JPH077108B2 - Method for melting and solidifying radioactive waste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to the production of radioactive waste with a low melting point metal or metal compound having a radiation shielding effect or an attenuation effect such as lead oxide or antimony oxide by microwave heating. The present invention relates to a method of solidifying.

[Prior Art] Wastes containing radioactive substances are generated from nuclear reactors, reprocessing facilities, nuclear fuel facilities, and the like. Such radioactive waste is solidified for safer storage and safe disposal.

As a method for solidifying radioactive waste, a solidifying method using cement, asphalt, plastic, glass or the like is performed.

[Problems to be Solved by the Invention] In the cement solidification method, since the solidification can be carried out at room temperature, the apparatus is simple and the operation is easy, and the advantage is that it can be carried out at a relatively low cost, but on the other hand, cement and sand etc. serve as extenders. It has a drawback that the volume and weight become extremely large, and the space and cost for transportation and final storage become large.

Although the asphalt solidification method and the plastic solidification method have the advantage that they can be operated at relatively low temperatures, asphalt and plastic become the bulking agent, if not as much as the cement solidification method, and they have almost no radiation attenuation effect and fire It has the major drawback of being weak.

Further, the vitrification method requires a considerably high temperature for vitrification, and has a drawback that the radiation shielding effect is small. In addition, there is a drawback that the ratio of the glass molding agent addition required for vitrification of high-level waste liquid is large. For example, a typical ratio is about 70% by weight of the glass forming agent to 30% by weight of the radioactive liquid waste. This is because the glass forming agent has a poor heat transfer efficiency, and if the ratio is smaller than this, it becomes difficult to remove the decay heat in a solidified body of a practical scale, and the temperature rises significantly.

The object of the present invention is to solve the above-mentioned drawbacks of the prior art, to be able to safely melt and solidify at a relatively low temperature, to have a high radiation shielding effect or attenuation effect, and also to have a high heat transfer and heat dissipation effect. It is an object of the present invention to provide a method for melting and solidifying radioactive waste, which has a far greater volume reduction effect than technology.

[Means for Solving the Problems] The present invention capable of achieving the above-mentioned object is to provide a low melting point metal or metal compound having a radiation shielding effect or an attenuation effect as a solidifying agent to be mixed with radioactive waste. There is a major feature in using it, after supplying them into a crucible made of metal, applying microwaves to heat and melt,
After that, it is a solidification treatment method in which it is cooled and solidified.

The low melting point metal or metal compound is, for example, metal lead, lead oxide, antimony oxide, bismuth oxide, etc.
A powder or granules of a substance having a melting point of ℃ or less or a working temperature is used.

[Operation] By applying a microwave, the above-mentioned object to be processed is melted at a relatively low temperature, and then cooled to obtain a stable solidified body.

The metal or metal compound having a low melting point as described above has a high radiation attenuation effect, and particularly when metal lead or lead oxide is used, a very good radiation shielding effect can be obtained. Further, since the heat transfer property is also good, self-heating due to the decay heat generated inside the solidified body is promptly dissipated to the outside, and the rise in the internal temperature can be suppressed.

According to the present invention, for example, about 70% by weight of radioactive waste liquid is used.
A good solidified product can be obtained by using 30 wt% of a low melting point metal or metal compound.

[Embodiment] FIG. 1 is a flowchart showing an example of a melting and solidifying treatment step according to the present invention. Liquid or solid radioactive waste and powder or granules of a low melting point metal or metal compound having a radiation shielding effect or an attenuation effect are made of metal in the microwave melting furnace 14 by the corresponding supply devices 10 and 12, respectively. Supplied in crucible. Here, the low melting point metal or metal compound is a substance having a melting point or working temperature of about 1000 ° C. or lower, such as metallic lead, lead oxide, antimony oxide, and bismuth oxide. As the crucible made of metal, for example, a crucible made of stainless steel, or a crucible made of stainless steel with a ceramic lining inside is used. The microwave melting furnace 14 may be a continuous furnace or a batch furnace. The inside of the melting furnace 14 is heated by the microwave applied from the microwave oscillator 16 to a temperature equal to or higher than the melting point or working temperature of the low melting point metal or metal compound used. As a result, the radioactive waste in the crucible made of metal and the metal or metal compound having a low melting point are heated and melted and uniformly mixed, and then cooled to obtain a good solidified body.

FIG. 2 shows an example of a cross section of the melted and solidified body. Here, the crucible 20 made of metal is made of stainless steel and has a ceramic lining 22 on its inner surface. While the low melting point metal or metal compound 24 is solidified, the radioactive waste 26 is dispersed and buried. Of course, it is possible that a mixed substance or a compound substance depending on the contained substance is generated at the boundary between the low melting point metal or metal compound 24 and the radioactive waste 26. In this way, the radioactive waste 26 has a structure in which it is covered with the low melting point metal or metal compound 24 and solidified, and a stable solidified body is obtained.

In the present invention, a crucible made of metal is used because it can prevent microwave leakage. Further, the microwave heating efficiency can be further improved by providing a ceramic lining on the inside.

Next, an example of an experiment in which sodium carbonate was used as a simulated waste instead of radioactive waste and solidified was described.

[Experimental Example] A sample containing 70% by weight of sodium carbonate and 30% by weight of lead oxide was continuously supplied into a 5 kW microwave melting furnace using a microwave of 2450 MHz, and microwave was applied. And heated to about 830-900 ° C. This melts the material to be treated, and then cools and solidifies it to 4 kg per hour.
It was possible to obtain a solidified body of. This solidified product was extremely stable even when left in the air for a long time.

When the amount of lead oxide, which has a low melting point, is gradually increased from a small weight% value to form a solidified body, it is exposed to air (in a room at 20 ° C).
It can be found that it does not deliquesce even if left for 30 days. That is 30% by weight of lead oxide and 70% by weight of radioactive waste.

The amount of lead oxide having a low melting point may be further increased, but the amount is increased, which is not preferable.

EFFECTS OF THE INVENTION Since the present invention uses a metal or metal compound having a low melting point as a substance for solidifying radioactive waste as described above, stable melting is achieved by heating at a relatively low temperature of about 1000 ° C. or less. It has an excellent effect that a solidified body can be produced.

Since a substance having a radiation shielding effect or a high radiation attenuation effect is used as a metal or metal compound having a low melting point, the solidified product obtained has a radiation shielding effect and also has a high heat transfer effect, and therefore is based on decay heat. Even waste that is self-heated can efficiently dissipate the heat generated inside and can suppress the temperature rise.

Further, the present invention has an extremely high volume reduction effect by using a metal or metal compound having a low melting point, and is excellent in that the volume can be reduced by less than half as compared with the conventional vitrification treatment method. It has an effect.

[Brief description of drawings]

FIG. 1 is a flow chart showing an embodiment of a method for melting and solidifying radioactive waste according to the present invention, and FIG. 2 is an explanatory view showing an example of a solidified body obtained thereby. 10,12 …… Supply device, 14 …… Microwave melting furnace, 16 ……
Microwave oscillator, 20 ... Stainless steel crucible, 22
…… Ceramic lining, 24 …… Low melting point metal or metal compound, 26 …… Radioactive waste.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideaki Tamai, 1500 1500, Osaka, Kamifukuoka, Saitama Prefecture 23, Kawagoe Manufacturing Co., Ltd., Nippon Radio Co., Ltd. (72) Ikuro Kisanuki, 1500, Fukuoka 23, Kamifukuoka, Saitama (56) References JP 55-80735 (JP, A)

Claims (1)

[Claims] 1. A crucible made of metal, radioactive waste containing one or more kinds of powder or granules selected from metallic lead, lead oxide, antimony oxide, and bismuth oxide, and radioactive waste consisting of sodium salt. The powder or granules are supplied in a ratio of about 30% by weight with respect to about 70% by weight, and the mixture is heated and melted at a temperature of about 1000 ° C or less by applying a microwave, and then cooled and solidified. Method for melting and solidifying radioactive waste.