JPS58146898A - 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, 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-forming material is formed by heating and firing. The present invention relates to a method for manufacturing a radioactive waste storage body that is chemically and mechanically stable and suitable for semi-permanent storage by impregnating a porous sintered body with molten metal.

[Technical background of the invention]

With the spread of nuclear power generation, highly concentrated radioactive waste fluid generated from spent nuclear fuel reprocessing plants is increasing year by year, and there are safety issues in storing these radioactive waste fluids in their 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 solidified in a form that minimizes the daily diffusion of radioactive materials, 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 currently proposed at home include ceramic solidification (for example, JP-A-Sho!;!-/u++ No. 7, JP-A-12441, JP-A No. 12441, JP-A No.
s L ruoo, No. 33-904I4J, etc.). This method involves adding an appropriate amount of a ceramic-forming substance such as alumina, silica, or titania to a calcined body of radioactive waste, compression molding it, and then heating and firing it to produce a solidified ceramic body of a certain shape. It is something.

[Problems with background technology]

According to the conventional ceramic solidification method described above, by firing at a high temperature of usually 1200°C or higher, it is possible to obtain a sintered body that has relatively high mechanical strength, is dense, and has excellent water resistance. However, it has the following problems.

b) In general, the lower the firing temperature is, the easier it is to produce a solidified product, and it is advantageous in terms of reducing the burden on firing equipment such as a furnace. Therefore, it is desirable to be able to form a sintered body at a relatively low temperature of 1,100°C or lower. However, according to the research of the present inventors, the composition range of the ceramic building materials that have been published so far shows that it is possible to form a sintered body at a temperature of 7,100°C or lower. After one firing, only a mechanically weak and porous sintered body was returned.

(b) Cera2Tsuku solidified material is susceptible to mechanical shock, and assuming that the storage container for the solidified material is damaged, the solidified material may come into direct contact with the external atmosphere 1, for example, groundwater in the case of underground storage. Therefore, it is recommended to reduce the rate of radioactive substances leaching into the external atmosphere such as water as much as possible.

(c) Since the ceramic solidified body has essentially low thermal conductivity, the heat generated due to the radioactive decay of the radioactive substance contained in the solidified body is insufficiently dissipated.

This causes problems such as internal deterioration due to temperature rise inside the solidified body and the escape of highly volatile substances to the outside, making it difficult to safely store radioactive waste over a long period of time.

[Purpose of the invention]

The present invention eliminates the drawbacks of the conventional cellar solidification method as described above, and produces radioactive waste that has excellent mechanical strength, chemical stability, and heat dissipation properties, and can be safely stored for a long period of time. The object of the present invention is to provide a method for manufacturing a storage body.

[Summary of the invention]

According to the research of the present inventors, a mixture of a calcined body of radioactive waste and a ceramic-forming substance is heated at 7200°C to form a radioactive waste material with superior mechanical strength and heat dissipation properties compared to conventional ceramic solidified bodies. It has been found that a reservoir is obtained. In other words, the method for treating radioactive waste of the present invention involves adding ~% by weight to the calcined radioactive waste and ~% by weight of the slag-forming substance to ~.
60 weight -, molded, heated and fired at a temperature of 900-1100°C to form a porous sintered body, and the porous sintered body is charged into a container, and the molten metal is heated in the container. The method is characterized by comprising a step of impregnating the porous sintered body with the porous sintered body and solidifying the porous sintered body.

[Detailed description of the invention]

The present invention will be explained in more detail below. In the following description, "parts" and "96" are based on weight unless otherwise specified.

The radioactive waste to be treated by the present invention includes, for example, radioactive waste remaining after O and Pu are recovered after processing spent nuclear fuel, as well as concentrated liquid of recycled waste liquid from a mixed bed desalter, Various waste liquids containing radioactive substances such as concentrated waste liquid from floor drains or equipment drains generated from buildings, as well as used ion exchange resins generated from various systems such as atomic r water purification systems, fuel pool systems, condensate systems, and drain systems. filter sludge.

It includes high-level, medium- and low-level radioactive wastes, such as various solid wastes such as sedimentation sludge produced by coagulation and sedimentation treatment of waste liquids. By calcining these radioactive wastes, a calcined body can be obtained as a raw material. On the other hand, Muyu, O,, 81Q,, k
8rO, ZrO, Tie, or a mixture of some or all of these oxides.

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 body. , m-IAo % is suitable. In accordance with the present invention, first, the above-mentioned calcined body powder and ceramic powder are mixed, pressed and formed into a certain shape, and then fired at a temperature of too -1ioot to form a porous material. Form a sintered body. When firing at a temperature below 100°C, the calcined body powder and the ceramic-forming substance react to form a chemically stable compound, and the firing is often completed without any reaction. . On the other hand, if the sintered body is fired at a temperature of /200'C or higher, the sintered body becomes less porous and impregnated with molten metal becomes difficult.

Regarding the pressure during firing, it is generally sufficient to perform firing under normal pressure. Although pressure can be applied to increase the strength of the sintered body, it is preferable that the pressure be applied to a level that imparts porosity to the sintered body.

Next, the obtained porous sintered body is charged into a container, and the porous sintered body is impregnated with molten metal in the container, and then cooled and solidified. Methods for impregnating lW molten metal into a porous sintered body include (a) a method in which molten metal is poured into a container charged with a porous sintered body; A method is used in which the metal is charged into a container and then heated to melt the metal inside the container.

Furthermore, in order to promote impregnation of the molten metal into the porous sintered body, it is preferable to take the following method.

(a) A method in which impregnation with molten metal is started while maintaining a container containing a porous sintered body at a degree of vacuum of io atmospheric pressure or less.

(1)) A method in which molten metal is impregnated into a porous sintered body and pressurized at a pressure of up to 100 atmospheres during the solidification process.

As the metal material for impregnation, Ou, 1., Mu1. Ga.

An, jn, Ii and alloys containing at least one of these metals as a main component are suitable.
Fb when using molten metal in a container made of u.

! In, Kn, Mu1, and alloys containing at least one of these metals as a main component are suitable.

Materials for the container into which the sintered body is charged include, for example, C, M1,
．． Ou, Ii, Ti, zr, or an alloy containing at least one of these as a main component is used. For example, as a metal material impregnating a porous sintered body (U-ZN alloy (anso-arrogant, znso-
), consider the melting point and mechanical strength, and ν
e.

Ou, Ni, Ti, Zr, or an alloy containing at least one of these as a main component is preferably used.

As for the size of the container, the larger the volume, the more radioactive waste can be solidified, but if it is too generous, 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 preferably kzsOwm, and the wall thickness of the container is resistant to thinning due to thick corrosion, and is also advantageous in terms of mechanical strength.
As the thickness increases, the thermal conductivity decreases, so a range of 0.! to !- is desirable. It is also possible to further bury one or more of the inner container (inner container) in the outer container (storage container) using metal.As a method of trenching, (a) compression molding the inner container with metal powder; Either further sintering if necessary, or charging the inner container into the outer container and heating the entire container to melt the metal inside, then cooling and solidifying. ←) After charging the inner container into the outer container, the molten metal e) conversely, pour an appropriate amount of molten metal into the outer container, then charge the inner container, and then cool and solidify the molten metal. However, even when one or more internal contents are buried, it goes without saying that it is desirable to place them at an appropriate distance from each other, and to place them near the center of the external container to isolate them from the outside world as much as possible.

As the material of the outer container, for example, 1.,mu1゜Cu
, Pb, Brs, Zn, lii, T
i, Zr, or an alloy containing at least one of these as a main component, which is appropriately determined depending on the solidification method and burial method8. For example, CuJn alloy (0u30%, Zn5Y )fk)
When embedding an inner container impregnated and solidified in an outer container by melting, the melting point and mechanical strength should be considered.

AI, ou, Ii, Ti, Xr, or an alloy containing at least one of these as a main component is preferably used.

After the solidification step and the burying step, a lid made of the same material as the inner container and the outer container is respectively placed on the container, and the periphery is sealed by welding or the like.

The radioactive waste storage body obtained by the method of the present invention as described above has a structure as shown in the drawings, for example, when seven inner containers are buried in an outer container. That is, the porous sintered body impregnated with metal is solidified together with the metal in the inner container, and the inner container is further buried completely in the metal at approximately the center of the outer container II3.

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. In other words, in the case of the storage body according to f14 of the present invention, even if the storage container (external container) J is damaged, the porous sintered body formed from radioactive waste and ceramic forming material is impregnated with metal. / is further isolated from the external atmosphere, such as numbing water, by the buried metal parts and the inner container, so there is extremely little risk of direct contact with the external atmosphere. Considering the extremely small leaching rate of metals into water, long-term safe storage can be ensured even in the event of the damage to the Totodate storage container mentioned above. In addition, even if the internal container is damaged due to water intrusion through the installed metal pipe, the inner container will be protected even if the internal container is damaged. It is isolated from the outside world because it is surrounded by trees. Furthermore, even if the inner container is damaged, the porous sintered material inside is impregnated with metal, so it is mechanically strong and far superior to a solidified material made of porous sintered material. ing.

[Examples and comparative examples of the invention]

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

Calcined powder of the simulated radioactive waste mentioned above, mu x, o,
<y96. SiO*u%, Be, Ojr%,
BrO, 1%.

After uniformly mixing the ceramic building material powder consisting of ZRO, J%, and TLO at a weight ratio of 3:3, it was put into a mold and compressed with a pressure of 7cm/ton, and was molded to a diameter x height. A cylindrical molded body of approximately 30 parrots was obtained. This molded body was fired at a temperature of 1000°C for 1 hour to a diameter of approximately U.
A cylindrical porous sintered body having a height of JJ'w was obtained. The porosity of the sintered body was approximately 16%. This porous sintered body has an inner diameter of
A parrot was placed in a nickel cylindrical container with a wall thickness of Jm and a height of 40 cm, and an Ou-Rn alloy (0u50
%, Zn30%) powder. This cylindrical nickel container was placed in a vacuum heating furnace and heated at 900°C for 1 hour in a vacuum degassing atmosphere below 10-" atmosphere to melt the alloy, and then inert while heating. The gas was introduced into a vacuum heating furnace and returned to atmospheric pressure, and the molten metal was impregnated into the porous sintered body, which was then cooled and solidified.Furthermore, a nickel cylinder with diameter x exfoliation and wall thickness! The inner lid was dropped, the surrounding area was sealed by T-G welding, and the area above the welded part was cut off.Next, the above nickel container (inner container) was placed in a stainless steel container with an inner diameter of yW and a height of SO, and the surrounding area was sealed. After wrapping and covering with copper powder having a particle size of 100 or less, it was compressed at 4 tons/ls'' and further sintered at 100° C. for 1 hour in a hydrogen stream.

The storage container (outer container) was removed from the storage body thus obtained to expose the internal solid body.

When this was immersed in pure water 10011 at 100°C for 1 hour and a leaching test was performed to detect λ ions in the solution, the leaching rate was less than the detection limit / y 10 I/3+''・mu 1. The leaching of storm ions contained in the simulated waste also had a detection limit of /x/DI of less than +LIL7.

Furthermore, zwxytl■X10T from the center of the nickel container
A rectangular parallelepiped compression test piece of IIIL was cut out and subjected to compression fracture desiccation, and the compressive strength was found! rOi" or more, and the mechanical strength was great.

Comparative Example Calcined powder of simulated radioactive waste used in Example and Mu1
, 0.4c6% , 810. @;)%, BaO!
%, Br01-.

ZrO! Ceramic forming material powder consisting of J%, Tie, and J2 is mixed uniformly in a weight ratio using a Jnige, and then put into a mold and compressed with a pressure of /ton/cII4'', and is made into a material with a diameter of X and a height of X. A cylindrical molded body was obtained.This molded body was fired at a temperature of 1000°C for 1 hour to have a diameter of approximately U.
(2) A cylindrical porous sintered body with a height of approximately Llms was obtained. The obtained porous sintered body was placed in a nickel cylindrical container with an inner diameter of 30 ym, an inner thickness of 1 m, and a height of 60 wm, and packed with copper powder of less than 100 mesh islands and compressed with a pressure of 4 tons/α1.
Furthermore, inside the nickel cylinder, it has a diameter of 1.5 mm and is thick! The nickel inner lid of (2) was dropped, the surrounding area was sealed by τIG welding, and the portion above the welded portion was cut off. Next, the above sealed nickel container was placed in a stainless steel container with an inner diameter of y-1 and a height of 9-1, and the surrounding area was covered with copper powder of less than 100 mm, compressed at a pressure of 4 tan/cps, and further hydrogenated. Sintering treatment was performed at 100° C. for 1 hour in an air stream.

The storage container (outer container) was removed from the storage body thus obtained to expose the internal solid body. This is 10
Soaked in 100 d of pure water at 0°C for 1 hour.

A leaching test was conducted to detect crude ions in the solution, and the leaching rate was below the detection limit.
It was less than ay. In addition, the ions contained in the simulated waste were also less than the detection limit / X 10 I /cIM''・muy.However, in a rectangular parallelepiped compression test of 1m When a piece was cut out, the compressive strength was less than jkg/am''K and the mechanical strength was low.

〔Effect of the invention〕

As is clear from the above-mentioned Examples and Comparative Examples, in the storage body of the present invention, the periphery and inside of the pores of the porous sintered body obtained by firing at a relatively low temperature of 7200°C or less are impregnated and solidified with metal. To be there.

It has excellent heat dissipation properties and is mechanically and chemically stable.

Furthermore, even if the outermost storage container is damaged and the internal solid material is misted out, the storage body of the present invention does not allow the solidified radioactive elements to leach out, and is a mere cellulose container. It is safer and has better long-term storage than solidified materials.

[Brief explanation of the drawing]

The drawing is a longitudinal section through a storage body obtained by one embodiment of the method of the invention. C. A porous sintered body obtained from calcined radioactive waste and a ceramic-forming material impregnated with metal and solidified.
C...inner container, J...outer container, D...metal for burial. Applicant's agent Kiyoshi Inomata

Claims (1)

[Claims] / After mixing and molding calcined radioactive waste J-1 by weight and 10 to 60 wt % of a ceramic forming substance w ~1
A step of heating and firing at a temperature of ioo°C to form a porous sintered body, and charging the porous sintered body into a container, impregnating the porous sintered body with molten metal and solidifying it in the container. A method for disposing of radioactive waste characterized by comprising steps. λ, the method of treating radioactive waste according to claim 1, characterized in that impregnation with molten metal is carried out while maintaining the container containing the porous sintered body in a vacuum of IO atmosphere or less. J, Impregnation and solidification of molten metal into porous sintered body,
The method for treating radioactive waste according to claim 7 or 2, which is carried out under a pressure of / -100 air pressure. The radioactive waste according to any one of claims 1 to 3, further comprising the step of further embedding at least one portion of the container containing the porous sintered body impregnated with metal in metal in an outer container. How to process things.