JPS6140959B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for disposing of radioactive waste, and in particular, the present invention relates to a method for disposing of radioactive waste, and in particular, the present invention relates to a method for disposing of radioactive waste, and in particular, used granular or powdery ion exchange resins and filters generated from nuclear power facilities such as nuclear power plants. Concerning methods for processing radioactive waste such as auxiliary agents and recycled waste liquid.

[Background of the invention]

In nuclear power facilities such as nuclear power plants, radioactive sludge is produced by granular ion exchange resin used for reactor water purification, filter aids containing cellulose as a main component (KC floc and Solka floc), and granular ion exchange resin. occurs. These are long half-life nuclides such as ⁶⁰ Co and ¹³⁷ Cs.
Because it contains radioactivity, it takes a long time for its radioactivity to decay. For this reason, conventionally, these radioactive sludges are dehydrated to about 50% by weight using a centrifugal dehydrator, etc.
After being mixed and solidified with cement, asphalt, etc. in drums, it is stored and stored within the facility. However, as the number of years of operation of nuclear power plants increases, the amount of radioactive waste stored is increasing, and securing storage space has become a problem.For this reason, final disposal methods such as offshore speculation are being considered. .

In order to use solidified radioactive waste in the ocean, the solidified material must satisfy conditions such as strength and radioactivity elution rate, and its density must be sufficiently greater than that of seawater. Currently, the average density of solidified material is 1.2g/
cm ³ or more is considered necessary.

Solidified asphalt and solidified plastic are
Compared to solidified cement, it has the advantage of having a lower radioactivity elution rate, but because its density is as low as approximately 1.0 g/cm ³ , when radioactive waste with low density such as radioactive sludge is solidified, the solidified material There may be cases where it is not possible to ensure an average density of 1.2 g/cm ³ or more.

For this reason, it has been considered to mix solid waste with a high density into the sludge when solidifying and storing radioactive sludge and the like. That is, as shown in Fig. 1, the sludge 2 made of ion exchange resin, filter auxiliary agent, etc. is dehydrated, and then recycled waste liquid containing sodium sulfate produced by regeneration of the ion exchange resin is passed through a centrifugal membrane desiccant machine. The powder obtained by evaporation drying is mixed with granulated pellets 3, and the mixture is filled into an internal container 6 in a drum 5. after that,
Asphalt 1 is filled into the drum 5 and solidified.

Even when conducting marine speculation, it is clear that it is desirable to minimize the number of solidified bodies to be speculated on. However, in the case of the conventional example, since the sludge 2 is only subjected to dehydration treatment, there is a drawback that the volume reduction ratio is small.

Furthermore, when the sludge 2 and pellets 3 are mixed and filled into the internal container 6 of the drum 5, and then a solidifying agent such as asphalt or plastic is injected into the drum 5, there are the following drawbacks. That is, since the sludge 2 has a minute particle size, the gap formed between the sludge 2 and the pellets 3 is extremely small, and the flow resistance when the solidifying agent passes through this gap is extremely large. I end up. For this reason, not only does it take a considerable amount of time to inject the solidifying agent, but also the type of solidifying agent that can be injected is limited to special types.

Furthermore, Japanese Patent Application Laid-Open No. 52-154999 discloses a technique in which radioactive solid content granulated after drying and dried radioactive waste resin are mixed and introduced into a container. The density of resin is approximately 0.8
g/cm ³ and the density of the solidifying agent is over 1.0 g/cm ³ , so when the solidifying agent is filled into a container and solidified, the waste resin floats to the surface and the waste resin is deposited on the top surface of the solidified body. The resin will be exposed. This makes it difficult to produce a homogeneous solidified body.

[Purpose of the invention]

An object of the present invention is to provide a radioactive waste treatment that can increase the amount of granular waste that can be filled into a storage container and prevent the waste from floating to the surface during filling with a solidifying agent to obtain a homogeneous solidified waste. We are here to provide you with a method.

[Summary of the invention]

The characteristics of the present invention are that radioactive waste powder is compressed and granulated to produce large particle size pellets with a density of 1.2 g/cm ³ or more, and radioactive waste powder is compressed and granulated to produce pellets with a density of 1.2 g/cm 3 or more.
Pellets with a small particle size of 1.2Kg/cm ³ or more are produced, the large particle size pellets and the small particle size pellets are filled into a container, and then a solidifying agent is filled into the container to dispose of the waste. The point is to produce a solidified body.

[Embodiments of the invention]

A preferred embodiment of the present invention will be described in detail below. Used granular ion exchange resin containing radioactive materials, granular ion exchange resin (a type of filter aid)
Alternatively, a radioactive sludge such as a filter aid containing cellulose as a main component is dehydrated and dried using a centrifugal thin film dryer and powdered. This is compressed under high pressure by a granulator to form pellets.
In addition to this radioactive sludge, another type of waste generated in large quantities at nuclear power plants is recycled waste liquid generated from ion exchange resin recycling operations. Usually, recycled waste liquid has sodium sulfate (Na ₂ SO ₄ ) as its main component. By treating this recycled waste liquid with a centrifugal thin film dryer, sodium sulfate powder can be obtained. This powder is also compressed under high pressure by a granulator to form pellets. These two
Seed pellets are mixed in the proportions described below, solidified using a solidifying material such as asphalt, and stored. In this way, a solidified body of radioactive waste is obtained.

Figure 2 schematically shows a cross section of the solidified radioactive waste obtained in this example, and shows that large particle size pellets 8 and small particle size pellets 4 are separated from each other by falling off. The mixture is mixed and filled into an inner container 6 made of a solid wire mesh, and this is fixed in a drum 5 with asphalt 1 to form a solidified body 7.

Experiments have revealed that it is easy to obtain a true density of about 1.2 g/cm ³ or more when sludge is made into pellets. In addition, the true density of sodium sulfate pellets is approximately 2.3 g/ ^cm3 , and the porosity when filled with almond-shaped pellets with a major axis of approximately 3 cm, a minor axis of approximately 2 cm, and a thickness of approximately 1 cm is approximately 50.
It was %. In addition, when the sludge pellets were shaped similarly to the sodium sulfate pellets, a porosity of 40 to 60 was obtained.

FIG. 3 shows the relationship between the particle size ratio and the minimum porosity when two types of particles having different average particle sizes are filled.
E has a porosity of 40 when filled with one type of pellet.
%, and F is when the porosity is 60%. As the ratio of the particle size of the small pellets 4 (small particle size) to the particle size of the large pellets 3 (large particle size) becomes smaller, the porosity decreases. In addition, the results of determining the average density of the solidified material at this time are shown in the fourth column.
As shown in the figure. However, the drum 5 is made of 200 mm, and the asphalt 1 with a thickness of 5 cm is provided near the outer wall of the drum 5. Therefore, the ratio of the volume of the inner container 6 to the volume of the drum 5 is 60%.
becomes. In addition, the true density of the sludge pellets is
1.2g/cm ³ , and the true density of sodium sulfate is 2.3g/cm ³ . In the figure, A ₁ and B ₁ are cases where the porosity is 40% when one type of pellet is filled alone,
Similarly, A ₂ and B ₂ are cases where the porosity is 60%. In addition, A ₁ and A ₂ are the cases where all the sludge pellets are _of large particle size and all _of the sodium sulfate pellets are of small particle size. This is the case when all of the sodium sulfate pellets are of large particle size. In addition, in order to obtain the minimum porosity shown in Fig. 4, the weight ratio Z (%) of large particle size
must be the proportion given by the following formula:

Here, ε is the porosity (%) when pellets are packed alone, ρ ₁ is the true density (g/cm 3 ) of large pellets, and ρ ₂ is the true density (g/cm ³ ) of small pellets. True density (g/cm ³ ). FIG. 5 shows the average density when pellets are packed at the weight ratio expressed by formula (1) above.

If a large amount of radioactive sludge is generated compared to the recycled waste liquid, it is necessary to store the sludge pellets as large particles.In this case, the particle size of the sodium sulfate pellets should be 1/10 or less of the large particle size. By doing so, the average density of the solidified material is 1.2 or more,
In addition, it becomes possible to achieve the closest packing, making it possible to significantly reduce the volume of radioactive waste.

In the above case, the volume reduction ratio of radioactive sludge is as follows. When the sludge is dehydrated to approximately 50% by weight, the bulk density of the sludge alone is
It is 0.1 to 0.4 g/cm ³ , and when made into pellets, a bulk density of 0.6 g/cm ³ or more is obtained, and the volume reduction ratio is about 1.5 to 6. This means that approximately 500 drums of radioactive sludge are expected to be generated per year in a 100 MWe power plant, so the volume will be reduced by approximately 150 drums per year.

Granular ion exchange resin, granular ion exchange resin (filter auxiliary agent), filter auxiliary agent mainly composed of cellulose, and recycled waste liquid are separately pulverized in a centrifugal thin film dryer to make pellets of a single composition. By filling a predetermined amount of pellets into the drum 5, the average density of the solidified material can be adjusted.

According to this example, by compressing the radioactive sludge into pellets and filling it, it is possible to reduce the volume, and by changing the particle size of the mixed sodium sulfate pellets, close packing can be achieved. The amount of radioactive waste to be filled will increase by approximately 1.5 times. Furthermore, it is possible to increase the average density of the solidified material to 1.2 g/cm ³ or more, which satisfies the standard value for marine speculation.

Furthermore, according to this embodiment, the radioactive waste is made into large particle size pellets and small particle size pellets and is filled into the storage container, so the gaps between the pellets are considerably larger than in the conventional case. Therefore, it becomes extremely easy to inject the solidifying agent between the waste materials (pellets).

〔Effect of the invention〕

As described above, in the method of the present invention, radioactive waste is produced into large particle size pellets and small particle size pellets with a density of 1.2 g/cm ³ or more, and these are filled into a storage container. Therefore, the amount of granular waste that can be filled into the container can be increased, and since both large and small pellets have a density of 1.2 g/cm ³ or more, the waste does not float to the surface when filling with the solidifying agent, and therefore the pellets are homogeneous. This has the effect of making it possible to obtain solidified waste.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a solidified body obtained by a conventional radioactive waste processing method, and FIG. 2 is a vertical cross-sectional view of a solidified body obtained by a preferred embodiment of the present invention. Figure 3 is a characteristic diagram showing the change in minimum porosity when the ratio of the average particle diameters of two types of pellets is changed, and Figure 4 is a characteristic diagram showing the change in minimum porosity when the ratio of the average particle sizes of two types of pellets is changed. FIG. 3 is a characteristic diagram showing changes in the average density of a solidified body in the case of FIG. 1... Asphalt, 4, 8... Pellet, 5
...Drum, 6...Inner container.

Claims (1)

[Claims] 1 Compression granulation of radioactive waste powder to reduce density
Pellets with a large particle size of 1.2 g/cm ³ or more and pellets with a small particle size with a density of 1.2 g/cm ³ or more are produced by compressing and granulating radioactive waste powder, and the pellets with the large particle size are and pellets of small particle size into a container, and then a solidifying agent is filled into the container to produce a solidified waste material.