JPS633280B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to a solidification treatment method for high-level radioactive waste generated during the reprocessing of spent nuclear fuel, and a solidification treatment container used therein.

The waste emitted from spent nuclear fuel reprocessing plants is fission products (hereinafter simply referred to as FP).
It is called high-level radioactive waste because it contains actinides and extremely high radioactivity ( ¹⁰³ curies per effluent), and in order to completely isolate it from the living environment of living things, it is calcined. Various treatment methods have been proposed, such as solidification, vitrification, metal solidification, and ceramic solidification.

Among them, the ceramic solidification method, which uses a hot press to sinter and solidify, can reduce the volume of radioactive waste liquid as much as possible, and furthermore, it is possible to solidify it at a relatively low temperature, so it is possible to It is attracting attention as a promising solidification treatment method because it can prevent the volatilization of volatile components such as 137 and ruthenium-106 as much as possible.

The purpose of this invention is to be able to reduce the volume of high-level radioactive waste by preventing the volatilization of the volatile components as much as possible when solidifying high-level radioactive waste. It is an object of the present invention to provide a solidification treatment method that can simultaneously carry out encapsulation and encapsulation, and an optimal treatment container for use in carrying out this method.

Although this invention was mainly developed for solidifying high-level radioactive waste,
Needless to say, this invention can be applied as is to other cases where low-level radioactive waste is solidified.

This invention will be explained in detail below based on the drawings. For example, high-level radioactive waste discharged from a spent nuclear fuel reprocessing plant is stored in a tank for several years and then This is evaporated and concentrated, and then calcined in a sintering means such as a rotary kiln to form a granular material.The granular material and a solidification treatment agent such as a ceramic forming substance are blended in an appropriate ratio, and the mixture is heated from a hopper 1. It is accommodated in the press mold 2.

Next, this mixture 3 is cold pressed, and this mixed molded product 4 is placed in a processing container main body 5 having a cylindrical shape with an open top.
Contain it inside. Next, a cylindrical lid 6 with an open bottom is fitted into the processing container main body 5, and the container is housed in, for example, a vacuum hot press and heated for a predetermined period of time. Apply pressure. Then, the lid 6 that is fitted into the processing container body 5 is press-fitted while being strongly pressed against the inner wall of the processing container main body 5 by the mixed molded product 4 that is pushed into the interior, and finally the mixed molded product 4 is compressed from above and below and sintered in a state close to the theoretical density while reducing its volume to form a solidified ceramic body, and at the same time this sintered body is sealed in a processing container 7. .

Example: 30 parts by weight of high-level radioactive waste with a particle size of 200 mesh or less, which was calcined at 650°C for 2 hours using a rotary kiln, was mixed with 70 parts by weight of natural zeolite, which was heat-treated at 600°C for 1 hour. Fill the mixture into a press mold with an inner diameter of 50 mmφ and a depth of 100 m using a hopper, and press it at room temperature using a press.
After pressure molding at a pressure of 1 t/cm ² , the molded product was taken out and housed in a stainless steel can-shaped processing container body with an inner diameter of 51 mmφ and a depth of 50 mm. Next, the outer diameter is 51mm and the height is 50mm to this processing container body.
Cover with the same stainless steel can-shaped lid of mm.
This is combined with a tantalum heating element with a maximum operating temperature of 1250℃,
It was installed inside the core tube of a hot press with a maximum total pressure of 10 tons. After evacuating the inside, the temperature inside the furnace was raised to 950°C at a heating rate of 200°C/h and maintained at this heating temperature for 1 hour.
After pressurizing with a pressure of 150Kg/cm ² for 30 minutes,
It was allowed to cool naturally to room temperature and then taken out.

It was found that in the processing container obtained, the lid completely fitted into the main body of the processing container, and the two were in close contact with each other, so that the internal airtightness was completely maintained.

Next, the processing container was broken and the contents were taken out, and upon examination, it was found to be a dense solidified ceramic material with a density of 2808/cm ³ .

In other embodiments, the cold pressing may be performed within the processing vessel body 5 from the beginning. In this case, the radioactive waste and the solidification agent are further mixed in the processing container body 5 to form a sludge,
After drying this, it may be cold pressed.

Furthermore, in the case of hot pressing, on top of the ceramic solidified body that has been sintered by hot pressing,
Further, a method of continuous hot pressing by adding mixed powder and granular material and hot pressing may be used. In this case, the lid 3 is fitted during the final hot pressing.

Alternatively, if you want to complete sintering with one hot press and get the maximum effect,
It is preferable to use a method in which the mixed powder and granular material 3 is cold-pressed for the lid 6 as well, and then this is inserted into the solidification treatment container 5 and hot-pressed.

Note that the lid 6 does not necessarily have to be cylindrical as long as it is press-fitted into the processing container body 5; Since it can be crimped onto the inner wall of the processing container body 5, it is easy to seal the processing container main body 5.
It also has the advantage of increasing strength. Then, by removing the inner side of the lower edge of the cylindrical lid 6, it is made to have an acute angle.
The mixed powder and granular material 3 in the processing container main body 5 is easily press-fitted into the lid 6, and the force that tends to spread outside the lid 6 increases, further increasing the sealing effect.

Therefore, with this alone, the lid body 6 can be sufficiently press-fitted into the processing container body 5 and the interior can be sealed; however,
For safety, if the joint between the outer periphery of the lid 6 and the inner periphery of the processing container body 5 is welded, the adhesion between the two and the sealing of the sintered body will be more complete. be. The processing container body 5 and the lid 6 are made of a water-resistant and heat-resistant material such as stainless steel, and their wall thickness is thicker than that of a normal can body. Then, if necessary, the lid body 6,
It is preferable to provide through holes in other locations to serve as means for venting gas during sintering. In this case, it may be desirable to close the through hole later by means such as welding. Note that if the structure of the mixed powder and granular material can be made into a sufficiently dense state by cold pressing, the through holes are not necessarily necessary.

As a solidification treatment method for high-level radioactive waste,
The most technologically advanced vitrification method involves adding calcined bodies of high-level radioactive waste to raw materials with a glass composition ratio, heating and melting the mixture to about 1200℃, and vitrifying it, but the melting temperature is Glass is thermodynamically unstable and tends to partially crystallize, so there is a high risk of performance deterioration, and there are safety issues such as volatilization of cesium and ruthenium. It has been pointed out that the radioactive waste content must be kept below 20% due to the performance of the solidified material, such as its conductivity.

On the other hand, in the ceramic solidification method, the maximum heating temperature is 950°C, which is lower than that in the vitrification method, so the volatilization of cesium etc. can be prevented to that extent, so it is necessary to collect and absorb these harmful volatile components. It is advantageous in terms of safety and economy in that it can simplify the process, and it also reduces density by approximately
It is advantageous in that it can be 1.1 times more densified, which allows for volume reduction, and the thermal conductivity is about twice as large as that of the vitrification method. It was considered to be disadvantageous compared to the vitrification method in that it cannot be completely prevented, but according to the present invention, it can be sealed while being sintered in a stainless steel treatment container with excellent water resistance and heat resistance. This method can fully compensate for the disadvantages mentioned above while retaining the advantages of the ceramic solidification method described above.

As explained in detail above, this invention simultaneously performs sintering and encapsulation within the processing container body, so the processing container main body immediately becomes the final processing container, which is extremely economical and rational. As a result, it is possible to prevent the radioactivity-containing powder from being dispersed as much as possible, so that it can be processed even more safely.

Furthermore, the solidification treatment container can completely fulfill the purpose of enclosing the sintered body, and even if it is left to cool in the cooling tank after the sintering treatment, the contents inside will not leak, rust, or scorch. Since there is no fear that the container will crack during subsequent storage, it is possible to achieve the effect that the contained waste will not leak outside.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is a system diagram thereof, and FIG. 2 is a sectional view of the same processing container. 2...Press mold, 3...Mixture, 4...Molded product, 5...Processing container body, 6...Lid, 7...Processing container.

Claims (1)

[Claims] 1. In solidifying radioactive waste, the radioactive waste is burnt using a sintering means to form powder and granules,
A mixture of the powder and the ceramic forming substance at an appropriate mixing ratio is pressed in a press mold to form a mixed molded product, and this mixed molded product is made of a material with high water resistance and heat resistance. Then, a cylindrical lid made of the same material is fitted to the processing container body, and this is stored in a hot press to form ceramics. By pressurizing from above and below at the temperature and pressure necessary for A method for solidifying radioactive waste, which is characterized by simultaneously forming a body and enclosing it in a container. 2. Claim 1, characterized in that the lid to be press-fitted into the processing container has a cylindrical shape and is sharpened at an acute angle by obliquely cutting the inside of the leading edge of the lid. Disposal method of radioactive waste described. 3. A cylindrical processing container body with an open top made of a water-resistant and heat-resistant material, and a cylindrical lid with an open bottom made of the same material as the processing container body which is inserted into the processing container main body. A solidification treatment container for radioactive waste, characterized in that the lid body is sharply pointed by cutting the inside of the tip edge diagonally.