JPS58160899A - Method of processing radioactive waste - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for disposing of radioactive waste, and more specifically, a mixed powder of a radioactive waste calcined body and a ceramic building material is formed, and then heated and fired. This invention relates to a method of manufacturing a radioactive waste storage body that is chemically and mechanically stable and suitable for semi-permanent storage by embedding a dense sintered body formed by the method in metal.

[Technical background of the invention and its problems]

With the spread of nuclear power generation, highly concentrated radioactive waste fluid generated from spent nuclear fuel reprocessing plants tends to increase every year, and there are safety issues in storing these radioactive waste fluids in liquid form in tanks. Therefore, there is a strong desire to establish a technology to convert it into a solid storage medium that can be stored more safely.

Generally, when disposing of radioactive waste, the waste is converted into a form that minimizes the diffusion of radioactive substances into the surrounding area, and the resulting solid storage medium is chemically and mechanically stable. It is necessary that long-term storage does not cause environmental pollution. From this point of view, ceramic solidification methods have been proposed to date (for example, JP-A No. 55-1, No. 1, No. 1, No. 33-1).
7/θO, 1tj-90'14J, etc.), this method involves adding appropriate amounts of, for example, alumina, silica, and Ceric-forming substances from Titania to a calcined body of radioactive waste. A ceramic assimilated body of a certain shape is produced by adding the powder, compression molding, and heating and firing.

According to the conventional ceramic solidification method as described above, a sintered body having relatively high mechanical strength and excellent water resistance can be obtained, but the following problems remain.

Q) In general, it is easy to produce a solidified product with a low temperature, and it is advantageous in terms of reducing the burden on firing equipment such as a furnace, but according to the research of the present inventors, In the composition range of the ceramic-forming materials used, firing at temperatures below 1-00 DEG C. will only result in mechanically weak, porous sintered bodies.

(b) The fired sintered body is usually charged into a container and stored as is. Therefore, sintered bodies are produced to match the size and shape of the storage container, but generally, sintered bodies have unevenness on the surface and darkening of dimensions due to uneven temperature distribution in the furnace during firing. When this material is directly charged into a storage container, it is inevitable that a void will be created between the sintered material and the container.Due to this void, radioactive materials contained in the sintered material will decay. This results in insufficient dissipation of the heat to the outside of the container, resulting in problems such as an increase in the temperature inside the sintered body, which causes internal deterioration and highly volatile substances to escape to the outside. In order to avoid this problem, it is conceivable to process the sintered body to match the shape of the container by cutting. However, it is technically difficult to process sintered bodies containing radioactive materials, and cutting and the like produce fine powder of radioactive materials as secondary waste.

(c) Ceramic solidified bodies are generally weak against shock, and assuming that the storage container for the solidified bodies is damaged, the solidified bodies will come into direct contact with the external atmosphere, such as groundwater in the case of underground storage. It is required to reduce the leaching rate of radioactive substances into the external atmosphere such as water as much as possible.

[Purpose of the invention]

The present invention aims to solve all the problems of the conventional ceramic building solidification method as described above, and has excellent mechanical strength, chemical stability, and heat dissipation, and can be stored safely for a long period of time. The purpose of the present invention is to provide a method for manufacturing a radioactive waste storage body.

[Summary of the invention]

According to the research of the present inventors, in order to achieve the above-mentioned object, a mixed powder of calcined radioactive waste and a ceramic material is molded into a dense powder that is expanded by heating and firing. It has been found that it is extremely effective to charge the sintered body into a container and then fill the gap between the sintered body and the container with metal to form a composite solidified body consisting of gold-ceramic sintered body. . That is, the radioactive waste treatment method of the present invention comprises calcined radioactive waste a-U weight, 11% and ceramic forming material ♂o-b.
A step of mixing and molding the mixture and then heating and firing the mixture at a temperature of θ0°C or higher to form a dense sintered body.

This method is characterized by the step of charging the sintered body into a container, filling the gap between the container and the sintered body with molten metal, and solidifying the molten metal.

[Detailed description of the invention]

The present invention will be explained in more detail below. In the following description, "parts" and "parts" are based on weight unless otherwise specified.

The radioactive waste to be treated by the present invention includes, for example, after processing spent nuclear fuel, Radioactive materials such as concentrated waste liquid from floor drains or equipment drains generated from buildings [including various waste liquids, as well as used ion exchange resins generated from atomic water purification systems, fuel pool systems, condensate systems, and drain systems; It includes high-level and medium-low-level radioactive wastes, such as various solid wastes such as filter sludge and precipitated sludge produced by coagulation-sedimentation treatment of waste liquid.By calcination of these radioactive wastes, calcination as a raw material is possible. You get a body.

On the other hand, as a sera building substance, 1.0g of mu, 81
0. , Bad, 8rO, ZrO,, Te10. Or a mixture of some or all of these oxides is included.

If the content of the calcined body is too small, the waste treatment efficiency will decrease, but on the other hand, if the amount of the calcined body is too large, it will be difficult to form a solidified ceramic body. -IR) fb range is appropriate. According to the present invention, first, the above-described calcined body powder and ceramic-forming substance powder are mixed, compressed and molded into a certain shape, and then fired at a temperature of 1200° C. or higher to form a dense sintered body. If the firing temperature is less than 1-003, the sintered body tends to become porous, making it difficult to obtain a dense sintered body. Generally, the more porous the sintered body is, the less waste can be treated, which is inappropriate. Furthermore, especially if the firing temperature is lower than 100°C, the calcined body powder and the ceramic building material will not react to form a chemically stable compound, and the firing will end without any reaction. There is also.

Normal pressure is usually sufficient for firing, but it is also preferable to pressurize to obtain a denser sintered body.Generally, the sintered body obtained under the above conditions is dense and has good mechanical strength and water resistance. It's not neat.

Next, the sintered body thus obtained is placed in a container, and the gap between the sintered body and the container is filled with a fly. FIG. 1 is a longitudinal sectional view of an example of a storage body obtained in this manner. More specifically, first, the sintered body I obtained by the method described above was charged into a container, and the gap between the container 2 and the sintered body I was filled with a gap-filling metal 3, and the gap was sealed. After cooling, solidify. Methods for filling metal include pouring molten metal into a container; ←) Metal powder (granules) is charged into a container together with a sintered body, heated from the outside to melt the metal inside, and then cooled and solidified. The method used.

From the viewpoint of meltability within the heat-resistant temperature range of the container material, examples of gold and steel materials for filling voids include Ou, Fθ, Mu1. PI).

Suitable materials include Sn, Zn, Ni, and alloys containing at least one of these metals as a main component. For example, Ou
When using molten metal in a container made of Pb, Eln
.

Suitable materials include Kn, Mu1, and alloys containing at least one of these metals as a main component.

As for the size of the container, the larger the volume, the more radioactive waste can be solidified, but if the container is too large, the thermal conductivity and mechanical strength will decrease, which is not preferable. For example, in the case of a cylindrical container, the inner diameter is j −! r00s
ow is desirable, and the thicker the wall thickness of the container, the more durable it is against wall thinning due to corrosion, and is also advantageous in terms of mechanical strength, but if it is too thick, the thermal conductivity will decrease, so O, S ~
A range of 10 m is preferable, and if necessary, as shown in FIG. Alternatively, it can be further embedded using metal in a storage container (external container). FIG. 2 is a longitudinal cross-sectional view of seven inner containers embedded in an outer container. That is, the sintered body l is solidified together with the metal in the inner container a, and this inner container is further solidified with the embedding metal at the approximate center of the outer container. It is buried inside. As a result of being coated multiple times with metal in this way, the radioactive waste storage body according to the present invention has extremely high mechanical and chemical stability, and is suitable for long-term safe storage.

As for the method of burying the inner container in the outer container, (a)
A method in which the inner container is compression molded together with metal powder and further sintered if necessary, or the inner container is charged into an outer container and heated together to melt the gold m inside, and then cooled and solidified.61
1t) A method in which the inner container is charged into the outer container, molten metal is poured into the container, and then cooled; (c) Conversely, an appropriate amount of molten metal is placed in the outer container, and then granules are charged. A method of cooling and solidifying molten metal is used. However, even when two or more inner containers are buried, it goes without saying that it is desirable to space them appropriately apart from each other and place them near the center of the outer container to isolate them from the outside world as much as possible.

Examples of the material for the outer container include F., Mu1. Ou
.

Pb, Eln, Zn, Ni, Ti, Zr
Alternatively, an alloy containing at least one of these as a main component may be used, and the container may be further filled with an empty Vflfou with a sintered body, which is determined as appropriate depending on the solidification method or burial method. When embedding molten PBT in an external container, considering the melting point and mechanical strength, Ou, Ni, Ti, Zr, or an alloy containing at least one of these as a main component is preferably used.

After the above-mentioned solidification and burying steps, lids made of the same material as the inner container and the outer container are respectively covered, and the periphery is sealed by welding or the like.

In the radioactive waste storage body obtained by the method of the present invention as described above, even if the storage container (external container) is damaged, the sintered body can be buried with the filling metal aS. Since it is isolated from the external atmosphere, such as seawater, by the internal container, there is very little risk of direct contact with the external atmosphere. Considering the extremely low leaching rate of the water sacs of gold tanks, long-term safe storage is ensured even in the event of the above-mentioned damage to the storage container. In addition, even in the unlikely event that the internal container is partially damaged or flooded through water, the dense sintered body made from the calcined radioactive waste and ceramic-forming material will remain intact inside the container. Because the gap between the container and the container is filled with metal, the dissipation of radioactive materials due to water intrusion is not only much smaller than when the sintered body is simply stored in the container, but also the dissipation of radioactive materials is much lower. It also has excellent strength and mechanical strength.

[Examples and comparative examples of the invention]

Example A calcined powder of simulated radioactive waste having the composition shown in the table below (simulating the oxide obtained by calcining waste liquid from a reprocessing plant) was prepared.

The calcined powder of the simulated radioactive waste mentioned above and the mu1,0,
4191, Elio, 416%, BaOj%, Br
Ceramics forming material powder consisting of Oj %, Zr 0.19b, Tie, j % in weight ratio was uniformly mixed with J: Ri, and then gold a! ! The molded product was placed in a container and compressed at a pressure of 7 tons to obtain a cylindrical molded product with diameter x height x height. This molded body was fired at 7130°C for 2 hours to obtain a diameter of approximately
A fine cylindrical sintered body with a height of about 8 cm was obtained. This sintered body was placed in a nickel cylindrical container having an inner diameter JOm, a wall thickness JOm, and a height 60ax, and was filled with 10θ mesh and Cu powder as shown below. This nickel group cylindrical container was heated in a hydrogen atmosphere at 1110° C. for 30 minutes to melt the O, and the sintered body and the empty space in the container were filled with molten O, and then cooled and solidified.

Furthermore, the diameter inside the nickel cylinder? Just under 6am, thick ja
The inner diameter of the nickel container was removed and the surrounding area was sealed by T welding. ; Placed in a stainless steel container with a size of 0m51 and a diameter of 50cm, the surrounding area was covered with a mesh and the following blunt powder, then compressed at a pressure of 6 tons, and further sintered at 100℃ for 1 hour in a hydrogen stream. I then covered it with a stainless steel lid and TIG welded it. The storage container was removed from the storage body thus manufactured to expose the internal container.

Furthermore, use an ultrasonic drill to drill the center part of the side of the inner container with a diameter of approx. ■Drill a hole with a depth of about /am and insert it into the JO
When the MO ions eluted after being kept in a boiling water bath (Tate ± 1°C) for 1 hour were analyzed by ZOP emission spectroscopy, the concentration was 0. J ppm or less.

Comparative Example Calcined powder of simulated radioactive waste used in Example and 11
10B 41-0%, 8101%, BaOz%, 8
Ceramic-forming material powders consisting of rOj, ZrO, A cylindrical molded product of 30 rugs in size was obtained. This molded body was fired at a temperature of 7000° C. for several hours to obtain a cylindrical porous sintered body with a diameter of about Jigm and a height of about 2 g.

The obtained porous sintered body has an inner diameter of X) g, a wall thickness of su, and a height of 4
01111, packed with copper powder of less than /θ0 Messi Island and compressed with a pressure of 4 tons//1 Mp, and further placed in a nickel cylinder with a diameter of X) wm, weak,
Drop the inner pig made of 2V KEL with wall thickness I■, and check the surrounding area? I.G.
The nickel container, which has been sealed by welding and the upper part above the welded part is cut off, is placed in a stainless steel container with a height of 50mm and the surrounding area is covered with 100 mesh, and the following copper powder is applied. After removing the bitterness, it was compressed under a pressure of 4 tons, and then sintered at 100° C. for 1 hour in a hydrogen stream. Furthermore, this was covered with a stainless steel 7 tab and sealed by Xa welding.

The storage container was removed from the storage body thus obtained to expose the inner container. Furthermore, use an ultrasonic drill to drill the center part of the side of the inner container with a diameter of approx. Deception, depth approx. 1
After making a hole of 0.0 mm and keeping it in a 300 cc boiling water bath (at 9±/℃) for 1 hour, the eluted MO ions were analyzed by xcp emission spectroscopy, and the concentration was about λppm. Ta.

〔Effect of the invention〕

As is clear from the above-mentioned Examples and Comparative Examples, the radioactive waste storage body obtained by the method of the present invention is obtained by charging a dense sintered body obtained by firing at a temperature of /MO°C or higher into a container, Because it is filled and solidified with metal, it has excellent heat radiation and is mechanically and chemically stable. Furthermore, in the storage body of the present invention, even if the outermost storage container is damaged and the internal solid body is exposed, the radioactive elements solidified inside are extremely unlikely to leach out, and the storage body is simply sintered. It is safer and has better long-term storage than storing the body in a container.

[Brief explanation of drawings]

1 and 1 are longitudinal cross-sectional views of a storage body obtained by the method of the invention. l...A dense sintered body formed by firing a calcined body of radioactive waste and a Cerasec forming material.
Inner container, J...Metal for void filling, J...Outer container, L...Metal for burial. Applicant's agent Kiyoshi Inomata and I 2

Claims (1)

[Claims] 1. Calcined radioactive waste! A step of mixing and molding the 6-m weight bag and the ceramic building material to-to-weight bag, and then heating and kneading the mixture at a temperature of 00° C. or higher to form a dense sintered body; A method for disposing of radioactive waste, comprising the steps of: charging a compact into a container; filling a gap between the container and the sintered compact with molten metal; and solidifying the molten metal. (h) The method for disposing of radioactive waste according to claim 1, wherein at least one of the containers for storing the sintered body embedded in the metal further serves as a metal catalyst in an outer container.