JPH0679078B2 - How to contain a toxic substance container - Google Patents

Description

The present invention relates to a method for containing a toxic substance container. Toxic substances, especially radioactive waste, are often stored in sealed metal barrels for storage. A problem with such a torso is whether it remains fully robust against environmental degradation, ie its useful life.

According to the conventional method, the metal cylinder containing the radioactive waste is contained in a container such as steel, concrete or asbestos cement, and the remaining gap is filled with concrete.

This method can only be applied to wastes with relatively low radioactivity when the heat generated is negligible.

In the case of highly radioactive waste, such as the fission products in glass containers, it is not possible to contain the metal shell containing such substances even after several years due to heat radiation. Is.

An object of the present invention is to provide a method for containing a metal cylinder that can withstand deterioration of the environment in a sealed state of radioactive waste for a long period of time.

A feature of the present invention is that the metal cylinder is surrounded by a fine-particle ceramic paste or an unfired ceramic paste obtained by pressure-molding a fine-grain ceramic paste and fired.

Another feature of the present invention is that the unfired ceramic paste is made of porcelain raw material, clay or stoneware raw material.

In the present invention, a member corresponding to the change in the dimensions of the container and the unfired ceramic paste is also used.

The container in this invention includes a single metal shell containing radioactive waste or a bonded metal shell such as that surrounded by a fired ceramic shell.

In this invention, there are two different cases. In the first case, it is necessary to use a container having a coefficient of expansion different from that of the unfired ceramic paste, and to use a member corresponding to the dimensional change between the container and the unfired ceramic paste, and in the second case. The container and the unfired ceramic paste have similar coefficients of expansion, and it is not necessary to use a member that responds to dimensional changes.

In the method of the present invention, a mold 1 in which a piston 2 slides as shown in FIG. 1 is used.

A layer of fine ceramic paste, which is a raw material of the unfired ceramic paste, is placed on the bottom of the molding die 1, and the pinst 2 is pressed to form the unfired ceramic bed 4.

The container 3 is placed on the bed 4, and the whole is covered with the fine ceramic paste.

Then, the piston 2 descends and pressurizes the whole. The pressure applied by the piston 2 is 10 to 60 MPa, preferably 35 MPa.

If pressed with a pressure of 10 MPa or less, the unfired ceramic paste will not become solid, and if pressed with a pressure of 60 MPa or more, the wall surface may crack unless it is thickened, which increases the price and weight. Will increase.

A molded product is taken out by raising the piston 2 and removing the bottom of the mold. Although FIG. 1 does not show the mold with the bottom removed, the principle is well known to those skilled in the art. It can also be pressed at a pressure of 10 to 60 MPa, preferably 40 MPa, depending on the weight.

The moldings are air-dried or oven-dried and then placed entirely in a kiln and fired at the temperature required to turn the unfired ceramic paste into a fired product (eg 1150 ° C for stoneware, 1250-1300 ° C for porcelain). To do. The size of the container determines the temperature rise.

A problem that arises during the firing cycle is the different expansion of the container and the ceramic.

Usually the container is made of steel. The enclosure has a diameter expansion of 1.8% between ambient temperature and 1100 ° C. and the fired ceramic has an expansion of 0.45% under the same conditions.

Moreover, the green ceramic paste shrinks about 5% in the first firing operation.

To overcome these diameter changes, the method of the present invention places a member around the enclosure which is capable of compensating for the diameter changes linked to expansion and contraction that occur during the firing cycle.

A container with a diameter of 400 mm at 20 ° C has a diameter of 408 mm at 1100 ° C. Accompanying this, the ceramic shrinks about 20 mm.

In order to solve the problem of this difference in diameter, according to the invention, it decomposes completely and partly during firing, or decomposes by degassing, for example, fusible or thermal or mechanical. A member whose thickness can be changed by force is used.

In this way, at the start of the container, the container does not show a high temperature due to radioactivity and the member is stable at the atmospheric temperature, but it is suitable that the member disappears when heated. Such components consist of wax, paraffin or plastics such as polyethylene (or other olefins), or polyvinyl alcohol.

FIG. 2 shows the container 5 surrounded by the paraffin layer 6.

The tests carried out by the Applicant disappear without leaving traces, transform into a gas when the temperature rises and diffuse through the ceramic wall before the porosity of the green ceramic paste is completely closed by firing. In this way a space is created and the container expands during the firing without applying pressure to the ceramic paste.

Another alternative is to use an elastic material, which may be a combination of felt, cloth or string with a number of fibers. FIG. 3 shows the felt surrounding the cylindrical container.

The felt or cloth used in this method is composed of silica, carbon or silica aluminum. The other felt consists of an organic felt that disappears on heating in the same manner as described above.

To enclose the cylindrical container 5, the rectangular felt sheet with a thickness of 30 mm is used. The dimensions of this sheet are the same in height and perimeter as that of the cylindrical container. FIG. 4 shows a state in which the ends of the felt 7 are joined along the line 8 and the felt 7 surrounds the cylindrical container 5. The whole is integrally connected by a tightening string 9.
Two caps of the same diameter as the cylindrical container with the diameter increased by 60 mm are made of felt and are attached to the upper and lower ends of the cylindrical container so as to cover them.

In this way, a container whose entire surface is surrounded by felt,
It is placed on a bed of finely divided ceramic paste and encapsulated as described above. When high density silica felt is used, its thickness decreases from 30 mm to 20 mm after pressing. This thickness will compensate for the dimensional changes that occur during firing.

After cooling, the felt partially recovers its thickness and the metal cylinder fills the gap between it and the fired ceramic.

If the container shape is more complex, a thick cloth or felt is used to attach to the outer surface of the container.

Also, the cord or the string can be tightly wound around the outer circumference of the container. Depending on the diameter of the cord, the winding layer must be a plurality of layers wound tightly. The moldings made of cloth, felt or cord are sewn or glued to each other in order to simplify the mounting work.

Suitable green ceramic pastes consist of porcelain raw materials, mullite and stoneware raw materials.

The porcelain raw material 4 is made of kaolin, feldspar, and sand. Stone tools are made of sand, clay and feldspar. These paste mixtures are already known.

The heating cycle remains to be determined by the ceramics vendor.

The following examples are intended to illustrate, but are not limited to, the method of containment of containers with different ceramic geometries in a firing cycle tailored for each test.

In some cases it is advantageous to provide containment within an already fired ceramic shell. This is because the metal shell is pre-packaged in the ceramic shell to prevent the diffusion of radioactivity leaked to the surface of the metal shell, and similarly the ceramic shell also prevents the diffusion of radioactive material when the metal shell is damaged. .

For the method of containment as described above, a ceramic shell having a cylindrical body with two hemispherical ends is used, which ends better distribute the forces generated during the pressing operation.

FIG. 5 shows a schilling 1 fitted with two hemispherical ends 11, 12.
The shell formed by 0 is shown. The joining of the parts is achieved by the engagement of notches 13 and 14 provided in the hemispherical end 15 and the cylindrical body 16, as shown in FIG.

Another form of shell is shown in FIG. 6, where the ends 17, 18 consist of hollow hemispherical ends, which are joined to the cylindrical body, and the joining surface between the ends is a horizontal plane. ing.

FIG. 7 shows a shell consisting of two parts joined in a longitudinal plane.

The shell-forming material consists of stone or porcelain, especially hard mullite.

Similar materials are used to make shells. However, without limitation, two different materials are used when the difference in expansion coefficient is small. In this case, it is advantageous for the material with the highest expansion coefficient to be placed on the outside.

Such shells are easily obtained by well known heating and firing techniques.

According to the present invention, a metal barrel 23 is placed within a fired ceramic shell 24, as shown in FIG. The gap between the metal shell and the shell is partly or wholly filled with mineral powder 22, said powder having a diameter of 0.5 to 10 mm, preferably 3 mm.
To 5 mm particles. Mineral powders that can withstand heat in a heating cycle, such as corundum powder, are suitable.

Various uranium oxides (especially UO ₂ or U ₃ O ₃ )
The use of powder is advantageous as it forms a containment vessel with the metal barrel 23, the fired ceramic shell 24 and the mineral powder 22.

If necessary, it is surrounded by a material that responds to dimensional changes as described above, and an unfired ceramic paste is molded around it, the whole finally undergoing a firing operation, resulting in an integral molding.

According to two other embodiments of the present invention, an unfired ceramic paste enclosure is used in which a container is placed.

According to the first embodiment, as shown in FIGS. 11 to 15, the fine-grained ceramic paste is placed on the bottom of the molding die 25 as shown in FIG. 11 and is not fired as shown in FIG. It is pressed with Pinston to get a bed of ceramic paste 28.

The piston comprises a central part 27 and a peripheral part 26.
As shown in FIG. 13, the central portion 27 is held in place and the peripheral portion 26 is lifted to form an annular gap 29 between the central portion 27 and the inner wall of the mold. And the gap 29
Is filled with fine-grained ceramic paste and then pressed at the peripheral portion 26 as shown in FIG. 14, so that the height of the unfired ceramic paste becomes substantially equal to the height of the container. 15th
The figure shows the molding 30 obtained as a result of this operation.

The container is then placed inside the molding 30. Then, when it is necessary to cope with the dimensional change between the container and the paste, either a member which disappears upon heating or has elastic characteristics is placed between the container and the paste.

In this embodiment, the technician can perform two operations. The first operation is shown in FIGS. 16 to 21, and the inner wall of the green ceramic paste molding 30 is shown in FIG. As shown, a member 31 selected to accommodate the dimensional change is inserted. A container 32 is placed in the remaining space as shown in FIG. 17, a layer 33 of unfired ceramic paste is placed on the container as shown in FIG. Has been extended to. As shown in FIG. 19, a layer 34 of fine-grained ceramic paste is laid down and pressed by a piston as shown in FIG. 20 to obtain the molding 35 shown in FIG. The pressure applied for this may be 60 MPa or more, but it is preferably 35 to 40 MPa. The container 32 is surrounded by the unfired ceramic paste with a substantially uniform thickness. The molded product 35 is molded, dried, and fired to obtain a ceramic integrated block.

Instead of placing the member 31 corresponding to the dimensional change so as to cover the inner wall of the pressure-formed product 30 of the unfired ceramic paste,
It may be directly formed on the container 32 by coating or the like. However, it is not necessary to place the layer 33 of said member on top of the container.

According to the second embodiment shown in FIGS. 22 to 28, a large amount of finely divided ceramic paste is pressed into the molding die with a proper thickness, and a hole large enough to place the container 32 and the molding 31 is formed. It is provided and the height of this hole is approximately equal to the height of the container. A top layer of finely divided ceramic paste is laid down and pressed, and the container is surrounded by a layer of unfired paste of the same thickness that is present all around its circumference. The molding is then demolded, dried and fired to obtain a seal.

The following examples are intended to facilitate understanding of the invention and are not intended to be limiting.

Example 1 A cylindrical steel cylinder has a diameter of 50 mm and a height of 75 mm, and solid waste stored therein (powder, metal chips, glass, etc.)
Is manually coated with 4 mm thick paraffin.

The fine mullite ceramic paste is placed in a mold with an inner diameter of 150 mm and a height of 200 mm and pressed. The product used in this example is that produced under "Limousine Kaolin and Ceramic Paste" under 42555.

The same fine-grained ceramic paste is filled in the remaining gaps in which the steel cylinder is housed.

The pressurizing piston presses at a pressure of 35 MPa. The pressure at that time was increased from 0MPa to 5MPa in 5 minutes, maintained for 5 minutes, then decreased to 0MPa, and again 10 minutes in 5 minutes.
It is increased to MPa and held for 5 minutes, then reduced to 0 MPa, further increased from 0 MPa to 35 MPa for 10 minutes and held for 30 minutes, and then reduced to 0 MPa.

The steel barrel is then surrounded by a layer of pressed green ceramic paste to a thickness of 50 mm.

The product thus obtained is dried and then to a certain degree over the next two days from 25 ° C to 300 ° C, then from 800 ° C to 1000 ° C per day, and then to 1000 ° C per day.
From 1100 ° C to 1220 ° C on 2.5 days then heated to 1220 ° C to 25 ° C on 2.5 days
Was lowered to.

The integrally fired block is then removed from the furnace.

The finely divided ceramic paste used in this method contains 3-5% by weight of water. Fine-grained ceramic paste containing 3% or less of water may disintegrate when depressurized as a block under pressure, and fine-grained ceramic paste containing 5% or more of moisture may not bond well after pressing. There is a fear that the block will collapse again.

The maximum and minimum amount of moisture is related to the properties of the fine ceramic paste paste.

Example 2 A cylindrical steel cylinder having a diameter of 50 mm and a height of 75 mm as shown in FIG. 6 was surrounded, and the ends were joined as shown in FIG.

These three members 17, 18 and 19 were formed by a stoneware raw material obtained by grinding and mixing in an arson wear jar.

White calcined clay 45% Kaolin 15% Fenten blow sand 20% Feldspar 20% Description of molding and firing work is omitted. Firing temperature is 1150 ℃
This was maintained for 8 hours.

The final member that makes up the shell has a cylinder outer diameter of 100 mm, a height of 75 mm, and a wall thickness of 20 mm.

A steel barrel was placed on the bottom of the hemisphere and 55 cm ² of corundum powder (1 mm particles) was inserted into the shell before the lid was placed.

The container was placed on a pressure layer of fine ceramic paste (containing 3.8% by weight of water) having an inner diameter of 200 mm and a height of 300 mm. The mold was filled with a fine-grained ceramic paste having a structure similar to that used for the three members of the shell, and the shell was arranged so as to be centered in the height direction and the radial direction in the mold.

A sufficiently large force was applied to the pinst so that a pressure of 35 MPa was generated in the mold. 0 for 5 minutes at this stage
To raise the pressure from 5 MPa to 5 MPa and stop it for 5 minutes
Decrease to 0MPa, then increase from 0 to 10MPa in 5 minutes and hold it for 5 minutes, then decrease to 0MPa, then increase from 0 to 10MPa in 5 minutes, hold it for 5 minutes, then to 0MPa Decrease, then 0 to 35 in 10 minutes
Increase to MPa, maintain at 35 MPa for 30 minutes, then decrease to 0 MPa. In this way the amount of air contained in the substance is minimized. The demolded parts are dried in an oven for 24 hours and then placed in an electric oven.

The curve shown in FIG. 10 shows the temperature program as a function of time. It takes 7 days to rise to 1150 ° C., then leveles for 8 hours, and drops to atmospheric temperature after half a day.

When the results were examined with a binocular lens, it was found that a homogeneous cylinder having no holes or cracks was obtained.

The inside can be observed by the cutting operation, and the metal container is surrounded and housed by coarse particles. The ceramic paste that forms the ceramic solid tightly surrounds the shell and leaves no trace of separation from each other on either the inner surface of the solid or the outer surface of the shell.

Example 3 The experiment covers a glass filled stainless steel container. Its diameter is 300 mm and its height is 1400 mm. A frit patch is provided at the inlet to allow air in and out in order to avoid over-pressurization of the internal pressure during the firing operation.

The first step consists of preparing the two shell members shown in FIG. 8 formed from No. 42555 fine grain ceramic paste sold as "Limousine Kaolin and Ceramic Paste". Such unfired ceramic paste becomes mullite when fired at 1260 ° C.

After firing, the outer diameter of the cylinder is 610 mm and the height is 1200 m.
m, the wall thickness is 100 mm.

It is recommended that the above-mentioned two-shell member is formed by applying a pressure of 40 MPa by gravity. The pressure is 1 to 60
MPa.

The cylindrical mold used has an inner diameter of 850 mm and is equipped with a hydraulically actuated piston, the stroke of which is a minimum of 2400 mm.

Corundum powder of about 3 mm particles in the lower half of the shell is poured onto a layer of No. 42555 fine-grained ceramic paste, which is placed in the bottom of the mold and pressed, and then the container is introduced. Free space is filled with corundum powder before the upper half of the shell is placed. A hole is provided in the upper shell for pouring corundum powder, the barrel is pushed into that position, and the hole is plugged.

The gap remaining around the shell in the mold is filled with No. 42555 fine-grained ceramic paste, which has an overall thickness of 120 mm, which is sufficient to avoid the occurrence of weak spots.

The pressing operation is performed in the same manner as in the above-described embodiment in order to degas the unfired ceramic paste.

The final pressure is 35 MPa, but it may be 20 to 60 MPa.

The demolded green compact is dried in the atmosphere for 7 days, then dried in a drying oven for 2 days, and then fed into an electric tunnel kiln. The heating program is as follows: 100 ° C per day to 600 ° C, 50 ° C per day to 600 ° C to 900 ° C, 25 ° C per day to 90 ° C.
The temperature rises from 0 ° C to 1200 ° C, is maintained at 1200 ° C for 2 days, and then rises to 1260 ° C at a rate of 25 ° C per day. The temperature is maintained at 1260 ° C for 4 days, and then the temperature is lowered to atmospheric temperature at a rate of 100 ° C per day. Thus, the total cycle time is about 40 days.

It is easy to see that it is necessary to provide an outlet for the air contained in the container during heating, and the internal pressure will exceed 0.5 MPa, which will deform the container.

Although described centering around covering and protecting the metal shell containing the glass, the method is also applicable to other types of waste, the firing cycle of which is the needless pressurization of the enclosure under high heat. Does not cause decomposition by.

Also, at the temperature at which the coated ceramic paste is porous, degassing is performed outside the container,
Virtually no problem.

This invention made it possible to contain toxic waste such as nuclear waste in a very stable manner.

The above was done with respect to a shell consisting of a cylinder which is symmetrical about an axis. However, the invention is applicable to other types of enclosures or shells.

Further, in the present invention, only the metal cylinder has been described, but the present invention is also applicable to other materials in which the material forming the metal cylinder has a coefficient of expansion different from that of ceramic.

[Brief description of drawings]

FIG. 1 is a vertical sectional front view of an apparatus for carrying out the method according to the present invention, FIG. 2 is a front view showing a paraffin-enclosed container, and FIG. 3 is a state in which felt is wrapped around the container. FIG. 4 is a perspective view showing a state in which the felt of FIG. 3 is wound around a container, FIG. 5 is an exploded perspective view of a shell made of three members, and FIG. 6 is a perspective view of a shell made of two members. Exploded slope view,
FIG. 7 is a perspective view of a half of the shell which is disassembled along the longitudinal plane, and FIG. 8 is a partial perspective view showing a joint portion of two members of the shell,
FIG. 9 is a vertical sectional front view showing a state in which the metal cylinder is placed inside the shell and is encapsulated by the unfired ceramic paste,
FIG. 10 is a table showing a heating cycle for firing a combined product of a container, a member corresponding to a change in size, and an unfired ceramic paste, and FIGS. 11 to 21 show the first embodiment of the present invention.
FIGS. 22 to 29 are explanatory views showing the process sequence of the embodiment, and FIGS. 22 to 29 are explanatory diagrams showing the process sequence of the second embodiment of the present invention. 1 ... Mold, 2 ... Piston 3,5,32 ... Container, 4 ... Bed 6 ... Paraffin, 7 ... Felt 22 ... Powder, 23 ... Metal shell 24 ... Shell, 26, 27 …… Piston 28 …… Unfired ceramic paste 29 …… Annular gap, 30 …… Molded product

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Francis Roman France, 28210 Nogien Le Roix, Marmiyuran Cyodon, Aldora Laforet 9 (56) Reference JP-A-57-118200 (JP, A) JP A 59-116100 (JP, A)

Claims (12)

[Claims] 1. A ceramic solid which surrounds the entire surface of a container containing a toxic substance with a fine-grained ceramic paste, pressurizes it to form an unfired ceramic paste, and then is wholly dried, heated and sealed. A method for containing a toxic substance container, which comprises forming a container. 2. A member corresponding to a change in dimension between the unfired ceramic paste and the container when the expansion coefficient of the container is different from that of the unfired ceramic paste. The method for containing a toxic substance container according to item 1. 3. A container, which is pre-enclosed with a member corresponding to a change in size, is placed on the base of the unfired ceramic paste installed at the bottom of the mold, and fine particles are formed in the gap between the mold and the container. The method for containing a toxic substance container according to claim 1 or 2, wherein the ceramic paste is filled and the whole is pressurized. 4. A container, which is pre-enclosed with a member corresponding to a change in size, is placed in a housing of unfired ceramic paste, and a layer of fine ceramic paste is placed on the container and the upper surface of the housing, The method for containing a toxic substance container according to claim 1, wherein the container is pressurized. 5. A container is placed in a housing of unfired ceramic paste, a member corresponding to a dimensional change is installed in a gap between the housing and the container, and a layer of the member is placed on an upper surface of the container. The method for containing a toxic substance container according to claim 1 or 2, wherein the member is surrounded by a fine ceramic paste layer and the whole is pressurized. 6. The poisonous substance according to any one of claims 1 to 5, wherein the fine-grained ceramic paste and the unfired ceramic paste are configured to be porcelain after firing, particularly porcelain having good mechanical strength. How to contain a substance container. 7. A method for containing a toxic substance container according to any one of claims 1 to 5, wherein the fine-grain ceramic paste and the unfired ceramic paste are stoneware (stoneware) after firing. . 8. A member corresponding to a change in dimension is wax,
The method for containing a toxic substance container according to any one of claims 2 to 7, which is made of paraffin, plastic, polyolefin, or the like that disappears by heating. 9. The method according to any one of claims 2 to 7, wherein the member corresponding to the change in dimensions has elastic properties and is made of a felt or cloth made of a fibrous material of special silica, carbon or glass. How to Contain Toxic Substance Containers. 10. A method for containing a toxic substance container according to claim 3, wherein a pressure of 10 to 60 MPa, preferably 35 to 45 MPa is applied by a piston inserted into the mold. 11. Gravity of 10 to 60 MPa, preferably 3
The method for containing a toxic substance container according to claim 3, wherein a pressure of 5 to 45 MPa is applied. 12. A container for a toxic substance comprises a fired ceramic shell surrounding a metal cylinder filled with a toxic substance, and a gap between the metal cylinder and the shell is partially or entirely formed of corundum powder or uranium oxide powder. A method for containing a toxic substance container according to claim 1, wherein the powder is filled with a mineral powder such as that described in (1), and the particle size of the powder is 0.5 to 10 mm, preferably 3 to 5 mm.