JPS6046395B2 - Method for producing solidified radioactive waste containing ruthenium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing solidified radioactive waste containing ruthenium, more specifically, a method for producing solidified radioactive waste containing ruthenium, which fixes ruthenium inside, is chemically and mechanically stable, and is a semi-permanent material for radioactive waste containing ruthenium. The present invention relates to a method for producing a solidified material suitable for commercial storage.

As the contribution of nuclear power generation to electricity supply increases, the amount of highly concentrated radioactive waste generated from spent nuclear fuel reprocessing plants is increasing year by year.

- Storing these waste liquids in tanks as they are poses safety and management problems. Therefore, there is a strong desire to establish a technology for converting waste liquid into a solid storage medium that can be stored more safely. Generally, when solidifying radioactive waste, the waste is solidified in a form that minimizes leakage into the surrounding environment, and the resulting solid storage medium is chemically and mechanically stable. Therefore, it is necessary that it does not cause environmental pollution even when stored for a long period of time. Conventionally used solidification methods include vitrification technology (for example, 1973-32 Sengo, 50-50).
48 compatibility) is the mainstream.

That is, highly concentrated radioactive waste, which is normally generated as a nitric acid solution, is calcined to remove the evaporated components, and the highly concentrated radioactive waste is separated in the form of nitrate or oxide powder. This is a method in which the powder is melted together with phosphoric acid or a glass such as borosilicate glass, and then solidified by solidifying into an ingot of a certain shape. However, conventional vitrified materials that have been widely used have the following drawbacks.

For example, when solidified waste is stored in seawater, for long-term safe and stable storage, it is necessary to keep the leaching rate of radioactive waste from the storage container as low as possible. . In this respect, since the vitrified material is limited by its basic material, glass, it is necessary to consider other materials in order to further reduce the leaching rate. In addition, the thermal conductivity of glass is lower than that of metals, so when the radioactive substances it contains generate heat due to radioactive decay, the amount of heat is accumulated in the vitrified body, and in the center of the solidified body, 5
The temperature may rise to 00-700°C.

As a result, the vitrified body becomes brittle and its mechanical strength decreases, making it difficult to store radioactive waste for a long period of time.
Furthermore, glass-based materials inherently have the disadvantage of low thermal shock resistance and mechanical shock resistance, and since it is difficult to improve these, extreme care must be taken when transporting and storing vitrified materials. It was hot. As other solidification methods, storage bodies using ceramics, which originally have a low leaching rate and excellent corrosion resistance, are being considered.

Although this storage body overcomes the drawbacks of the vitrified body mentioned above and is suitable for long-term safe storage, it is generally manufactured by sintering at a high temperature of 1000°C or higher. However, the drawback is that ruthenium oxide, which is a component of radioactive waste, is scattered during the sintering process.
In order to eliminate the above-mentioned drawbacks in the production of ceramic solidified bodies of radioactive waste containing ruthenium, the present inventors have conducted intensive research and found that a predetermined amount of oxidation We discovered that when ferrous iron (FeO) is added and sintered in an atmosphere with low oxygen partial pressure, ruthenium is prevented from scattering and fixed in the solidified body, and we have completed the present invention. .

An object of the present invention is to provide a method for producing a solidified ceramic body that can safely store radioactive waste containing ruthenium for a long period of time.

The method of the present invention includes: a calcined powder of radioactive waste containing ruthenium; and at least one powder selected from the group of aluminum oxide, silicon oxide, strontium oxide, barium oxide, titanium oxide, zirconium oxide, and calcium oxide; 1 to 5% by weight of ferrous oxide powder based on the total weight is mixed, the resulting mixed powder is pressurized to form a green compact, and the green compact is then heated to an oxygen partial pressure of 10-2 atmospheres or less. It is characterized by being solidified in an atmosphere of

In the method of the present invention, the calcined bodies of radioactive waste to be treated include the remaining radioactive waste from which U and Pu have been recovered after processing spent nuclear fuel, and concentrated recycled waste liquid from a mixed bed desalination device. Various waste liquids containing radioactive substances, such as concentrated waste liquid from floor drains and equipment drains generated from buildings; or used ion exchange resins generated from reactor purification systems, fuel pool systems, condensate systems, and drain systems. Includes calcined bodies made from high-concentration and medium-low concentration radioactive waste, such as filter sludge and various solid wastes such as precipitated sludge produced by coagulation and sedimentation treatment of waste liquid.

The obtained calcined body is in the form of a powder or a "koji-like" shape, but it is preferable to crush the calcined body by a conventional method and use it as a powder with an appropriate particle size.

In the method of the present invention, first, the powder of the above-mentioned calcined body and the powder of at least one kind of powder selected from the group of aluminum oxide, silicon oxide, strontium oxide, barium oxide, titanium oxide, zirconium oxide, and calcium oxide are mixed and oxidized. Mix the ferrous powder. Here, at least one powder selected from the group of aluminum oxide, silicon oxide, strontium oxide, barium oxide, titanium oxide, zirconium oxide, and calcium oxide (hereinafter referred to as a ceramic-forming substance) used in the present invention is It is an inorganic compound that forms a ceramic sintered body by sintering, which will be described later, together with powder.

When used, a mixture of some of these inorganic compounds may be used.

All of these are used in the form of powders with appropriate particle sizes. One of the features of the present invention is the inclusion of ferrous oxide powder.

The blending amount of the ferrous oxide is 1% based on the total weight of the mixed powder.
If the amount is less than 1% by weight, it will not be possible to prevent ruthenium from scattering during sintering, and if it exceeds 5% by weight, it will not be possible to prevent ruthenium from scattering during sintering. Partial melting of the solidified material is undesirable. Mixing of the above three components is carried out according to a conventional method.

The obtained mixed powder is filled into a predetermined mold, for example, 50
A compact is formed by applying a pressure of 0 to 1000 kg1d. Next, the green compact is heated and sintered at a temperature of 1000 to 1350°C in an atmosphere with an oxygen partial pressure of 10 −2 atmospheres or less to form a solidified body.

At this time, if the oxygen partial pressure exceeds 10 −2 atmospheres, it is not preferable because ruthenium will not be fixed or remain in the solidified material obtained by scattering the ruthenium. The method of the present invention will be explained below based on examples.

Example After processing spent nuclear fuel, we simulated the composition of the calcined body of the remaining radioactive waste from which U and Pu were recovered. %) was prepared (hereinafter referred to as 1 simulated calcined body).

). Ceramics-forming substances include: Al2O3:4
5% by weight, SlO2: 45% by weight, SrO: 10% by weight
A mixed powder consisting of was used.

Nine types of mixed powders were prepared by mixing the simulated calcined body, the ceramic forming material, and the FeO powders at the compounding ratios shown in Table 2.

All powders had an average particle size of 2 μm or less. Each 30y of the obtained mixed powder was filled into a predetermined mold, and 1000y
Apply a pressure of 91d, vertically 30? , thickness approximately 20TII
A plate-shaped green compact of m was molded. Next, this green compact was sintered under various conditions shown in Table 2 to obtain a solidified body.

The porosity of each solidified body obtained was measured by a conventional method,
The presence or absence of Ru was also measured by fluorescent X-ray analysis.

The results are collectively shown in Table 2. As is clear from the above results, it was found that in the solidified bodies (Examples 1 to 5) manufactured by the method of the present invention, Ru was fixed inside without scattering.

Claims (1)

[Claims] 1. A calcined powder of radioactive waste containing ruthenium, and at least one powder selected from the group of aluminum oxide, silicon oxide, strontium oxide, barium oxide, titanium oxide, zirconium oxide, and calcium oxide;
1 to 5% by weight of ferrous oxide powder based on the total weight is mixed, the resulting mixed powder is pressed to form a green compact, and then the green compact is heated to an oxygen partial pressure of 10^-^2 A method for producing a solidified radioactive waste containing ruthenium, which comprises sintering in an atmosphere below atmospheric pressure to form a solidified body.