JPS6246840B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for disposing of radioactive waste, and in particular, it is an object of the present invention to provide a method for purposefully reducing the volume of radioactive waste generated in pressurized water nuclear power plants.

Nuclear power plants with pressurized water reactors generate various types of radioactive waste. Most of this is waste water from the primary cooling system or secondary cooling system, waste water from equipment, waste water used for washing work clothes, flammable miscellaneous solids such as paper, cloth, polyethylene, etc. occupied by. Due to their nature, these radioactive wastes must be managed and stored with great care, and their volume must be reduced for convenience of handling and other reasons.

Typical conventional treatment and storage methods for these radioactive wastes are as follows.

First, let's talk about the waste liquid mentioned above. Boron, which is a moderator, is dissolved in the waste liquid as boric acid, and this waste liquid is subjected to evaporation treatment to concentrate the boric acid concentration to about 12% by weight and reduce the volume. Further, the waste liquid is subjected to reverse osmosis membrane treatment to concentrate the detergent concentration to about 5% by weight and reduce the volume. Thereafter, these concentrated waste liquids are mixed with cement, asphalt, etc., solidified in drums, and managed and stored on the premises of the power plant or in a designated storage area.

However, this method had the following drawbacks. Nuclear power plants continue to operate for a considerable period of time, and solidified radioactive waste liquid also needs to be managed and stored for a considerable period of time. For this reason, as nuclear power plants continue to operate, the cumulative amount of radioactive waste fluid that must be treated and stored continues to increase, but conventional concentration is insufficient to reduce the volume, and cement solidified bodies, etc. Since the addition of 2000 yen is accompanied by a considerable increase in volume, storage areas must be prepared one after another to accommodate it. Furthermore, once it is mixed with cement or the like and solidified, the only way to dispose of it is to dispose of it, and it is not possible to adopt an appropriate next disposal method in response to the increase in the amount of storage. Therefore, there is a need for a processing method for storing and managing the concentrated waste liquid as a solidified product whose volume is further reduced.

Generally speaking, as a method for reducing the volume of waste liquid, fluidized bed
Baking methods such as baking method and spray baking method are conventionally known. Both the fluidized bed sintering method and the spray sintering method
The fired product can be obtained as a powder or granule, but since it has drawbacks such as difficulty in handling, problems with scattering, and low apparent density, it is considered to further reduce the volume into pellets. It is being

On the other hand, the volume of the combustible miscellaneous solids mentioned above is reduced by incineration, and the remaining incineration ash is directly packed in drums and stored under management within the premises of the power plant, etc., as described above. However, this method had the following drawbacks. Because the apparent density of incinerated ash is small, the cumulative amount of radioactive incinerated ash that must be managed and stored will continue to increase as nuclear power plants continue to operate, as mentioned above, but volume reduction is still not possible. It is enough. In addition, since the incineration ash is obtained as a powder, there are problems such as difficulty in handling and scattering.

As a result of intensive research to provide a treatment method that does not have the drawbacks of conventional methods, the present inventors found that the calcination product of concentrated waste liquid generated in pressurized water nuclear power plants itself has excellent properties as a binder. The present invention was completed based on this knowledge. That is, the present invention solidifies pellets by blending 50% by weight or more of the incineration product of concentrated waste liquid generated at pressurized water nuclear power plants with the incineration ash of combustible miscellaneous solids generated at pressurized water nuclear power plants. This article focuses on a method for disposing of radioactive waste that is characterized by the following.

Hereinafter, specific examples will be explained in detail.

To simulate the concentrated waste liquid mentioned above, sodium hydroxide and sodium carbonate were added to a 12% by weight aqueous solution of boric acid to adjust the pH to about 7 from the viewpoint of corrosion prevention (hereinafter referred to as boric acid waste liquid).
A 5% by weight aqueous detergent solution (hereinafter referred to as detergent waste liquid) was used as the concentrated waste liquid. Each of these or a mixture of these is used in a fluidized bed kiln.
It was made into a baked product.

As a simulator of the above-mentioned combustible miscellaneous solids,
A mixture of paper, cloth, and polyethylene in equal amounts by weight was used, and the incineration residue was obtained using a fluidized bed incinerator.

These were used alone as a comparative example or mixed as an example to form pellets by tabletting. The shape of the pellet is about 20×8.

Properties of calcined product obtained from concentrated waste liquid The calcined product does not require the addition of a binder and can be molded into perfect pellets without cracking or peeling on its own. The compressive strength and density of the prepared pellets are shown in FIGS. 1 and 2, respectively.

From these figures, the tableting pressure is 4.5 tons (1.4 tons/
cm ² ) or more, it satisfies the current provisional ocean dumping guidelines of compressive strength of 150 kg/cm ² or more and density of 1.2 g/cm ³ or more, and does not require treatment such as re-grinding.
In this form, it can be solidified with polymers and dumped into the ocean. Even if they are not dumped into the ocean, they are easy to handle because of their strong properties.

Properties of incinerated ash obtained from combustible miscellaneous solids On the other hand, incinerated ash could not be molded at all by itself. Therefore, an attempt was made to create pellets by adding a cellulose-based binder. FIG. 3 shows the condition of the pellets depending on the amount of binder added.

In this figure, the areas show areas where pellets cannot be formed at all and remain in a disjointed state, and areas where pellets can be formed but have cracks.
The area shows the area where only pellets that are easily peeled or cracked can be formed, and the area shows the area where perfect pellets without cracking or peeling can be formed. As is clear from this figure, complete pellets can be formed by adding more than 30% binder.
However, the addition of such a large amount of binder has the effect of offsetting volume reduction, which is one of the main purposes of pellet molding, and is not desirable from this point of view.

Therefore, we focused on the fact that the sintered product can be molded into perfect pellets without cracks on its own, and created pellets by adding it to the incinerated ash. The condition, compressive strength, and density of the pellets thus prepared are shown in FIGS. 4 to 6, respectively.

As is clear from FIG. 4, if pellets are formed by adding 50% by weight or more of the sintered product to the incinerated ash, perfect pellets without cracking or peeling can be obtained. In FIG. 4, , and regions indicate the same regions as described with respect to FIG.

From FIG. 5: Comparing to the pellets of the sintered product alone, the compressed density increases when it is added to the incinerated ash. In the figure, α is 4.5 tons of tableting pressure, and β
indicates the case of 2 tons tableting pressure.

In this way, the pellets formed by mixing the sintered product with the incinerated ash exhibit better properties by exhibiting their mutual features. In addition, from the perspective of the amount of waste generated in the entire nuclear power plant, since there is no addition of binder that would cause an increase in the amount, the volume can be reduced by the amount that is solidified from powder to pellets. Incidentally, the bulk density of the granular material of the sintered product and the incinerated ash is 0.4 to 0.8 g/cm ³ .

From FIG. 6, it can be seen that the density of the pellet increases as the amount of the calcination product added increases. In the figure, the α band shows the case of 4.5 ton tableting pressure, and the β band shows the case of 2 ton tableting pressure.

Based on these facts, in order to obtain good incineration ash pellets, as shown in Figures 4 to 6, incineration products should be mixed into the incineration ash at a ratio of 50% by weight or more, preferably close to 50% by weight. It is clear that it is possible to mold pellets with sufficient compressive strength.

[Brief explanation of the drawing]

Figure 1 shows the relationship between tableting pressure (tons) and compressive strength (Kg/cm ² ) of the calcined product obtained from concentrated waste liquid.
The figure shows the tableting pressure (tons) and density (g/
Figure ³ is a graph showing the relationship between tableting pressure (tons) when binders are added in various proportions to incineration ash obtained from combustible miscellaneous solids. Figures 4 to 6 are graphs showing the effects of the present invention.
A graph showing the state when calcination products obtained from concentrated waste liquid in various proportions are added as a function of tableting pressure (tons). The compressive strength of the compressed product (Kg/
Fig. ⁶ is a graph showing the density (g/cm ³ ) of the compressed product at the same tableting pressure based on the same standard.

Claims (1)

[Claims] 1. The incineration ash of flammable miscellaneous solids generated at pressurized water nuclear power plants is blended with 50% by weight or more of the incineration product of concentrated waste liquid generated at the same power plants, and solidified into pellets. Radioactive waste disposal method.