JPS6152440B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for solidifying radioactive waste, and more particularly to a method and apparatus for safely drying and solidifying radioactive waste.

The conventional method for disposing of liquid radioactive waste, which contains a large amount of solids, generated by nuclear power plants is to add cement or mortar and knead it to solidify it. Although the solidified cement obtained by this method is solidified and safe in handling, the radioactivity leaching rate with respect to water is not desirable and the volume reduction ratio is also poor.

Therefore, in recent years, it has been proposed to solidify with asphalt or plastic instead of cement. In particular, hardening with plastic
It is possible to obtain a solidified material with significantly superior volume reduction ratio and radioactive leaching rate. Solidifying agents for plastics are broadly classified into thermosetting resins and thermoplastic resins. However, plastics, which have excellent properties in terms of radioactivity leaching rate, are not compatible with water, and if waste contains water, the solidified material will only be brittle. , safety in handling is lost, and furthermore, if disposal at sea is assumed, the solidified material will become unsuitable due to decreased solidified material strength, increased radioactive leaching rate, etc.

Therefore, conventionally proposed treatment methods require two steps: drying and pulverizing radioactive waste using a dryer, and kneading the dried waste with plastic. Therefore, the following problems occur.

(1) Complexity of equipment is unavoidable.

(2) If the bubbles generated during the kneading process become a solidified product, the strength of the solidified product will decrease.

(3) During solidification, when waste and plastic are separated due to the difference in specific gravity and made into a solidified product, homogeneity, strength, etc. may not be obtained.

The present invention is intended to eliminate the drawbacks of the prior art, and its purpose is to provide simple equipment, low radioactivity leaching rate to water, excellent homogeneity and strength, and safe handling. Another object of the present invention is to provide a method for solidifying radioactive waste that can be processed into a highly solidified material, and another object is to provide a solidifying device for radioactive waste that can appropriately implement the method.

The method according to the present invention dehydrates radioactive waste liquid containing solid content, stirs the solid content obtained by dehydration, heats it, and dries it, then adds a binder, heats it, and 100 mm (100 mm of water column) of the solid content. ) The above-mentioned solid content is kneaded with a solidifying agent under a strong negative pressure state and stirred at high speed while preventing the generation of bubbles to granulate and solidify the solid content.

Furthermore, the apparatus according to the present invention created to carry out the above method includes a dehydrator for radioactive waste liquid containing solid content, a jacket that can selectively use a heating medium and a refrigerant, and a stirring blade. and a mixer for kneading the solid content obtained in the dehydrator and a solidifying agent, a pressure reduction line for reducing the pressure inside the mixer to a strong negative pressure of 100 mm (water column) or more, and a heat medium in the jacket of the mixer. A heating line and a cooling line for a refrigerant, and a solidifying agent supply line for supplying a solidifying agent into the mixer, and the mixer has a means for adding a binder, and the solid content is added with a binder. It is characterized by having a structure in which radioactive waste to which is added and kneaded a solidifying agent can be stirred at a high enough speed to form granules.

Hereinafter, the apparatus of the present invention and the method of the present invention implemented using the same will be explained based on the drawings.

FIG. 1 shows a first embodiment of an apparatus for carrying out the method of the invention.

This embodiment includes a storage tank 1 for radioactive waste liquid, a centrifugal dehydrator 2 for the radioactive waste liquid, a measuring hopper 3 for dehydrated solids, a stirring blade 5 rotated by a motor M, and a jacket for a heat medium (not shown). omission)
and a thermometer 6, a heating line 7 for heating medium, a pressure reduction line 8 for reducing the pressure inside the fluidization mixer 4, a solidifying agent tank 10 and its feeder 1.
1 and a drum can 12 for storing the solidified material, and shows a case suitable for solidifying radioactive waste using a thermoplastic resin as the solidifying agent.

The heating line 7 is connected to a heat source such as a boiler, and the pressure reduction line 8 is connected to a pressure reduction device (not shown) equipped with an ejector having a capacity of 200 mm (water column). is omitted in the drawing.

The fluidizing mixer 4 has a stirring blade 5 rotationally driven by a motor M, a jacket for a heating medium (not shown), and a thermometer 6, and the fluidizing mixer 4 has a stirring blade 5 rotationally driven by a motor M, a jacket for a heating medium (not shown), and a thermometer 6. The pressure is reduced to -200 mm (water column) via a vacuum line 8. When carrying out the present invention, the above negative pressure is used to prevent foaming of the kneaded material.
It is necessary to create a negative pressure stronger than at least -100mm (water column).

Examples of the radioactive waste liquid include used powdered resin containing a large amount of solid content, granular resin, super-assistant,
A clad slurry or the like may be used, and a mixture thereof may also be used. Further, it is advisable to add a flocculant to the clad slurry if necessary. These radioactive wastes are stored in the storage tank 1.

Then, the radioactive waste to be treated is supplied from the storage tank 1 together with the transferred water to the centrifugal dehydrator 2, dehydrated by the centrifugal dehydrator 2, and its solid content is measured by the measuring hopper 3 and fluidized and mixed. Supply to machine 4.

Then, in the fluidization mixer 4, the solid content is basically heated under reduced pressure, stirred by the stirring blade 5, and dried. The dry state of this solid content is
It is detected by a thermometer 6 and a pressure gauge 9.

After the solid content of the radioactive waste is dried, a solid solidification agent is added from the solidification agent tank 10 of the solidification agent line through the feeder 11, and then heated to melt the solidification agent and remove the dried radioactive waste. The solid content and the molten solidifying agent are kneaded and homogenized. Note that the solidifying agent may be melted in advance and the molten solidifying agent may be supplied into the fluidization mixer 4 through a pipe.

After the kneading is completed, the kneaded mixture of radioactive waste solid content and solidifying agent is transferred from the fluidization mixer 4 to the drum can 12.
Fill the container and leave it to cool to solidify.

As mentioned above, when the solid content of the radioactive waste and the solidifying agent are mixed together, the solid content and the solidifying agent are mixed under a reduced pressure of -200 mm (water column), so the solid content and the solidifying agent waste are put into the drum can 12. Under normal pressure, the generation of bubbles due to air is suppressed, and the solidified product has a low radioactivity leaching rate with respect to water, and has excellent homogeneity and strength.

Therefore, by reducing the pressure as much as possible during drying of the solid content of radioactive waste and before supplying and mixing the solidifying agent, the strength of the solidified material is increased, and it is also preferable in terms of the amount of steam used. .

Next, FIG. 2 shows a second embodiment of an apparatus for carrying out the method of the present invention.

What is shown in FIG. 2 is a fluidizing mixer 4 having a jacket (not shown) that can selectively use a heating medium and a refrigerant, a set of a heating medium line 7 for a heating medium and a cooling line 13 for a refrigerant; This example is equipped with a solidifying agent supply line having a polyester tank 14 and a polymerization catalyst tank 15, and is suitable for solidifying radioactive waste using a thermosetting resin as the solidifying agent.

The cooling line 13 is connected to a refrigerator (not shown), and the combination of the heating line 7 and the cooling line 13 is configured to be selectively activated by switching a valve.

The heating medium in the jacket of the fluidizing mixer 4 is heated by the heating line 7, the refrigerant is cooled by the cooling line 13, and the fluidizing mixer 4 is heated through the heating medium and cooled through the refrigerant. It is becoming more and more like this.

Then, the solid content of the dehydrated radioactive waste is supplied to the fluidization mixer 4, and at the initial stage of treatment, the fluidization mixer 4 is heated through the heating line 7 and the heating medium to remove the solid content of the radioactive waste. In principle, it is heated and dried in a fluidized mixer 4 under reduced pressure.

After the solid content of radioactive waste is dried, cooling line 1
The fluidizing mixer 4 is cooled through the cooling line 13 and the refrigerant, and the temperature is adjusted so that the thermosetting resin supplied as a solidifying agent does not harden during kneading.

After the solid content of the radioactive waste has been cooled, the unsaturated polyester stored in the polyester tank 14 of the solidification agent supply line and the polymerization catalyst stored in the polymerization catalyst tank 15 are mixed into the fluidization mixer 4. The dried solid content, unsaturated polyester, and polymerization catalyst are kneaded under reduced pressure. Note that, if necessary, a temperature-sensitive polymerization inhibitor may be added to the unsaturated polyester in advance and stored in the polyester tank 14.

After the solid content of the radioactive waste, the unsaturated polyester as a thermosetting resin, and the polymerization catalyst have been kneaded, the drum can is filled into the drum 12, and the kneaded material in the drum 12 is once brought to a predetermined temperature. Once this is reached, polymerization will begin and solidify.

In this case as well, the generation of air bubbles can be suppressed by reducing the pressure as much as possible before supplying and mixing the solidifying agent.

The other configurations of the apparatus shown in FIG. 2 and the implementation steps of the method are the same as those described for the apparatus shown in FIG.

Furthermore, FIG. 3 shows a third embodiment of an apparatus for carrying out the method of the invention.

This example is a motor with variable rotation speed.
A fluidizing mixer 4 having a stirring blade 5 connected to M', a set of heating line 7 and cooling line 13, a set of solidifying agent tank 10 and feeder 11, and a set of polyester tank 14 and polymerization catalyst tank 15. and a solidifying agent supply line.

In principle, the solid content of the radioactive waste is heated and dried in a reduced pressure state in the fluidization mixer 4, and after drying is completed, the fluidization mixer 4 is preferably heated.
Bring the inside to normal pressure. In other words, it is optional whether the solid content is dried at normal pressure or reduced pressure, but even when drying at normal pressure, the system of the fluidization mixer 4 is kept under a weak negative pressure to prevent radiation scattering. It is necessary to keep it.

Next, a solidifying agent as a binder is added into the fluidizing mixer 4 through the solidifying agent tank 10 and feeder 11 of the solidifying agent supply line, and heated to soften and melt the solidifying agent.

In this embodiment, a thermoplastic resin is used as the solidifying agent, which is the binder, and the amount thereof is smaller than that in the first embodiment. Further, the operating conditions are such that the rotation speed of the stirring blade 5 of the fluidization mixer 4 is high and the heating temperature is somewhat low.

By stirring the solid content of radioactive waste and the solidifying agent under the above operating conditions, the solid content is granulated into granules.

The degree of granulation can be detected by the electric power of the motor M' for rotating the stirring blade 5.

After the completion of the granulation, the rotational speed of the stirring blade 5 is lowered, heating is stopped, and the temperature is lowered to below the softening point of the solidifying agent.
Alternatively, after reducing the pressure and cooling the inside of the fluidization mixer 4, as in the case of the second embodiment, unsaturated polyester is supplied from the polyester tank 14 of the solidifying agent supply line for polymerization. A polymerization catalyst may be supplied from the catalyst tank 15, and after kneading the granular solid content, unsaturated polyester that is a thermosetting resin, and the polymerization catalyst, the mixture may be filled into the drum can 12 and solidified. .

According to this third embodiment, handling safety is further improved by granulating and solidifying the solid content of radioactive waste.

The other configuration of the apparatus shown in FIG. 3 and the implementation process of the method using this apparatus are the same as described for the apparatus shown in FIG. 1.

Moving forward, FIG. 4 shows a fourth embodiment for carrying out the method of the invention.

This embodiment includes a solidifying agent supply line having a set of a polyester tank 14, a polymerization catalyst tank 15, and a water-soluble binder tank 16.

After the solid content of the radioactive waste is dried in the fluidization mixer 4, a binder is supplied from the binder tank 16 of the solidifying agent supply line, and the solid content and binder are heated and stirred to form granules. do.

The binder includes polyvinyl alcohol,
Water-soluble materials such as carboxymethyl cellulose and water glass are generally used.

After the solid content of the radioactive waste is granulated, the granular solid content may be treated in the same manner as in the embodiment shown in FIG. Even if it is transported to a field and stored, it is safe because it is in granular form and there is no inconvenience of scattering.

The other configurations of the apparatus shown in this fourth embodiment and the steps of the method of the present invention carried out using this apparatus are the same as in the first embodiment.

As detailed above, according to the method of the present invention,
With simple equipment, it can be processed into granules that have a low radioactive leaching rate with respect to water, are excellent in homogeneity and strength, are easy to handle, and are highly safe.

[Brief explanation of the drawing]

1, 2, 3 and 4 respectively show the first, second and third parts of the apparatus for carrying out the method of the present invention.
and FIG. 7 is a system diagram showing a fourth example. 1... Radioactive waste storage tank, 2... Centrifugal dehydrator, 3... Solid content measuring hopper, 4... Fluidization mixer, 5... Stirring blade, M, M'... Stirring blade Motor, 7... Heating line, 8... Decompression line, 10... Solidifying agent tank, 11... Solidifying agent feeder, 12... Drum can for storing solidified material, 1
3...Cooling line, 14...Polyester tank, 15...Polymerization catalyst tank, 16...Binder tank.

Claims (1)

[Scope of Claims] 1. After dehydrating the radioactive waste liquid containing solid content, stirring, heating and drying the solid content obtained by dehydration, a binder is added and the pressure is reduced to an extent that can prevent the generation of bubbles. 1. A method for solidifying radioactive waste, comprising granulating the solid content by stirring at high speed in a state where the solid content is granulated. 2. The method for solidifying radioactive waste according to claim 1, characterized in that the solidifying agent is a thermoplastic resin. 3. The method for solidifying radioactive waste according to claim 1, characterized in that the solidifying agent is a thermosetting resin. 4. The method for solidifying radioactive waste according to claim 1, wherein the binder is a thermoplastic resin. 5. The method for solidifying radioactive waste according to claim 1, characterized in that the binder is water-soluble. 6. Mixing that includes a dehydrator for radioactive waste liquid containing solid content, a jacket that can selectively use a heating medium and a refrigerant, and a stirring blade, and kneads the solid content obtained in the dehydrator with a solidifying agent. a decompression line for reducing the pressure inside the mixer to a negative pressure that can prevent the generation of bubbles; a heating line for a heat medium and a cooling line for a refrigerant in the jacket of the mixer; and a solidifying agent in the mixer. and a solidifying agent supply line, and the mixer has means for adding a binder, and the radioactive waste with the binder added to the solid content and kneaded with the solidifying agent is granulated. A radioactive waste solidification processing apparatus characterized by having a structure capable of stirring at a high speed sufficient to cause granulation.