JPH0636073B2 - Method for melting treatment of a treatment object containing zirconium or zirconium alloy - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for melt-processing an object to be processed containing zirconium or a zirconium alloy in a metal container.

(Prior Art) Typical products made of zirconium simple substance and zirconium alloy used in the field of nuclear power are as follows.

(A) A metal tube for filling uranium dioxide fuel, which is a nuclear fuel material, in a pellet form, that is, a zircaloy metal clad tube made of an alloy of zirconium and tin, (B) A zircaloy metal clad tube filled with fuel pellets for a nuclear reactor. When loading, prismatic channel box made of Zircaloy metal to facilitate contact with water in the furnace or loading work into the furnace, (C) Shearing process when reprocessing spent fuel The column tanks used to dissolve the fuel substance from the short nuclear fuel cladding tube using concentrated nitric acid and hydrofluoric acid mixture, that is, a dissolution reaction tank made of zirconium alone or an alloy of zirconium and tantalum, and Concentration tanks for these solutions, as well as piping parts used in these devices, and products of these zirconium or zircaloy metals are Occur as wastes. The channel box was removed when transporting the spent fuel to the reprocessing plant,
At this time, it is generated as waste.

At the reprocessing plant, a short piece of nuclear fuel clad tube that was sheared from concentrated nitric acid solution in a hydrofluoric acid mixture was immersed, and when the spent nuclear fuel material inside was dissolved, a short piece of clad tube (zircaloyhal) was produced as a residue. Occur. Further, the dissolution reaction tank, the concentration tank, the piping, etc. are generated when they are dismantled for the reason of life etc.

That is, zirconium alone and zirconium alloys have a high melting point of 1800 ° C. or higher and are more excellent in corrosion resistance than other metals, so they are used under the most severe conditions. As a result, the substance itself is highly activated by neutron irradiation, and moreover, transuranium elements such as plutonium dioxide and fission products such as cesium are attached as undissolved residues. As a result, special handling and strict storage and management in the event of disturbance are required.

With respect to these zirconium-based wastes, it has been attempted to develop various treatment methods for the purpose of volume reduction and stabilization.

The following items are factors that make this process difficult.

(1) Due to high activation and deposition of transuranic elements, special handling technology by remote control is required in an environment where airtightness is required.

(2) The melting point is high (1800 ° C. or higher), (3) Oxygen or hydrogen gas is absorbed at a temperature of 500 ° C. or higher, or the temperature is 1400 ° C. or higher with a crucible of an oxide such as Al ₂ O _3. When dissolved, it has a strong chemical activation effect such as reduction of the crucible.

Based on these factors, there is a method of using hot isostatic pressure (HIP) as a method of performing recent volume reduction and stabilization treatment. This method is a method in which a three-dimensional hydrostatic pressure is applied at a high temperature of 1000 ° C. or higher to a pressure medium mainly composed of an inert gas such as argon gas, isotropic compression is performed, and diffusion bonding is performed. This method can be said to be good for small-sized waste such as hulls, but large waste such as channel boxes needs to be cut into pieces, and vacuum degassing is performed after filling the container. There are conditions such as necessity, and the processing steps are complicated.

Further, the following is known as another treatment method for zircaloyhal. That is, (1) RECENTS DEVELOPPEMENTS DANS LA FUSION PA
R INDUCTION ENCREUSET FROID J REBOUX ETAL CEA,
MARCOULE, FRANCE (1984) (2) CONDIONNEMENT ET DICONTAMINATION DESDECHETS
DE GAINE D'ELEMENTS COMBUSTIBLES NUCLEAIRES P
AR FUSION JJFRANCILLON ETALCEA, MARCOULE, FRA
NCE (1982) In the method of (1) above, zircaloy hull itself is arranged in the periphery so that a prismatic water-cooled mold made of water-cooled copper is formed in a cylindrical space, and from the outside of this cylindrical space, a cylindrical space is formed. Apply a high frequency by winding a high frequency coil to surround the
Zircaloyhal is supplied to the cylindrical space and melted.

In this method, since a high frequency is applied to the supplied hull, the hull having a high melting point of 1860 ° C. can be melted.
The melted hull is withdrawn from the lower part of the cylindrical space while being cooled. This method can directly melt the hull with a high melting point, and can process the shape and size of the supplied material to a certain extent and large size, but the problem is the life of the water-cooled copper mold and the difficulty of maintenance. is there. That is, since it is water-cooled, there is a danger of steam explosion when water leaks,
In addition, it is difficult to perform inspections and replacements during maintenance.

Further, the above method (2) can be said to be a method that reduces the risk of steam explosion. In this method, a graphite container is used as a melting crucible, and a high-frequency coil is wound around the graphite crucible to heat the graphite to melt the hull in the crucible. But,
Since this is a method of indirectly heating the inner hull by heating the graphite crucible, the hull having a melting point of 1860 ° C. exceeds the melting limit of the crucible and cannot be melted.

On the other hand, there is a means for melting high melting point zircaloy or zircaloy metal at a low temperature. This method is a eutectic melting reaction. That is, the melting point of a high melting point metal is lowered by utilizing the eutectic reaction. In the case of zirconium and zircaloy metal, typical eutectic reaction-forming metals include the combinations of metals shown in Table 1. Do {(3) HETALLURGY AND metallurgical ENGINEARING
SERIES “CONSTITUTION OF BINARY ALLOYS” HCGRAW
HILL BOOK CO, INC, (1958)}.

That is, Table 1 shows that zirconium elemental metal is 1200 ° C.
The addition conditions of the additive material that can achieve the following melting points are shown. However, these phase diagrams have not been sufficiently investigated when zirconium metal itself is not a general metal in the case of zirconium, and the behavior of three or more combinations is unknown.
The table does not provide all satisfactory information.

Table 2 shows zirconium metal and eutectic material reaction conditions. In the same table, the values shown in the above (2) indicate that when melting in a graphite crucible, even if the melting point is lowered, Emphasis is placed on non-reactive combinations, and as a result, copper is used. However, this method was able to lower the melting point and avoid direct contact with the water-cooled part compared with (1) above, but if the graphite crucible was melted several times, the graphite crucible would be eroded and heated. However, there is a problem that the crucible is damaged as a result of the thermal shock at the time and the crucible is generated as secondary waste.

In the treatment of radioactive waste, the generation of this secondary waste should be avoided as much as possible. As a result, it is inferred that it melts in the graphite crucible and is cooled as it is, and the graphite crucible is used as a storage container (canister) together with the melt. The idea of storing arises. In this case, there are problems that the graphite crucible is weak in mechanical strength, that when the opening of the crucible is covered, it cannot be welded or the like and cannot be sealed, and the possibility of damage due to thermal shock remains.

The method for stabilizing the radioactive waste of zirconium simple substance and zirconium alloy has been developed for practical use in both the HIP method and the melting method, but the process is complicated, and the range of objects to be treated is narrow. There are problems such as explosion risk and generation of secondary waste.

(Object of the Invention) A first object of the present invention is to provide a melting method which eliminates the complexity of the process and expands the range of the object to be treated.

A second object of the present invention is to provide a melting method in which the danger of steam explosion is eliminated by adopting a heating method such as silicon carbide (SiC) or a nichrome heater that generates radiant heat as a heating source.

A third object is to provide a melting method in which a melting crucible uses a metal crucible that also serves as a storage container during storage.

A fourth object is to provide a melting method that employs a eutectic melting method as a means for lowering the melting points of zirconium simple substance and zirconium alloy in order to carry out the melting treatment at a melting temperature of the metal crucible or lower.

(Structure of the Invention) The present invention is to form an object to be treated containing zirconium or a zirconium alloy in a container, which is made of the same material as the eutectic material together with the eutectic material, is compressed by a pressing device, and is then compressed with a metal. It is placed in a crucible and heated in an inert gas atmosphere in a heating furnace to melt the object to be treated, and after cooling, a lid is attached to the metal crucible and the metal crucible is sealed and transferred to a predetermined storage location. Is. As the eutectic material, it is preferable to use a material that reacts with the object to be treated at 1200 ° C. or lower. Further, it is preferable to form the container for containing the object to be treated and the eutectic material with the same material as the eutectic material.

Further, the atmosphere in the heating furnace is heated as an inert gas atmosphere, the heating temperature in the heating furnace is set to 1200 ° C. or lower, and the addition amount of the eutectic material is set to 50% by weight or lower The eutectic material and the eutectic material are preferably cut into small pieces and housed in the container.

(Embodiment) This invention is basically such that a material to be treated such as a waste containing zirconium or a zirconium alloy is stored in a container together with a eutectic material, compressed by a pressing device, and then placed in a metal crucible. The metal crucible is housed in a metal crucible and heated in a heating furnace to melt the object to be processed, and after cooling, the metal crucible is attached to a lid, sealed and transferred to a predetermined storage place.

In the above treatment method, it is desirable that the heating temperature is as low as possible. When iron is used as the eutectic material, the melting temperature is 947 ° C. as shown in Table 2, but various deposits are present in the object to be treated. And the shape of the object to be treated is complicated, and it is difficult to create ideal reaction conditions. Further, considering the range of materials that can be used as the eutectic material and the mixing ratio, and the heat resistance of the metal crucible, the heating temperature is appropriately in the range of 1000 to 1200 ° C.

Further, the amount of the eutectic material added is preferably as small as possible for the purpose of volume reduction, and practically 50% by weight or less. As the eutectic material selected from this point of view, beryllium, copper, iron, manganese, and nickel are listed from Table 1, and SU having a large amount of nickel as an alloy material is used.
S316, Inconel, etc. can also be adopted. As for these shapes, a plate, a foil, a wire, a rod, a tube or a granular material can be adopted.

In order to make these eutectic materials react well with the object to be treated, prevent the reaction between the eutectic material and the metal crucible, and further improve the volume reduction, firstly, the object to be treated and the eutectic material are And are stored in a capsule container and compression molded by a pressing device.

Secondly, the capsule container is made of a eutectic material.

Thirdly, the compressed body of the capsule container is put into a metal crucible and melted.

Further, the compression by the press increases the bulk density of the filling in the metal crucible and improves the processing amount, and also improves the contact efficiency between the object to be processed and the eutectic material.

Further, since the metal crucible plays a role as a storage container and a crucible for melting, the shape of the metal crucible is preferably a cylindrical shape which can be easily processed. Further, it is important that the metal crucible does not react with the zirconium metal and the eutectic material which are the main components of the object to be treated at least at 1200 ° C or lower. The inner surface of the crucible may be coated with an inorganic substance such as alumina, zirconia, or boron nitride, or may be the metal itself. Molybdenum and tantalum can be used as the material of the crucible. That is, from the reference material of (3) above,
As shown in Table 3, molybdenum and tantalum are mixed with one of zirconium, iron, copper, and nickel.
It does not react when contacted at a temperature below 0 ° C.

Therefore, as the metal crucible, a metal container made of molybdenum or tantalum or a container of which the inner surface is lined, for example, a stainless steel of a laminated material (clad) is adopted. As this stainless steel, an austenitic stainless steel of iron-chromium-nickel alloy, an austenitic-ferritic alloy containing a small amount of nickel of 3.00 to 6.00% by weight, a high chromium content and a few% of molybdenum added. There are stainless steel, iron-chromium alloy ferritic stainless steel, and martensitic stainless steel.

On the other hand, as a means for reducing the manufacturing cost, it is also possible to directly use the above-mentioned austenite-ferritic stainless steel, ferritic stainless steel, and martensitic stainless steel by adding a eutectic material. The main components of these stainless steels are iron and chromium, and if nickel is selected as the eutectic material, they can be safely used as shown in Table 4. The cobalt metal can be used as a container made of austenitic stainless steel containing a large amount of nickel or a container made of a high nickel-base heat-resistant metal by lining the inner surface of the container.

On the other hand, when copper is used as the eutectic material, as shown in Table 5,
Since iron and cobalt react at 1200 ° C. or lower, an iron-chromium container or a cobalt lining container cannot be used.

In addition, as a means for preventing a direct reaction between the metal crucible and the eutectic molten metal, an inorganic material such as alumina (Al ₂ O ₃ ) or boron nitride (BN), which is a non-metal substance, is plasma-sprayed on the inner surface of the metal crucible. May be used for coating.

In FIG. 1, a nuclear fuel cladding tube made of zircaloy metal, which is an alloy of zirconium and tin, was used as the material for the zirconium object 1. BWR as its specification
(8 x 8R) size Zircaloy-2 rolls (outer diameter 12.
27, thickness 0.86 mm, length 30 mm) was used.

As the eutectic material 2, a pure nickel plate (thickness: 0.5 mm) was used to manufacture two capsule containers (inner diameter: 119 mm, height: 230 mm, with a bottom plate).
A piece cut into ~ 4 cm pieces was used.

Then, as shown in FIG. 1 (A), a capsule container 3 made of a nickel plate is appropriately mixed with an object to be treated 1 made of a Zircaloy short tube and a eutectic material 2 made of nickel pieces. Supplied. The amount of supply at this time was 2.1 kg per capsule container for a short tube and 0.19 k for nickel pieces.
It was set to g. As a result, the proportion of nickel in the capsule container 3 was 24% by weight. The amount added is preferably 17% by weight in order to lower the melting point as much as possible, but the addition range of the melting point to 1200 ° C. or lower by addition of nickel is 7 to 32% by weight as shown in Table 1. Here, since it is not fully understood how the reaction is performed, such an addition ratio is used.

Next, as shown in FIGS. 1 (B) and (C), the capsule container 3 accommodating the object to be treated 1 and the eutectic material 2 is transferred to a press device 4 with a die, and a 2500 kg / cm ² Original 2 by pressure
The capsule container 3 having a height of 30 mm was compressed and deformed to a height of 53 mm to obtain a compressed body 30. As shown in FIG. 1 (D), the other capsule containers were also compressed to have the same deformation amount.

Then, as shown in FIG. 1 (E), a compressed capsule container (compressed body 30) is provided with a metal crucible 5 made of SUS304 (outer diameter 150 mm, height 100 mm, thickness 5.6 mm).
I loaded two of them on top of each other. In this case, the inner surface of the metal crucible 5 was not particularly coated with tantalum or molybdenum.

The metal crucible 5 was placed in a heating furnace 6 and heated as shown in FIGS. 1 (F) and (G). This heating furnace 6
A heating source (for example, carbon) that generates radiant heat is arranged in a furnace surrounded by a heat insulating material (for example, graphite). The inside of the heating furnace 6 is sealed with 1
After degassing to about 0 ^-2 Torr and filling the inside of the furnace with argon gas 60, the inside of the furnace was filled with an inert gas, and a heating source was energized for heating. After heating to 1050 ° C., the temperature was maintained for 30 minutes, then the temperature was raised to 1100 ° C., and the temperature was maintained for 90 minutes. After that, the heating power source was cut off, and the furnace was cooled to room temperature while purging with argon gas.

Then, as shown in FIGS. 1 (H) to (J), the metal crucible 5 is taken out from the heating furnace 6 and sealed by attaching a lid 50, and the decontamination device 7 decontaminates the outer surface of the metal crucible 5. , As shown in FIG. 1 (K). When the metal crucible 5 is taken out from the heating furnace 6,
The internal compression body had a white metallic color, and the metal crucible 5 was not damaged at all.

FIG. 2 shows another embodiment, in which three compressed bodies 30 obtained in the steps of FIGS. 1 (A) to (D) are placed in a metal crucible 51 in an overlapping manner, and FIG. As shown in FIG. 2, a lid 53 having an exhaust pipe 52 was attached to seal the inside, and as shown in FIG. 2 (C), it was heated in a heating furnace 62 in the same manner as above. During this heat treatment, the exhaust pipe 52 was led out of the furnace, and the heating gas was discharged by the blower 55 through the pipe 54. Then, the metal crucible 5 is taken out from the heating furnace 62, and the exhaust pipe 52 is cut by the cutter 56 as shown in FIGS. 2 (D) and (E), and the cut portion is welded and sealed. It is stored in a predetermined storage area 8 as shown.

(Effects of the Invention) As described above, according to the present invention, an object to be treated containing zirconium or a zirconium alloy is housed in a container together with a eutectic material, compressed by a pressing device, and then housed in a metal crucible. Then, the object to be treated is melted by heating in a heating furnace, and after cooling, it is attached to the lid of the metal crucible, sealed, and transferred to a predetermined storage place. Is to have.

(1) No secondary waste of melting crucible is generated.

(2) There is no risk of steam explosion due to water cooling.

(3) It can be expected that the processing object, which is a characteristic of the dissolution processing, can be enlarged.

Due to the above characteristics, it is possible to safely, promptly and reliably industrially treat a large amount of waste containing zirconium or a zirconium alloy, which is expected to occur in the future.

[Brief description of drawings]

1 (A) to (K) are explanatory views of steps for carrying out the present invention, and FIGS. 2 (A) to (F) are explanatory views of steps showing another embodiment. 1 ... Object to be treated, 2 ... Eutectic material, 3 ... Capsule container,
4 ... Pressing device, 5, 51 ... Metal crucible, 6, 62
...... Heating furnace, 30 ...... Compressed body.

Claims (8)

[Claims] 1. An object to be treated containing zirconium or a zirconium alloy is housed together with a eutectic material in a container formed of the same material as the eutectic material, and compressed by a pressing device.
Then, this is placed in a metal crucible and heated in an oven under an inert gas atmosphere to dissolve the object to be treated, and after cooling, a lid is attached to the metal crucible, which is hermetically sealed and transferred to a predetermined storage place. A method for melt processing an object to be processed containing zirconium or a zirconium alloy. 2. A method for melting treatment of an object to be treated containing zirconium or a zirconium alloy according to claim 1, wherein a material which reacts with the object to be treated at 1200 ° C. or lower is used as the eutectic material. . 3. The zirconium or zirconium alloy according to claim 1 or 2, wherein the container for containing the object to be treated and the eutectic material is formed of the same material as the eutectic material. A method for melt processing an object to be processed, which comprises: 4. A melting treatment of an object to be treated containing zirconium or a zirconium alloy according to claim 1, 2, or 3, wherein the heating temperature in the heating furnace is 1200 ° C. or lower. Method. 5. An article to be treated containing zirconium or a zirconium alloy according to claim 1, 2, or 4, wherein the amount of the eutectic material added is 50% by weight or less. Melt processing method. 6. The object according to claim 1, 2, 3 or 5, wherein the object to be treated and the eutectic material are cut into small pieces and housed in the container. 1. A method for melt processing an object to be treated containing zirconium or a zirconium alloy. 7. The zirconium or zirconium alloy according to claim 1, 2, 3, or 5 characterized in that the metal crucible is coated with an inorganic material such as alumina or zirconia. A method for melt processing an object. 8. The heating means of the heating furnace is configured by disposing a heating source for generating radiant heat in a furnace surrounded by a heat insulating material. Item 3. A method for melting treatment of an object to be treated, which contains zirconium or a zirconium alloy according to Item 3 or 5.