JPH0450558B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for solidifying radioactive waste, and more particularly to a method for melting and solidifying incinerated ash of radioactive waste.

Conventionally, combustible waste contaminated with radioactivity generated from facilities handling radioactive materials such as nuclear power plants is generally incinerated, and the incinerated ash is filled into drum cans, etc., and transported to the facility. It is usually stored in an appropriate location inside the building. However, since these incinerated ash are in the form of powder, it is desirable to stabilize and reduce the volume of the incinerated ash before transporting or storing the drum can filled with incinerated ash, and various methods for this treatment have been studied. For example, a method of solidifying incineration ash with cement has been proposed. However, the method of solidifying this incineration ash with cement is as follows: (1) In order to mix ash and cement to obtain a solidified material with stable density and strength, the weight ratio of ash and cement must be 1 part ash to 4 parts cement. Therefore, the volume of the solidified material becomes larger than the volume of the ash, resulting in an increase in volume.

(2) When mixing ash and cement, metal contaminants in the incinerated ash react with the alkaline aqueous solution of cement to generate hydrogen gas, which creates voids in the solidified material and reduces density, strength, etc. There is a lack of stability.

There were other drawbacks.

The present invention solves the above conventional drawbacks by converting radioactive waste incineration ash into an inorganic solidified body that can be safely stored and transported, and at the same time reducing the volume of the obtained solidified body from the original volume of the incinerated ash. , which attempts to provide a method for melting and solidifying radioactive waste incineration ash that requires less storage space. A metal container is installed in a cylindrical heating body made of aluminum, and a flux that forms a eutectic with radioactive waste incineration ash is supplied into the container, and is melted into a liquid state in the container by the induction heating coil. At the same time, radioactive waste incineration ash is supplied onto the above-mentioned flux, and oxygen-containing gas is supplied above the liquid surface of the above-mentioned flux to burn unburned content in the above-mentioned incineration ash. A method for melting and solidifying radioactive waste incineration ash, characterized in that the incineration ash is dissolved in a solvent and then cooled, and the incineration ash is fixed in the container as a eutectic with the flux.

The present invention will be explained in more detail below with reference to the drawings.

Radioactive waste incineration ash 1 temporarily stored in a drum can etc. is stored in a closed hopper 2, and the components of the incineration ash 1, SiO ₂ ,
A fluxing agent 3 such as boric acid, borax, sodium carbonate, etc., which forms a eutectic with CaO, Fe ₂ O ₃ , MgO, AI ₂ O _{3 ,} etc., is stored in another hopper 4 . On the other hand, a metal container 8 is installed in a metal cylindrical heating body 7 provided in a closed container-shaped furnace body 6 of the induction heating furnace 5, and an induction heating coil 9 is provided on the outer periphery of the furnace body 6. The cylindrical heating body 7 is heated to about 400 to 1100°C. If the flux 3 in the hopper 4 is supplied into the container 8 through the supply port 12 by the flux supply machine 11, the cylindrical heating body 7
The flux melts in the container 8 and becomes liquid due to heat radiation and heat transfer from the container 8 and heating of the container 8 itself by the induction heating coil 9. For example, when boric acid is used as the fluxing agent 3, it melts at about 450°C, and when borax or a mixture of boric acid and sodium carbonate is used, it melts at about 800°C and becomes liquid. In this case, instead of using special fluxing agents such as borax, boric acid, and sodium carbonate, glass waste such as waste glass, cullet, and used HEPA filter media is used, and the boron, sodium, etc. in these glasses are used. can also be used as a flux.

Next, the incinerated ash 1 is supplied little by little onto the melted flux in the container 8 by the incinerated ash feeder 13, and the incinerated ash 1 is supplied in small quantities to burn off the unburned matter such as carbon contained in the incinerated ash 1. Combustion air (preferably containing the minimum necessary amount of oxygen) 14 is supplied onto the flux surface through the introduction pipe 15, and the unburned content in the combustion ash 1 is combusted by this combustion air, make up ash
SiO ₂ and other components are dissolved as a eutectic with a flux. In addition, for the purpose of shortening the time required for the incinerated ash to dissolve into the flux, an appropriate amount of the flux 3 can be supplied into the container 8 at the same time as the incinerated ash 1. In addition to SiO ₂ and other components mentioned above, the incineration ash 1 supplied into the container 8 contains non-combustible impurities such as metals, bricks, asbestos, glass, concrete, and ceramic filter elements. Although these may not form a eutectic, they are all incorporated into the eutectic. The above operation is continued until the container 8 is almost completely filled with the eutectic, and then the furnace body 6 and the container 8 are cooled by natural cooling or the like, and the eutectic is solidified and fixed in the container 8. The solidified eutectic is lowered together with the bottom lid 17 on which the container 8 is placed, and the entire container 8 is taken out.A new container 8 is placed on the bottom lid 17, and the same process is repeated.

During the above operation, in order to prevent radioactive contamination, the inside of the incinerated ash hopper 2, incinerated ash feeder 13, induction heating furnace 5, etc. are all connected to the duct 2 by the blower 20.
The air is suctioned and exhausted through the filter 1, and is cleaned by the filter 22.

In addition, when feeding the incinerated ash 1 onto the melted flux 3 in the above process, if a large amount of incinerated ash is fed at once, the unburned substances in the incinerated ash will not be completely combusted and will float on the liquid surface and cause other co-occurrence. Since it interferes with the formation of melt, it is preferable to add incineration ash little by little to the extent that unburned matter is completely combusted. Furthermore, if a large amount of oxygen necessary to burn the unburned content in the incineration ash is supplied into the furnace body 6, the cylindrical heating element 7 or the metal container 8 will be subject to high-temperature oxidation, resulting in significant deterioration. The amount of oxygen supplied is the minimum amount necessary for the unburned matter to burn, and an inert gas 18 is provided in the furnace body 6.
It is preferable to supply the following. Also,
In this case, the state of combustion of unburned matter or the state of melting of ash can be detected using a detector 19 such as a monitor TV or thermometer.
It is necessary to detect the

Next, examples of the present invention will be given.

Example Non-radioactive simulated incineration ash (apparent density: 0.4 to 0.5 g/cm ³ ) having almost the same composition as radioactive waste was prepared in advance and heated in a high-frequency induction heating furnace with an output of 100 KW.
Installed inside an induction heating cylinder heated to 1100℃
Melt borax as a flux in a stainless steel container of 350 mmφ x 500 mmH, and feed the simulated incineration ash onto the melt surface at a feeding rate of about 6 to 12 kg/H,
At the same time, in order to burn the unburned content in the incineration ash, air of 5 to 30 Nm ³ /H was supplied to burn the unburned content, and all the ash was dissolved in the flux. After incineration ash was supplied in an amount almost equal to the weight of the flux, it was cooled and solidified, and solidified in the container as a eutectic product with the flux. The density of the obtained solidified material is approximately 2.4 to 2.6 g/cm ³ ,
The compressive strength was about 1000-2000 Kg/ ^cm2 . Also,
The leaching rate of C _S from the solidified material is approximately 10 ^-5 to 10 ^-7 g/cm ² .
It was d.

As shown in the above description and examples, the method of the present invention provides the following effects.

(1) Powdered radioactive waste incineration ash can be contained in a container as a stable inorganic solid.

(2) Even if the incineration ash contains a large amount of unburned matter, a stable solidified material can be obtained because the oxygen-containing gas is supplied above the flux surface to combust the unburned matter.

(3) Even if the incineration ash contains non-combustible impurities such as metals and bricks, these impurities can be incorporated into the eutectic mixture of the flux and the incineration ash and solidified.

(4) The volume of the solidified material obtained is 1/3 of the volume of incinerated ash.
It is approximately 1/5th of the original size, allowing for a large volume reduction.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing a specific example of the apparatus used in the method of the present invention. 1...Radioactive waste incineration ash, 3...Fluxing agent, 5...
... induction heating furnace, 6 ... furnace body, 7 ... cylindrical heating body,
8... Container, 9... Induction heating coil, 14... Combustion air.

Claims (1)

[Claims] 1. A metal container is installed in a metal cylindrical heating body provided in a furnace equipped with an induction heating coil, and a flux that forms a eutectic with radioactive waste incineration ash is placed in the metal container. Radioactive waste incineration ash is supplied onto the flux which is supplied into the vessel and melted into liquid form within the vessel by the induction heating coil, and an oxygen-containing gas is supplied onto the liquid surface of the flux. to burn the unburned content in the incinerated ash, dissolve the incinerated ash in the flux, cool it, and fix the incinerated ash in the container as a eutectic with the flux. A method for melting and solidifying radioactive waste incineration ash, characterized by: 2. The method for melting and solidifying radioactive waste incineration ash according to claim 1, wherein the fluxing agent is at least one of boric acid, borax, and sodium carbonate.