying the molten metal, and 9 a molten metal in which the solid waste 3 is melted.

The plasma melting treatment method of the present invention using the plasma melting treatment equipment configured as described above is carried out as follows. Needless to say, the plasma melting treatment method of the present invention can be carried out with equipment other than the plasma melting treatment equipment shown in FIG.

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 of 250 ° C. or higher and lower than the boiling point of cesium while passing through the preheating unit 2, that is, a temperature at which cesium contained in the waste 3 is not evaporated. Is done. here,
The reason for setting the preheating temperature of the solid waste 3 to 250 ° C. or higher is to extract chlorine as a gaseous component from vinyl chloride contained in the solid waste 3. If the temperature is lower than this temperature, chlorine does not escape as a gaseous component. Because. On the other hand, waste 3
The preheating temperature is set to a temperature lower than the boiling point of cesium in order to prevent cesium from evaporating in the preheating unit 2. Dechlorination is started even at a preheating temperature of 250 ° C., but at 300 ° C. or higher, chlorine escape occurs at a sufficiently high processing rate. Also,
If the temperature exceeds 400 ° C., it is considered that chlorine hardly remains in vinyl chloride or the like. In the vicinity of the boiling point of cesium, the dechlorination effect is not much different from that at 400 ° C. despite the possibility of cesium evaporation. Therefore, in this embodiment,
The solid waste 3 is preheated in the range of 300C to 400C. Of course, it is possible to preheat to a higher temperature, and in that case, the preheating time can be shortened.
Although it does not prevent preheating to a high temperature exceeding ℃, increasing the preheating temperature to near the boiling point of cesium is not preferable from the viewpoint of preventing cesium evaporation.
In addition, it is preferable that the preheating takes a time necessary for sufficiently extracting chlorine contained in the vinyl chloride, and the size, the mounting position, and the like of the vinyl chloride contained in the solid waste 3 are preferable.
Although it depends on the shape, etc., the point is that the solid waste 3 is 300
It is sufficient if the heating is performed at a temperature of from 400C to 400C.

Here, when the preheating of the solid waste 3 cannot be achieved only by the heat of the exhaust gas from the plasma melting furnace 1, the preheating may be assisted by the preheating device 8. 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 becomes a gaseous component. Get out of.

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. Then, the solid waste 3 is collectively arc-heated and melted while containing vinyl chloride, and cesium in the solid waste is captured in the slag layer. At this time, since chlorine has already been removed from the vinyl chloride contained in the solid waste 3 as a gaseous component, the cesium oxide captured in the slag layer does not dissociate as chloride and volatilize. Therefore, even if the solid waste 3 is melted by plasma heating while containing a chlorine-containing substance such as vinyl chloride, the capture rate of cesium does not decrease.

The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and can be variously modified without departing from the gist of the present invention. For example, in the above description, the preheating in the preheating unit 2 is performed using the heat of the exhaust gas from the plasma melting furnace 1, but the exhaust gas from the plasma melting furnace 1 is directly heated by another exhaust gas processing apparatus. Exhaust from 1 and preheat section 2
May be heated only by a heating device. Further, the exhaust gas from the plasma melting furnace 1 can be used as a heat source through a heat exchanger installed in the preheating unit 2.

A series of plasma melting processes does not necessarily need to be performed continuously in a facility provided with a preheating unit 2 separately from the plasma melting furnace 1.
It is also possible to perform a batch process in which after preheating to the above preheating temperature, extracting chlorine as a gas component and exhausting, and then performing a melting process by plasma heating.

Further, the preheating temperature of the solid waste 3 is not necessarily limited to the above-mentioned range of 300 ° C. to 400 ° C., and it is necessary to prevent the cesium contained in the solid waste 3 from being vaporized and to vaporize chlorine. Any temperature can be used.

[0023]

As described above, the method for plasma-melting radioactive solid waste according to the first aspect of the present invention comprises preheating the radioactive solid waste at a temperature of 250 ° C. or higher and lower than the boiling point of cesium, and then performing the plasma melting process. Therefore, even if the solid waste contains a chlorine-containing substance such as vinyl chloride and is melted, the chlorine reacts with the cesium oxide trapped in the slag layer during the plasma melting process, resulting in chloride. It does not volatilize as a substance. Therefore, even if radioactive solid waste generated from a nuclear power plant, for example, low-level radioactive solid waste is melted as it is without removing chlorine-containing substances such as vinyl chloride, volatile radioactive nuclides can be stably converted into a slag layer. To prevent the radioactive material from being released into the environment, thereby further contributing to the protection of radiation. That is,
Practical application of melting treatment of radioactive solid waste by plasma heating.

In addition, since it is possible to omit the pretreatment for separating chlorine-containing substances such as vinyl chloride, it is possible to maximize the advantage of the plasma melting treatment method in which radioactive solid waste can be collectively melted. It can be used for

Further, since cesium is also a key nuclide in the scaling factor method applied prior to final disposal of the waste, it is useful for confirming the radioactivity of the waste. In particular, as described in claim 2, when preheating at 300 ° C to 400 ° C, the most stable dechlorination can be performed in a good processing time.

Further, in the plasma melting treatment method according to the third aspect, since the preheating is performed by the heat of the exhaust gas from the plasma furnace, the heat efficiency of the plasma melting treatment equipment can be improved by exhaust heat recovery.

Further, the plasma melting treatment equipment according to claim 4 preheats the radioactive solid waste before being introduced into the plasma melting furnace to a temperature of 250 ° C. or higher and lower than the boiling point of cesium, and removes generated gas. Since the preheating section provided with the exhaust means is provided, it is possible to continuously perform chlorine extraction and plasma melting processing by preheating solid waste.

Further, according to a fifth aspect of the present invention, the exhaust gas from the plasma melting furnace is used as a heat source of the preheating section by exhausting the exhaust gas of the plasma melting furnace through the preheating section together with the gas generated in the preheating section. As a result, the chlorine gas generated in the preheating section 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 cesium trapping rate.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an example of a facility for performing a plasma melting treatment 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 a slag layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plasma melting furnace 2 Preheating part 3 Radioactive solid waste 6 Exhaust gas treatment device as exhaust means of preheating part 8 Preheating device of preheating part

Claims (5)

[Claims] 1. A method for plasma melting a radioactive solid waste in which radioactive solid waste is melted by plasma heating, wherein said radioactive solid waste is preheated to a temperature of 250 ° C. or higher and lower than the boiling point of cesium, and then said plasma heating is performed. A plasma melting treatment method for radioactive solid waste, comprising performing a melting treatment. 2. The method according to claim 1, wherein the preheating is performed at a temperature of 300 ° C.
2. The temperature at which the temperature reaches to 400 [deg.] C.
A method for plasma melting of radioactive solid waste according to the above. 3. The method according to claim 1, wherein the preheating is performed using heat of exhaust gas from a plasma melting furnace. 4. A radioactive solid waste plasma melting treatment facility for melting radioactive solid waste by plasma heating, wherein the radioactive solid waste before being introduced into a plasma melting furnace is at least 250 ° C. and less than the boiling point of cesium. A radioactive solid waste plasma melting treatment facility, comprising: a preheating section provided with an exhaust means for preheating to a temperature and extracting generated gas. 5. An exhaust gas from the plasma melting furnace is used as a heat source of the preheating unit by exhausting exhaust gas from the plasma melting furnace together with gas generated in the preheating unit through the preheating unit. A plasma melting treatment facility for radioactive solid waste according to claim 4.