JPH055078B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for treating radioactive waste liquid, which solidifies radioactive waste liquid discharged from a spent nuclear fuel reprocessing plant or the like. [Prior Art] Radioactive waste liquid discharged from spent nuclear fuel reprocessing plants, etc., particularly waste liquid with high levels of radioactivity, has conventionally been stored as waste liquid. In addition, in recent years, in order to make storage easier, a vitrification method has been developed in which the vitrified material is stored in a durable container made of stainless steel or the like called a canister. The conventional vitrification method will be explained with reference to Fig. 2: a. First, a glass raw material (e.g. glass cullet) is mixed with radioactive waste liquid 1, b. This is melted in a glass melting furnace 3, and then , c is poured out from the extraction nozzle 4 at the bottom into the canister 5. 6 in the figure indicates a glass flow. Also, 7 is the melting furnace 3
This shows the piping that delivers the steam generated inside to the processing equipment. [Problems to be Solved by the Invention] In the above conventional process, (a) the high temperature molten glass comes into direct contact with the inner surface of the canister; (b) This contact is carried out in an oxidizing atmosphere (air atmosphere). C. Since the molten glass is rapidly cooled and becomes crushed, the specific surface area of the solidified glass increases. There are other issues to improve. In addition, when replacing the canister to be filled,
The glass stream 6 must be interrupted, so that the molten glass passing through the nozzle 4 is intermittent. Therefore, the nozzle 4 is subjected to expansion and contraction due to temperature rise and fall, and the life of the nozzle 4 is shortened. There were also other problems. [Means for Solving the Problems] In order to solve the above problems, the present invention pours out the molten glass in the glass melting furnace into water to form a crushed material, and solidifies this under hydrothermal conditions. It is designed to be made into a frame, and after mixing the glass raw material with the radioactive waste liquid, it is heated to melt the glass raw material, and this melt is poured into water to form solidified glass in the form of crushed material. It is characterized by the fact that physical glass is heated and pressurized in the presence of water at a pressure of 70 kg/cm ² or more and a temperature of 150°C or more to form a skeleton, and then stored in a canister. The gist of this paper is a method for treating radioactive waste liquid. The present invention will be explained in more detail below. FIG. 1 is a system diagram showing a preferred embodiment of the present invention. In the method of the present invention, a glass raw material 2 is mixed with a radioactive waste liquid 1 and melted in a glass melting furnace 3. Radioactive waste liquid 1
Most of the radioactive substances inside are taken into the molten glass, and some of them are volatilized from the pipe 7 along with water vapor, but they are collected by a collection means (not shown) installed downstream of the pipe 7. Ru. The molten glass in the glass melting furnace 3 is poured into water 8, where it solidifies and is rapidly cooled to become fine crushed glass 9. After this crushed glass 9 is dried in a dryer 10, or after removing a required amount of adhering water with a drainer 11, it is formed into a skeleton under hydrothermal conditions and stored in a canister 5. The above series of processes will now be described in detail. Regarding the process: In the present invention, the radioactive waste liquid to be treated is not particularly limited, and in addition to waste liquid discharged from spent nuclear fuel reprocessing equipment, nuclear power plants,
It can be applied to various radioactive waste liquids, such as liquids discharged from research facilities. As glass raw materials, those containing silicic acid (SiO ₂ ) are used, such as borosilicate glass, soda borosilicate glass, soda lime borosilicate glass, soda lime glass, high lead silicate glass, phosphate-containing glass, etc. Silicate glass or the like may also be used. The mixing ratio of the glass raw material and the radioactive waste liquid is preferably 3 parts by weight or more, particularly about 3 to 10 parts by weight, of the glass raw material per 1 part by weight of the solid content in the radioactive waste liquid. Regarding the process: The temperature at which the glass raw material is melted may be a temperature at which the glass raw material has sufficient fluidity, and does not need to be particularly high. Steam generated from the glass melting furnace 3 and the dryer 10 is extracted through a pipe 7 and sent to collection and processing equipment. Regarding the process: The molten glass poured into water 8 is cooled and solidified, and is rapidly cooled to become a crushed material. This crushed glass is carried out by an appropriate means such as a bucket conveyor or a net conveyor, and sent to the next process. In addition, since the water 8 is heated and evaporated by the heat retained in the molten glass, it is preferable to replenish water according to the amount of evaporation. About the process: In this process, more water is removed from the crushed glass than is required in the subsequent hydrothermal solidification process. As this means, it is preferable to use either or both of the illustrated dryer 10 and draining device 11, but other means may also be used. About the process: The crushed glass fed from the process
After adding water as necessary, the glass is placed in a reaction stress container and heated under hydrothermal conditions to form the crushed glass into a skeleton. In the method of the present invention, in order to carry out the hydrothermal reaction, it is convenient to use an apparatus in which a compression piston is fitted to one or both ends of a cylindrical reaction vessel and a reaction filling chamber is formed in the center of the cylindrical vessel. be. That is, crushed glass to which water has been added is filled into this reaction filling chamber, and the filled material is compressed and heated by a compression piston to cause a hydrothermal reaction. If a canister is used as the reaction vessel, the effort of taking out the reaction vessel and filling it into the canister after the completion of the hydrothermal reaction can be saved. In addition, when carrying out this hydrothermal reaction, an alkali such as NaOH, KOH, Ca, etc. is added to the crushed glass.
(OH) ₂ , Sr(OH) ₂ , etc. may be mixed. In this way, the hydrothermal reaction that solidifies the crushed glass can be promoted. In the method of the present invention, when filling a reaction vessel with crushed glass, the crushed glass is divided into two or more parts, and each time one division is filled into the reaction vessel, a press (hereinafter referred to as "temporary press") is applied. ) is preferable. By temporarily pressing in this way, the amount of crushed glass filled in the reaction container is immediately compressed and its volume becomes smaller, so it is possible to fill a large amount of crushed glass into the reaction container. This makes it possible to reduce the capacity of the reaction vessel. This temporary pressing pressure may be lower than the pressure during the solidification reaction, and may be, for example, about 1/10 of the pressure during the solidification reaction. In addition, after filling all of the divided crushed glass into the reaction container, pressing was carried out using the pressure used during the solidification reaction without performing such a light temporary pressing.
It is enough to start the reaction. Therefore, in the method of the present invention, it is sufficient that the crushed glass is in a heated and pressurized state during the hydrothermal reaction, and the pressure is increased to a predetermined reaction pressure,
The temperature may be raised to a predetermined reaction temperature in advance of any one of these, or may be carried out simultaneously. In the present invention, the pressure of the hydrothermal reaction is 70 Kg/cm ² or more. The upper limit of pressure is practically 500Kg/cm ²
That's about it. Note that the pressure is naturally higher than the vapor pressure of water at the reaction temperature, so that a hydrothermal state is achieved. If the temperature of the hydrothermal reaction is lower than 150°C, the solidification reaction will not proceed and only a solidified product with extremely low strength will be obtained. A particularly preferred temperature is 200 to 350°C or higher. A hydrothermal reaction time of about 5 minutes to 2 hours is sufficient. If the pressure and temperature of the hydrothermal reaction are low, the reaction time will be long; on the other hand, if the pressure and temperature are high, the reaction time will be short. According to research conducted by the present inventors, it has been found that within the above pressure and temperature ranges, the strength of the obtained solidified product is higher when the material is maintained for a longer period of time under the lowest possible pressure and temperature conditions. Since the process shown in FIG. 1 shows an example of the method of the present invention, the method of the present invention is not limited to the process shown in FIG. [Operation] Solid content in radioactive waste liquid is sealed in glass. This glass is made by melting the glass and pouring it into water to create crushed glass, which is then formed into a frame through a hydrothermal reaction. , thus relatively cool glass contacts the canister.
The glass body filled in the canister has almost no cracks and has a small specific surface area. Further, since the molten glass can be continuously poured out from the glass melting furnace, the thermal shock to the nozzle 4 for pouring out the molten glass becomes extremely small. Furthermore, there is no need to provide a special pouring means such as the nozzle 4, and the molten glass can be allowed to overflow from the melting furnace 3 and poured into the water 8. In this way, the structure of the melting furnace 3 can be simple. [Examples] The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. Example 1 Borosilicate glass with an average particle size of 40 mm (composition is shown in Table-
1) The cullet 14.4Kg contains waste liquid from a nuclear fuel reprocessing plant.
60 was mixed, heated to 1100℃ to melt the borosilicate glass, and then poured into water to form Table 1.
The solidified radioactive glass shown in Fig. 1 was obtained. This was crushed to 120 meshes (0.125 mm) or less, and a solidification test was conducted. The results are shown in Figures 3 and 4. Figure 3 shows that 2 parts of water is added to 20 kg of vitrified material, and after thorough mixing, about 4 kg of this is charged into a pressurized reaction vessel with an inner diameter of 120 cm, and the pressure is 300 kg/
The relationship between the reaction temperature and the compressive strength is shown when the reaction is carried out at cm ² for 10 minutes. Figure 4 shows the relationship between reaction time and compressive strength when the same procedure was used but the reaction temperature was 270°C. Table 2 shows the analysis values of the obtained skeleton.

【table】

[Table] From FIGS. 3 and 4, it is clear that according to the method of the present invention, a frame with extremely high strength can be obtained. In particular, when pressurizing at 300Kg/ ^cm2 , the reaction temperature is
It is recognized that the strength can be significantly increased by setting the temperature to 270°C or higher and the reaction time to 10 minutes or more. Furthermore, when the obtained skeleton was stored in a stainless steel canister, no change occurred over time, and it was found that it could be stored stably for a long period of time. [Effect] As detailed above, in the present invention, the molten glass containing the solid content in the radioactive waste liquid is once poured into water to form crushed glass, and then subjected to a hydrothermal reaction to form a frame. The high temperature molten glass does not come into direct contact with the canister.
Therefore, the life of the canister can be extended. In addition, the specific surface area of the body is small, and the elution of metal ions and the like is minimal. Moreover, the volume of the frame becomes small. Furthermore, ordinary heating and pressurizing equipment is sufficient.
There is no need to use any other special equipment, and
Since additives are also inexpensive, running costs are also low. Furthermore, the structure of the glass melting furnace can be simplified and its lifespan can be extended.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing one procedure for implementing the present invention;
FIG. 2 is a system diagram showing a conventional example. Further, FIGS. 3 and 4 are graphs showing the measurement results in the example. 1...Radioactive waste liquid, 2...Glass raw material, 3...
Glass melting furnace, 8...water, 9...crushed glass.

Claims (1)

[Scope of Claims] 1. After mixing a glass raw material with a radioactive waste liquid, heating it to melt the glass raw material, pouring out the melt into water to form a solidified glass in the form of a crushed substance, and then converting the glass in the form of a crushed substance. is heated and pressurized in the presence of water at a pressure of 70 kg/cm ² or more and a temperature of 150°C or more to form a skeleton, and then stored in a canister. processing method. 2. The method for treating radioactive waste liquid according to claim 1, characterized in that a canister is used as a reaction vessel for holding the radioactive waste liquid glass in a heated and pressurized state to form a skeleton. 3. A method for treating radioactive waste liquid according to claim 1 or 2, characterized in that the crushed glass is mixed with an alkali to form a skeleton.