JP3172324B2 - Radioactive gas immobilization equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radioactive gas immobilization apparatus for ionizing radioactive gas generated in a nuclear fuel reprocessing plant or the like and injecting the gas ions into a metal for immobilization.

[0002]

2. Description of the Related Art At a nuclear facility such as a nuclear fuel reprocessing plant, a harmful amount of radioactivity should not be released to the environment.
Safety is strictly required compared to other general industries. For example, in a nuclear fuel reprocessing plant that recovers uranium and plutonium from spent nuclear fuel, a radioactive gas containing fission products is generated in a shearing step, a melting step, and the like of the spent nuclear fuel. Among them, the most problematic radioactive gas is krypton 85 (hereinafter, Kr-85).
This Kr-85 has a half-life of about 1
Since it is as long as 0.7 years, development of a technology capable of safely storing Kr-85 for a long time is underway.

The radioactive gas storage methods developed so far include a high-pressure cylinder storage method in which the radioactive gas is stored in a pressure vessel such as a high-pressure cylinder, a zeolite adsorption method in which Kr-85 is adsorbed on zeolite, and a radioactive gas ionization method. There is known an ion implantation method for injecting into a metal structure.

[0004] In the high-pressure cylinder storage method, it is necessary to periodically perform a pressure test of a storage container for storing radioactive gas. Therefore, the stored gas must be transferred to another container each time, and complicated work is required. Required. In addition, the zeolite adsorption method has many problems until practical use because Kr-85 must be treated under high temperature and high pressure.

On the other hand, the ion implantation method can be processed at normal temperature and low pressure, and can be stored as a stable solidified product. Therefore, the ion implantation method is more economical and more stable than the above-described high pressure cylinder storage method and zeolite adsorption method. This is advantageous in terms of sex.

FIG. 11 and FIG. 12 show a conventional radioactive gas immobilization apparatus utilizing such an ion implantation method. As shown in FIG. 11, this immobilization treatment apparatus is roughly divided into an immobilization container 1a having a sealed structure mainly composed of an ion implantation electrode 1 for immobilizing a radioactive gas, and installed facing the inside of the ion implantation electrode 1. And a sputter electrode 2 to be formed.

The ion-implanted electrode 1 has a cylindrical shape with one end opened, and its open end is closed by an anode flange 4 and an anode lid 5 joined via an insulator 3, thereby forming a fixed container 1 a. Have been. Sputtering electrode 2
Is composed of a cylindrical electrode body 2a having an opening at one end with the peripheral wall facing the peripheral wall of the ion implantation electrode 1, and an electrode lid 6 welded to the opening and closed. A double pipe 7 for circulating and supplying cooling water is connected in the inside 2.

[0008] The ion implantation electrode 1 is connected to an ion implantation power supply 8 provided outside the ion implantation electrode 1.
Is electrically insulated from the anode lid 5 of the ion implantation electrode 1 by an insulating material 9 and is connected to a sputtering power source 10 provided outside.

The anode lid 5 of the fixed container 1a has
An air supply pipe 11 for introducing a radioactive gas into the container and an exhaust pipe 12 for evacuating the container with a vacuum pump are connected. Note that a cooling pipe 13 for preventing overheating due to a sputtering phenomenon is provided in close contact with the outer surface of the fixing container 1a.

In such a configuration, the sputter electrode 2
A negative voltage of 1 KV or more is applied to the ion implantation electrode 1 from the sputtering power source 10 and 1 KV is applied to the ion implantation electrode 1 from the ion implantation power source 8.
A negative voltage of V or less is applied, and the radioactive gas is fixed. That is, when the gas pressure in the fixing vessel 1a and the voltage applied to the ion implantation electrode 1 and the sputter electrode 2 satisfy appropriate conditions, the fixing vessel 1
It is known that the radioactive gas in a is ionized,
For example, the gas pressure in the fixed container 1a is set to 10 ⁻¹ to 10
^When a negative voltage of 1 KV or less is continuously applied to the ion implantation electrode 2 and a negative voltage of 1 KV or more is continuously applied to the sputter electrode 2 in a state where the pressure is maintained at ^-3 Torr, the radioactive gas in the fixed vessel 1a is glow discharged. As a result, the electric field is accelerated toward the sputter electrode 2 as gas ions, and collides with the surface of the sputter electrode 2. At this time, sputtered metal is scattered from the sputter electrode 2. This sputtered metal collides with the inner surface of the opposing ion implantation electrode 1 to form a metal accumulation layer 14.

Some gas ions are directly accelerated toward the ion implantation electrode 1 and are implanted into the metal accumulation layer 14. Thus, the radioactive gas introduced into the fixing container 1a is injected into the metal accumulation layer 14 and fixed.

In such an apparatus for fixing a radioactive gas, the sputter electrode 2 is shaved and the ion-implanted electrode 1 is removed.
The metal film into which Kr-85 gas has been injected is accumulated.
Then, when the sputter electrode 2 is sufficiently consumed and thinned,
End the operation.

The metal film 14 into which the Kr-85 gas has been injected is
Each of the fixed containers 1a is transferred to a storage (not shown), and Kr
Store for a long time until -85 is sufficiently attenuated. At this time, K
Since the r-85 gas is immobilized in the stable metal film, it can be safely stored.

[0014]

By the way, in such a radioactive gas immobilization process, the immobilized container 1a after the treatment is stored until the radiation level is sufficiently attenuated. When stored in a storage facility as it is, there is a problem that a large storage space is required due to a large storage volume, and efficient storage and storage cannot be performed.

Further, the sputter electrode 2 for ion implantation
Conventionally, as shown in FIG. 12, for example, a structure in which a rare earth element metal 16 is mounted at a fixed ratio in an annular groove 15 provided in an electrode body 2a made of a transition metal, so that Kr-85 can be efficiently produced. It has been confirmed that gas injection can be performed.

However, if the embedding pitch of the rare earth metal 16 is too large, the formed metal accumulation layer 14
And the injection efficiency of the Kr-85 gas is reduced.

Furthermore, although the efficiency is improved by reducing the embedding pitch, the number of processed annular grooves 15 increases,
There is a problem that manufacturing is not easy.

The present invention has been made in view of such a problem. The present invention has been made to enable storage and storage with a large volume reduction effect in handling of an immobilized container after immobilization processing of a radioactive gas and an apparatus. It is an object of the present invention to provide a safe radioactive gas immobilization apparatus capable of efficiently and economically manufacturing the main constituent members of the present invention and capable of stably performing radioactive gas immobilization processing. .

[0019]

In order to achieve the above object, a first aspect of the present invention is to dispose a sputter electrode on the inner surface of a container-like ion implantation electrode for introducing a radioactive gas, and to interpose a sputter electrode between the two electrodes. A radioactive gas for implanting and accumulating a cumulative layer of sputtered metal emitted from a sputter electrode on the inner surface of the ion-implanted electrode by sputtering effect of the glow discharge, Wherein the sputtered electrode is formed of a composite metal in which particles of a rare earth element are densely dispersed in a matrix composed of a transition metal, and the particle diameter of the powder of the rare earth element is 100 to 2,000.
μm.

According to a second aspect of the present invention, in the apparatus for fixing a radioactive gas according to the first aspect, the transition metal constituting the mother phase of the sputter electrode is made of nickel, copper or another transition metal powder. The rare earth element particles are characterized by being made of powder of yttrium, lanthanum, zirconium or other rare earth metal.

According to a third aspect of the present invention, in the radioactive gas fixing apparatus according to the first or second aspect, the rare earth metal powder is dispersed in the transition metal in a ratio of 10 to 50% by volume. Features.

According to a fourth aspect of the present invention, in the apparatus for fixing a radioactive gas according to any one of the first to third aspects, the composite metal forming the sputter electrode is at least 90% of the theoretical density. It is characterized by the following.

According to a fifth aspect of the present invention, in the apparatus for fixing a radioactive gas according to any one of the first to fourth aspects, the densification of the sputtering electrode is performed at a heating temperature of 400 to 100.
The process is performed at 0 ° C. and a pressure of 100 to 2000 kgf / cm ² .

According to a sixth aspect of the present invention, in the apparatus for fixing a radioactive gas according to any one of the first to fifth aspects, the sputter electrode has a cylindrical shape, and the inside thereof and both ends in the axial direction are made of transition metal. Is also held by a metal layer having a high threshold for sputtering.

[0025]

According to the first aspect of the present invention, since the sputter electrode is formed of a composite metal in which particles of a rare earth element are densely dispersed in a matrix of a transition metal, the transition metal and the rare earth element metal are uniformly formed. By mixing and dispersing, a dense composite metal layer is formed, and the solidified radioactive gas becomes uniform and stable. Therefore, it is possible to perform storage and storage with a large volume reduction effect in handling the immobilized container after the radioactive gas immobilization process, and it is possible to efficiently and economically manufacture the main components of the apparatus, and to reduce the radioactive gas. The immobilization process can be performed stably. If the diameter of the rare earth metal particles dispersed in the transition metal is smaller than 100 μm, uniform dispersion becomes difficult, and if it exceeds 2000 μm, the strength of the electrode body after densification decreases. According to the present invention, densification becomes possible by using rare earth metal particles of 100 to 2000 μm.

According to the second aspect of the present invention, the conventional groove processing is not required by using the transition metal and the rare-earth element metal as powder materials to manufacture the electrode, thereby improving the workability and strength, and improving the electrode body. Can also be made larger. Therefore, the size of the immobilization container after the radioactive gas immobilization process can be increased, and in particular, the volume reduction effect of storage can be effectively increased.

The injection amount of the radioactive gas is 10-15.
If the content exceeds vol%, the strength is reduced. According to the invention of claim 4, by setting the rare earth metal particles to 10 to 50% by volume, the injection amount of the radioactive gas can be increased, and the electrode body having excellent strength can be obtained.

If the composite metal constituting the sputter electrode is less than 90% of the theoretical density, the stability of sputtering is poor. According to the fifth aspect of the present invention, by setting the composite metal constituting the sputter electrode to at least 90% of the theoretical density, the stability of sputtering is improved.

Further, in manufacturing the electrode body of the sputter electrode, the densification after mixing the transition metal powder and the rare earth metal powder and putting them in a mold is affected by the heating temperature and the pressure. For example, a hard and brittle reaction layer is generated at the interface between the mother phase and the particles, which may reduce the strength of the electrode body of the sputter electrode. According to the invention of claim 5,
100-200 at the same time heating at 400-1000 ° C
By applying a pressure of 0 kgf / cm ² , it is possible to suppress the formation of a hard and brittle reaction layer generated at the interface between the mother phase and the particles. Since the composite metal layer can be densified, stable sputtering can be performed.

Further, according to the present invention, the surface other than the surface of the sputter electrode facing the ion-implanted electrode is held by a metal having a higher sputtering rate threshold than that of the mother phase. The amount of sputtered metal that jumps out from other sources is reduced, and it is possible to easily prevent adhesion to the insulating material provided in the fixed container.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a radioactive gas fixing apparatus according to the present invention will be described below with reference to the drawings.

Example 1 (FIGS. 1 to 3) FIG. 1 is a schematic configuration of a sputter electrode, FIG. 2 is a schematic view showing a cross section of an electrode main body peripheral wall structure of the sputter electrode, and FIG. FIG. In addition,
Since the overall configuration of the apparatus is substantially the same as that shown in FIG. 6, its description is omitted.

In this embodiment, as shown in FIG. 1, the electrode body 20a of the sputter electrode 20 is composed of a cylindrical composite metal layer 21 having axially open ends, and an inner layer 2 provided inside the composite metal layer 21.
2, a bottom wall 23 formed integrally with the inner layer 22, and an electrode lid 24 welded to the upper end opening of the inner layer 22. Note that the inner layer 22 is made of stainless steel or the like. Further, a double pipe 25 for circulating cooling water is inserted into the electrode body 20 through the electrode lid 24.

In this case, the composite metal layer 21 on the peripheral wall of the electrode body 20a is formed by mixing a transition metal powder and a rare earth metal powder and molding the mixture. The structure is made compact by compression under pressure. Nickel (Ni), copper (Cu), or the like was used as the transition metal powder. As the rare earth metal, yttrium (Y), lanthanum (La), zirconium (Zr) and the like were used.

The particle size of the rare earth metal powder used in this embodiment is 1000 μm, and the amount of the rare earth metal powder mixed into the transition metal is 30% by volume. This is heated at 600 ° C. and 1000 kgf /
By applying a pressure of ² cm ² , the rare earth metal particles were dispersed. As a result, the uniformization can be easily performed, the theoretical density becomes 90% or more, and as shown schematically in FIG. 2, the particles 2 of the rare earth element metal are contained in the matrix 21a made of the transition metal.
1b was uniformly dispersed.

When the radioactive gas was immobilized using the sputter electrode 20 of the present embodiment configured as described above (see FIG. 6), the composite metal layer 21 was formed without the rare-earth metal dropping on the way. Sputtering was completed until the end. When the composite metal layer 21 has a large particle diameter,
As in the case of the conventional structure of the sputtered electrode, the solidified metal produced by sputtering is likely to be non-uniform and the strength is reduced. However, according to the present embodiment, the uniformization can be easily performed and the theoretical density is 90% or more. The sputtering was stabilized, and the solidified body could be homogenized.

Further, in this embodiment, the portion of the electrode body 20 which is in contact with the cooling path is the inner layer 22 made of a metal different from the composite metal layer 21, so that there is no leakage of cooling water and the electrode is used as a target. Was safe and effective. When the sputtered electrode of this example was used, the ratio of the rare earth metal was higher than that of the solidified body having the conventional structure, and sputtering could be performed efficiently.

Furthermore, when the sputter electrode is formed by the composite metal layer 21 made of the transition metal powder and the rare earth metal powder, the conventionally required high-precision deep groove processing is unnecessary, and the sputter efficiency and the storage efficiency are improved. In addition to the increase in the rare earth metal concentration and the size increase, the production cost was significantly reduced.

Further, after the transition metal powder and the rare earth metal powder are mixed, sintering at a low temperature facilitates the processing, thereby significantly reducing breakage in the processing step and reducing the processing cost.

FIG. 3 shows the processing time of the sputter electrode body having the structure according to the present embodiment in comparison with the conventional structure. In the conventional structure, as shown in FIG. 12, a groove is formed in a metal ingot, and a rare earth element metal is sandwiched and mixed, followed by press working.
Finishing was performed, and more time was required for metals with different workability. It can be seen that the processing capacity was remarkably improved to 79 hours in the conventional structure, but to 12 hours in the structure of the present embodiment.

Example 2 (FIGS. 4 and 5) FIG. 4 is a schematic configuration of a sputter electrode, and FIG. 5 is a graph showing the effect (strength) of the present example.

The difference between the sputter electrode 20 of the present embodiment and the first embodiment is that flange portions 24a are integrally formed at both axial ends of the inner layer 24 constituting the sputter electrode body 20a.
The point is that the metal layer holds not only the inner surface of the composite metal layer 21 but also both ends in the axial direction. Examples of the material of the metal layer include transition metals such as nickel (Ni) and copper (Cu) having a higher threshold for sputtering than the composite metal layer 21 formed of a transition metal and a rare earth element metal, and stainless steel. It is formed integrally with the composite metal layer 21 by pressure sintering using steel.

Since other points are substantially the same as those in the first embodiment, the same reference numerals as those in FIG. 1 denote corresponding parts in the drawing, and a description thereof will be omitted.

According to this embodiment, the metal layer for holding the composite metal is made of a metal having a higher sputtering threshold value than the constituent material of the composite metal layer, so that sputtered particles adhering to the insulator can be reduced. This makes it possible to operate for a long time, improve the strength, and cope with an increase in the size of the sputter electrode 20.

FIG. 5 shows the results of a tensile test of this embodiment using stainless steel in comparison with a conventional structure. In the conventional structure, deep grooves cause stress concentration,
Since the strength of the transition metal itself is very low, it is difficult to maintain the dead weight of the electrode at a high temperature, and thus it is difficult to increase the size of the sputter electrode. Since the layer is made of stainless steel which is also excellent in strength, the strength is increased and the electrode can be made larger.

Experimental Example 1 (FIG. 6) FIG. 6 is a table showing the relationship between the combination of the transition metal and the rare earth element constituting the mother phase of the sputter electrode applied in the present invention and the injection efficiency. The left column shows a combination of a transition metal and a rare earth element (transition metal-rare earth element). The right column shows double circles, single circles, and triangles in order from the best.

As shown in the figure, the combination of nickel and yttrium (Ni-Y) had the highest injection efficiency, and the combination of copper and yttrium (Cu-Y) was also good. Next, a combination of nickel and lanthanum (Ni
-La), a combination of copper and zirconium (Cu-Z)
r).

Experimental Example 2 (FIG. 7) FIG. 7 is a table showing the relationship between the particle size of the rare earth element powder applied in the present invention and the workability, sputtering stability, and film forming uniformity. Good ones are indicated by circles, slightly good ones are indicated by triangles, and poor ones are indicated by crosses.

When the particle size was 80 μm, workability, sputtering stability, and film uniformity were poor. Especially in the workability, micro cracks occur during processing,
Difficulties in temperature control. Particle size of 1000 to 20
Almost good results were obtained in the case of 00 μm. When the particle diameter was 3000 μm, the particles dropped during processing.

Experimental Example 3 (FIG. 8) FIG. 8 is a table showing the relationship between the ratio of the rare earth element powder to the transition metal applied in the present invention and the workability and sputtering. Good ones are indicated by circles, slightly good ones are indicated by triangles, and poor ones are indicated by crosses.

When the ratio was 5%, sputtering was somewhat good, but workability was poor. 10-50%
In the case of, almost good results were obtained in both workability and sputtering. In the case of 60%, sputtering was good but workability was poor.

Experimental Example 4 (FIG. 9) FIG. 9 is a table showing the relationship between the density of the composite metal forming the sputter electrode and the sputtering stability. A stable one is a circle, a slightly stable one is a triangle, and an unstable one is ×.
This is indicated by a mark.

When the metal density was 85%, the sputtering was unstable, slightly stable at 90%, and stable at 95% and 99.9%.

Experimental Example 5 (FIG. 10) FIG. 10 is a distribution diagram showing the quality of workability with respect to the heating temperature and pressure in the densification processing of the sputtered electrode. Good workability is indicated by circles, slightly good ones are indicated by triangles, and poor ones are indicated by crosses.

As can be seen from the figure, the range in which the workability is good is that the densification of the sputter electrode is performed at a heating temperature of 400 to 1000 ° C. and a pressure of
It can be seen that the region is 0 to 2000 kgf / cm ² . At a pressure of kgf / cm ² or less, the material was melted without densification, and an intermetallic compound was generated, resulting in poor workability.

[0056]

As described above, according to the present invention, a radioactive gas is fixed by forming a sputter electrode from a composite metal in which rare earth element particles are densely dispersed in a matrix composed of a transition metal. A large volume reduction effect can be stored and stored in the handling of the fixed container later, and the rare-earth element powder dispersed in the transition metal has a particle size of 100 to 2000 μm, so that the rare-earth element can be removed. It can be uniformly dispersed in the mother phase and can increase the strength. In addition, the main constituent members of the apparatus can be manufactured efficiently and economically, and the radioactive gas fixing process can be performed stably. This has a great effect on the radioactive gas fixing process.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of a sputter electrode according to a first embodiment of the present invention.

FIG. 2 is a partially enlarged schematic sectional view of FIG.

FIG. 3 is a graph showing the effect of the embodiment.

FIG. 4 is a cross-sectional view illustrating a schematic configuration of a sputter electrode according to the first embodiment of the present invention.

FIG. 5 is a graph showing the effect of the embodiment.

FIG. 6 is a table showing Experimental Example 1 and shows a relationship between a combination of a transition metal and a rare earth element constituting a mother phase of a sputter electrode and an injection efficiency.

FIG. 7 is a table showing Experimental Example 2 and shows the relationship between the particle diameter of rare earth element powder, workability, sputtering stability, and film forming uniformity.

FIG. 8 is a table showing Experimental Example 3 and shows the relationship between the ratio of rare earth element powder to transition metal, workability, and sputtering.

FIG. 9 is a table showing Experimental Example 4, and shows the relationship between the density of the composite metal forming the sputter electrode and the sputtering stability.

FIG. 10 is a distribution diagram showing Experimental Example 5, and shows the quality of workability with respect to heating temperature and pressure in densification processing of a sputter electrode.

FIG. 11 is an overall view showing an apparatus for immobilizing radioactive gas.

FIG. 12 is a sectional view showing a schematic configuration of a sputter electrode in a conventional example.

[Explanation of symbols]

 Reference Signs List 20 sputter electrode 20a sputter electrode main body 21 composite metal layer 21a mother phase composed of transition metal 21b rare earth element particles

Continuation of front page (56) References JP-A-4-72599 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G21F 9/02

Claims (6)

(57) [Claims] A sputter electrode is disposed on an inner surface of a container-like ion implantation electrode for introducing a radioactive gas, and a sputter electrode generated from the sputter electrode is formed on the inner surface of the ion implantation electrode by a sputtering effect due to a glow discharge between the two electrodes. In a radioactive gas immobilization treatment apparatus for implanting and accumulating a radioactive gas ion in the sputtered metal accumulation layer while implanting and forming a metal accumulation layer, the sputtered electrode is formed by adding a rare earth element to a transition metal matrix. An apparatus for immobilizing a radioactive gas, comprising: a composite metal in which element particles are densely dispersed; and a particle diameter of the rare earth element powder is 100 to 2000 μm. 2. The transition metal constituting the mother phase of the sputter electrode is made of a powder of nickel, copper or another transition metal, and the particles of the rare earth element are powders of yttrium, lanthanum, zirconium or other rare earth metal. The radioactive gas immobilization treatment apparatus according to claim 1, wherein the radioactive gas is used as a material. 3. The radioactive gas immobilization apparatus according to claim 1, wherein the rare earth metal powder is dispersed in the transition metal at a ratio of 10 to 50% by volume. 4. The radioactive gas immobilization treatment apparatus according to claim 1, wherein the composite metal constituting the sputter electrode is 90% or more of the theoretical density. 5. Densification of a sputter electrode is performed at a heating temperature of 40.
0 to 1000 ° C, pressure 100 to 2000 kgf / cm ²
The radioactive gas immobilization treatment apparatus according to any one of claims 1 to 4, wherein the treatment is performed by: 6. The sputter electrode has a cylindrical shape, and its inside and both ends in the axial direction are held by a metal layer having a higher sputtering threshold than a transition metal. The radioactive gas immobilization apparatus according to any one of the above.