JPH08313696A - Method for storing radioactive waste containing zircalloy - Google Patents

Abstract

PURPOSE: To realize the reduction of storing costs and, at the same time, make it possible to perfectly prevent fire caused by zircalloy fines. CONSTITUTION: In this method for storing radioactive wastes containing zircalloy by filling a container 7 with radioactive metal wastes containing zircalloy, it is made a rule to make oxygen insufficient in the container 7 filled with them and then store the container 7 by sealing it up. For the purpose, compacts H2 of the radioactive metal wastes are housed in the container 7, which is introduced into a main body 71 of a substitution welding device 70, and then is filled with an inactive gas by substituting it for the air in the main body 71. Subsequently, a lid 7a is welded to the container 7 to seal up the compacts H2 in it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention stores radioactive metal waste containing zirconium alloy such as spent zircaloy fuel cladding tubes and metallic materials generated during the reprocessing of spent fuel for light water nuclear reactors. It relates to a storage method.

[0002]

2. Description of the Related Art Zircaloy is an alloy mainly composed of zirconium, and has a small thermal neutron absorption cross-section, so that it is widely used as a reactor material, and is particularly preferably used as a fuel cladding tube for a nuclear reactor. . When reprocessing a fuel for a light water reactor, for example, which is loaded in a fuel cladding tube made of such a Zircaloy, first, an assembly of fuel cladding tubes loaded with spent fuel rods is cut. At that time, the fuel cladding tube is cut into several cm units, and the obtained strips are put into a melting tank, and in the melting tank, the nuclear fuel material, cladding fragment (hereinafter referred to as Zircaloyhal) and assembly parts (hereinafter Hardware)) and separate. The separated nuclear fuel material is sent to a processing step for reuse, and the remaining radioactive metal waste such as zircaloy hal and hardware is stored so that radioactivity does not leak outside.

By the way, zircaloy fines (dust) are generated from the zircaloy hull, but since this fine has a very strong ignitability, it is necessary to store it in a state where measures are taken to prevent ignition. As a fire prevention measure, a method of suppressing the generation of fines, a method of keeping the ignition source away from the hull at all, a method of storing the hull in a cooled state so that it is difficult to catch fire, and increasing the moisture content of the surrounding environment Possible methods include preventing the oxygen required for ignition from being given to the hull.

However, since zircaloyhal is embrittled by irradiation of radioactivity and fine particles are easily generated, it is very difficult to suppress the generation of fine particles. There is no effective way to suppress it. Even if the ignition source is kept away from the hull, energy necessary for ignition may be generated due to a fall accident in a storage facility or vibration due to an earthquake, which may become an ignition source. Furthermore, the method of storing the hull in a cooled state is
Although a reliable ignition prevention effect can be obtained by making the cooling temperature extremely low, there is a problem that enormous equipment cost and operation cost are required.

In contrast to these methods, the method of storing oxygen by shutting off oxygen necessary for ignition has a reliable effect of preventing ignition, and, compared with the method of storing the hull in an extremely low temperature cooled state, Economically advantageous. Further, as a method of storing the hull before the volume reduction treatment, the underwater storage method in which the hull is stored in water is the most popular. Specifically, radioactive metal waste such as zircaloy hull is generally stored in a stainless steel storage container called a hull can, and the hull can is also filled with water and stored in water. By doing so, the radiation caused by radioactive waste such as hulls is shielded, and the heat is removed and fines are prevented from firing.

[0006] However, the number of hull cans containing zircaloy hulls increases every time the spent nuclear fuel is reprocessed, so that there is a problem that the underwater storage facility will soon become full. ing. Therefore, we will reduce the volume of radioactive metal waste such as zircaloy hull stored in a hull to improve the storage rate of the storage space.
Attempts have been made to reduce the facility cost by adopting a so-called dry storage system, in which an inexpensive storage facility on the ground is used instead of an expensive storage facility in water. In the dry storage method, the radioactivity from radioactive waste such as hulls is protected by concrete shielding, etc., and heat is removed by air cooling.

[0007]

In the dry storage system, when a hull can for storage is handled, for example, when a drop accident occurs, the impact causes zircaloy fines to be generated in the hull can. However, there is a problem that the energy required for ignition is introduced by the impact, and as a result, zircaloy fines may react with oxygen in the hull can. In addition, if a hull can falls or the stacked hulls fall due to a natural disaster such as an earthquake during storage, zircaloy fines may be generated in the hull and react with oxygen in the can. It has a problem.

The present invention has been made in order to solve the problems of the above-mentioned dry storage system, contributes to the reduction of storage cost, and surely prevents ignition and explosion due to zircaloy fine. It is an object of the present invention to provide a method for storing radioactive waste containing zirconium alloy.

[0009]

According to a first aspect of the present invention, there is provided a method for storing radioactive waste containing zirconium alloy, which comprises storing the zirconium alloy containing the radioactive metal waste containing zirconium alloy in a storage container. In the method of storing radioactive waste, the method is characterized in that the storage container filled with the radioactive metal waste is made oxygen-deficient and then the storage container is sealed and stored.

The method for storing radioactive waste containing the zirconium alloy according to claim 2 of the present invention is the method for storing radioactive waste containing the zirconium alloy according to claim 1.
The oxygen-deficient state is formed by introducing an inert gas into the storage container.

A method for storing radioactive waste containing the zirconium alloy according to claim 3 of the present invention is the method for storing radioactive waste containing the zirconium alloy according to claim 1.
It is characterized in that the oxygen-deficient state is formed by degassing from the storage container.

The method for storing radioactive waste containing the zirconium alloy according to claim 4 of the present invention is the method for storing radioactive waste containing the zirconium alloy according to any one of claims 1 to 3, wherein the radioactive metal waste is used. It is characterized in that the volume is reduced before filling the storage container with the product.

The method for storing radioactive waste containing the zirconium alloy according to claim 5 of the present invention is the method for storing radioactive waste containing the zirconium alloy according to claim 4, wherein
The radioactive metal waste is loaded into a capsule in advance, the inside of the capsule is made oxygen-deficient, and then the volume of the capsule is reduced.

[0014]

According to the method for storing radioactive waste containing the zirconium alloy according to claim 1, after the storage container filled with the radioactive metal waste is made oxygen-deficient, the storage container is sealed and stored. Therefore, the ignition of zircaloy fines in the radioactive waste stored in the storage container is prevented.

According to the method for storing radioactive waste containing the zirconium alloy according to claim 2, since the inert gas is introduced into the storage container, the presence of the inert gas causes a shortage of oxygen in the storage container. The Zircaloy fines in the storage container are prevented from igniting.

According to the method for storing radioactive waste containing the zirconium alloy according to the third aspect, since the inside of the storage container is in an oxygen-deficient state due to degassing, ignition of zircaloy fine in the storage container is prevented. It

According to the method for storing radioactive waste containing the zirconium alloy described in claim 4, since the volume reduction process is performed before the radioactive metal waste is filled in the storage container, the radioactive metal waste is filled in the storage container. The filling rate of radioactive waste increases.

According to the method for storing radioactive waste containing the zirconium alloy according to the fifth aspect, the radioactive metal waste is loaded into the capsule in advance, the inside of the capsule is made oxygen-deficient, and then the volume of the capsule is reduced. Therefore, during the volume reduction process, the inside of the capsule is already in an oxygen-deficient state. If it does, Zircaloyhal will not catch fire due to lack of oxygen.

[0019]

EXAMPLE A radioactive waste storage method of the present invention is a radioactive metal waste containing zirconium alloy (zircaloy hull and hardware, hereinafter referred to as zircaloy hull only).
After the inside of the filled storage container is made oxygen-deficient, the storage container is sealed and stored. In order to carry out this method, in this embodiment, as shown in FIG. 1, a pretreatment process P1, a volume reduction process P2, a sealing process P3, and a storage process P4 are sequentially executed.

The above-mentioned pretreatment step P1 is a step of introducing the generated zircaloy-hal H into a capsule, degassing and then sealing the capsule to obtain a degassed sealed capsule H1. By enclosing it in a capsule in a vacuum state, ignition by Zircaloy fine generated in the capsule is surely suppressed during the processing operation of Zircaloy H in the subsequent steps. In this step, a degassing welding device is used that degasses the inside of the capsule and welds the lid.

The volume reducing step P2 is a step of compressing and reducing the volume of the degassed hermetically sealed capsule H1 obtained in the pretreatment step P1. In this step P2, a volume reduction processing device driven by hydraulic pressure is used, and the deaeration hermetically sealed capsule H1 is compressed by this volume reduction processing device to become a compression solidified body H2. In addition,
Even if the volume of the degassed hermetically sealed capsule H1 is reduced in this step P2, since the inside of the capsule is in a substantially vacuum state, the capsule is not damaged due to an increase in internal pressure. Therefore, the inflow of air into the compressed solidified body H2 does not occur, and the ignition suppression state of the zircaloy hull H is maintained.

In the volume reducing apparatus, if the degassed hermetically sealed capsule H1 is compressed while the inert gas is being supplied or being degassed, even if the capsule is damaged, the volume of the volume reducing process is still in progress. Ignition is prevented.

In the sealing step P3, the plurality of compressed and solidified bodies H2 formed in the volume reduction step P2 are stored in a storage container, and the air in the storage container is replaced with an inert gas to prevent the ignition. Is a step of obtaining. In this process, a pressure welding displacement welding apparatus is used. The inside of the displacement welding apparatus is degassed with the storage container loaded in the displacement welding apparatus, then the inert gas is supplied, and finally the lid is welded to the container body to be completely sealed. The supply of the above-mentioned inert gas may be omitted, and the lid may be welded at a stage where the inside of the storage container is in a substantially vacuum state.

The above-mentioned storage step P4 is a step of carrying in and storing the ignition-prevented storage container H3 obtained in the sealing step P3 into a storage box by using an appropriate transfer means. The zircaloy hull H stored in the storage is sealed in a compressed solidified body H2 in a vacuum state, and further, an inert gas is introduced into the ignition-prevented storage container H3, or the storage container H3 is evacuated. Since the ignition prevention treatment is performed twice, it is possible to reliably prevent the Zircaloy-hal H from igniting even if the inside of the storage is in an air environment.

The processing in each of the above steps will be described below.
This will be described in more detail with reference to FIGS. FIG. 2 is an explanatory view for explaining the pretreatment step, (a) is a state in which the capsule is filled with zircaloy-hal, (b) is a state in which the zircaloy-hal filled in the capsule is dried,
(C) is a state in which the capsule is degassed and sealed,
(D) shows the state in which the deaeration-sealed capsule is being conveyed to the next step.

In the pretreatment step P1, first, as shown in FIG. 2A, the zircaloy hull H, which is cut in advance to a predetermined size, has a cylindrical shape with a bottom arranged on the floor F at a predetermined position. It is supplied to the stainless steel capsule C of FIG. When the inside of the capsule C is filled with Zircaloy-Hull H, the capsule C is introduced into the drying chamber 12 as shown in FIG. The zircaloy hull H in the capsule C is dried in the drying chamber 12, and after the drying is completed, the stainless steel lid C1 is put on and introduced into the degassing welding device 13.

As shown in FIG. 2C, the degassing welding apparatus 13 has a cylindrical main body 14 having an open top, a sealing lid 15 for closing the upper opening of the main body 14, and an electric motor. A rotary table 16 which is rotated by driving, and a welding means 17 which is fixed to the upper peripheral wall of the main body 14 in a penetrating state.
It consists of and. The bottom of the main body 14 is provided with a suction hole 14a communicating with an unillustrated suction means, and the air in the main body 14 is sucked and removed by driving the suction means. Further, the welding means 17 is arranged so that the welding torch faces the joining portion between the upper edge portion of the capsule C and the peripheral edge portion of the lid C1 in a state where the capsule C is placed on the rotary table 16. The position is set.

Capsules C taken out from the drying chamber 12
After the lid C1 is attached, as shown in FIG. 2D, is introduced into the degassing welding device 13 and placed on the rotary table 16 with their axes aligned. It
Then, the sealing lid 15 is attached, and the inside of the main body 14 is deaerated by driving the suction means. And the main body 1
The rotary table 16 and the welding means 17 are driven after the inside of the chamber 4 is in a substantially vacuum state. These drives rotate the capsule C about the vertical axis, which causes the lid C to rotate.
1 is welded to the upper edge of the capsule C, and the inside of the capsule C becomes a deaeration-sealed capsule H1 in a substantially vacuum state.

When the above deaeration process is completed, the deaeration hermetically sealed capsule H1 is suspended by an appropriate suspending means 18 and then the main body 14 is suspended.
It is taken out from the vehicle, mounted on the truck 6 waiting on the rail 6a, and sent to the next volume reduction step P2.

FIG. 3 is a cross-sectional side view showing an example of the volume reduction processing apparatus used in the volume reduction process. As shown in this figure, the volume reduction apparatus 2 is installed on a base B projecting on the floor F. The volume reduction device 2 includes a base 21 arranged on the base B, a support frame 20 erected on the base 21, and the support frame 20.
And a cylindrical mold 3 that is supported so that it can move up and down.
The piston member 4 is slidably brought into contact with the inner wall surface of the cylinder 4 and is moved up and down. The cylinder 41 is supported by the support frame 20 and moves the piston member 4 up and down.

The mold 3 has an inner diameter slightly larger than the outer diameter of the capsule H1 so that it can be fitted onto the degassing hermetically sealed capsule H1. The mold 3 is connected to the lower end of the cylinder rod 32 of an elevating cylinder 31 fixed to the support frame 20 via a pedestal, and is moved up and down by driving the elevating cylinder 31.

A pretreatment step P is applied to the volume reducing apparatus 2 as described above.
The degassing hermetically-sealed capsule H <b> 1 loaded into the carriage 6 from 1 is arranged in the central portion of the base 21 while being mounted on the carriage 6. After that, when the elevating cylinder 31 and the pressing cylinder 41 are driven to lower the cylinder rod 32 and the piston member 4, the deaeration hermetically sealed capsule H1 is externally fitted by the mold 3, and the lowering of the piston member 4 in this state is continued. As a result, as shown by the chain double-dashed line, it is crushed on the carriage 6 to become the compressed and solidified body H2.

Even when a large amount of fines are generated from the zircaloy hull or the like in the deaeration hermetically sealed capsule H1 during the compression treatment of the deaeration hermetically sealed capsule H1, the fines are ignited because the capsule H1 is in a substantially vacuum state. There is no such thing. Further, since the inside of the capsule H1 is in a substantially vacuum state, the pressure inside the capsule H1 does not rise due to the above compression,
Therefore, breakage of the capsule H1 due to the pressure increase is unlikely to occur, and therefore the fine particles inside do not leak to the outside.

If the inert gas is introduced into the mold 3 through the inert gas introducing pipe 5 in a state where the mold 3 is lowered and fitted on the capsule H1, the capsule H1 should be taken. Even if is damaged, since the inert gas is introduced into the capsule H1, ignition by zircaloy fine is surely suppressed.

After that, the elevating cylinder 31 and the pressing cylinder 41 are driven in a synchronized state, and the cylinder rod 32 and the piston member 4 are raised, whereby the compressed and solidified body H2 is left on the carriage 6. By moving the carriage 6 in this state, the compressed and solidified body H2 is carried out from the volume reduction processing apparatus 2 and introduced into the next sealing step P3.

When the dolly 6 cannot withstand the compression process by the piston member 4, the degassing hermetically sealed capsule H1.
Alternatively, the carriage 6 may be carried to the lower part of the mold 3 and then the carriage 6 may be temporarily retracted, and the compression process may be performed with only the capsule H1 left on the base 21.

FIG. 4 is an explanatory view for explaining the treatment in the sealing step, (a) the state in which the compressed and solidified body obtained in the volume reducing step is being transferred by the suspending means, (b). Is the state where the compressed solidified body is being loaded into the storage container, (C)
Shows a state where the storage container is introduced into the replacement device, and (d) shows a state where the ignition-proof storage container is being transferred for storage.

The compressed and solidified body H2, which has been volume-reduced in the volume-reduction process P2 and is led out by the trolley 6, is suspended and transferred by the suspension means 19 and placed at a proper position on the floor F, as shown in (a). A plurality of them are introduced into the stored container 7. In this embodiment, six compression-solidified bodies H2 are stored in the storage container 7.
To store. Then, when the storage of the compressed and solidified body H2 in the storage container 7 is completed, the upper opening of the storage container 7 is closed by the lid 7a, and the storage container 7 is introduced and stored in the displacement welding device 70 as shown in (c). A substitution process is performed in which the air in the container 7 is replaced with an inert gas. The storage container 7 and the lid 7a are made of stainless steel.

The displacement welding device 70 is basically constructed in the same manner as the degassing welding device 13, and has a cylindrical main body 71 having an open upper portion and a sealing lid for closing the upper opening of the main body 71. 72, a rotary table 73 which is rotated by the drive of an electric motor, and a welding means 74 which is fixed to the upper peripheral wall of the main body 71 in a penetrating state.
An inert gas introducing pipe 75 connected to a supply pump (not shown) and a suction pipe 76 connected to a vacuum pump (not shown) are provided at the bottom of the main body 71 to operate the vacuum pump. The air in the main body 71 is sucked and removed by the main body 71 and the main body 7 is operated by operating the supply pump.
An inert gas is introduced into the inside of the chamber 1. In this embodiment, nitrogen gas is used as the inert gas, but helium gas or argon gas may be used instead of nitrogen gas.

In the welding means 74, the torch 74a for welding the storage container 7 placed on the rotary table 73 is provided between the upper edge portion of the storage container 7 and the peripheral edge portion of the sealing lid 72. The position is set so as to face the joining portion.

Then, the storage container 7 closed by the sealing lid 72 is introduced into the displacement welding device 70 and placed on the rotary table 73 with their axes aligned. After that, the sealing lid 72 is attached, and the air in the main body 71 is sucked and removed through the suction pipe 76 by driving the suction pump, whereby the inside of the main body 71 is brought into a substantially vacuum state. In this state, the inside of the storage container 7 is also in a substantially vacuum state.
The lid 7a may be attached to the storage container 7 before closing the sealing lid 72 or before loading the storage container in the displacement welding device 70.

Thereafter, the supply pump is driven, and the inert gas passes through the introduction pipe 75 and the main body 71 of the displacement welding device 70.
Introduced within. By this introduction, the storage container 7 is also filled with the inert gas. Then, after the sufficient inert gas is introduced into the storage container 7, the rotary table 73 and the welding means 74 are driven. These drives rotate the storage container 7 about the vertical axis, and the lid 7a is welded to the upper edge of the storage container 7 by this, and the storage container 7 is filled with an inert gas and has a fire prevention countermeasure. H3 is obtained.

Thereafter, as shown in FIG. 4D, the ignition-proof storage container H3 is hung by the hanging means 19a, taken out from the main body 71, and carried to a predetermined ground-based storage. Stored.

FIG. 5 is a partially cutaway side view showing an example of a storage container in which the compressed and solidified body is stored. As shown in this figure, a plurality of compression-solidified bodies H2 filled with zircaloy hull H and subjected to volume reduction are hermetically stored in a stacked state in a storage container H3 for which ignition has been prevented, In addition, since the storage container H3 is filled with an inert gas, the storage container H can be handled by handling before storage.
Even if 3 vibrates or the storage container H3 is accidentally dropped during transportation, and zircaloy fines are generated in the compressed and solidified body H2, as long as the storage container H3 is not damaged, the ignition of zircaloy fines is ensured. Be blocked.

Also, if an earthquake occurs during storage in the storage and the storage container H3 for which ignition measures have been stored collapses or the stacked ones fall, the storage container H3 will not be damaged as in the above case. Fine's ignition is surely suppressed.

In the above embodiment, the deaeration process in the capsule C is performed in the pretreatment process P1, but the deaeration process of the capsule C in the pretreatment process P1 is not always necessary in the present invention. Volume reduction process P2 with C left open
It may be subjected to the compression treatment in. However, in this case,
At the time of the compression treatment in the volume reduction step P2 and the subsequent handling, it is preferable to take ignition prevention measures such as keeping the capsule C in an inert gas atmosphere or an extremely low temperature atmosphere.

[0047]

According to the method for storing radioactive waste containing the zirconium alloy according to the first aspect of the present invention, the storage container filled with the radioactive metal waste is deficient in oxygen and then the storage container is opened. Since it is sealed and stored, the ignition of zircaloy fine in the radioactive waste stored in the storage container is surely blocked, and it is extremely effective in improving the safety of the stored radioactive metal waste. Is.

Further, since the inside of the storage container is in an oxygen-deficient state, it is possible to store in a storage facility installed on the ground, and it is not necessary to carry out underwater storage as in the conventional case, and the storage cost is reduced. It is convenient for reducing the amount.

According to the method for storing radioactive waste containing the zirconium alloy according to claim 2 of the present invention, since the inert gas is introduced into the storage container, the presence of this inert gas causes Oxygen is deficient, and ignition of zircaloy fines in the storage container is reliably prevented.

According to the method for storing radioactive waste containing the zirconium alloy according to the third aspect of the present invention, since the inside of the storage container is deficient in oxygen due to deaeration, the zircaloy fines in the storage container are ignited. Certainly blocked.

According to the method for storing radioactive waste containing the zirconium alloy according to the fourth aspect of the present invention, the volume reduction treatment is performed before the radioactive metal waste is filled in the storage container. The radioactive waste to be filled has a high filling rate, which is advantageous in reducing storage costs.

According to the method for storing radioactive waste containing the zirconium alloy according to the fifth aspect of the present invention, radioactive metal waste is loaded in the capsule in advance, and the capsule is depleted of oxygen, and then the entire capsule is reduced. Since the volume treatment is carried out, the inside of the capsule is already in an oxygen-deficient state at the time of the volume reduction treatment.Therefore, due to deformation or collision due to pressure during the volume reduction treatment, friction heat etc. Even if energy is generated, it is surely prevented that Zircaloyhal is ignited due to lack of oxygen.

[Brief description of drawings]

FIG. 1 is a process chart showing an example of a storage method of the present invention.

FIG. 2 is an explanatory diagram for explaining a pretreatment process,
(A) is a state in which the capsule is filled with zircaloy-hal, (b) is a state in which the zircaloy-hal filled in the capsule is dry, and (c) is a state in which the capsule is deaerated and is being sealed, (D) shows the state in which the deaeration-sealed capsule is being conveyed to the next step.

FIG. 3 is a side sectional view showing an example of a volume reduction processing apparatus used in a volume reduction process.

FIG. 4 is an explanatory diagram for explaining a sealing step,
(A) is a state in which the compressed and solidified body obtained in the volume reduction step is being transferred by the suspending means, (b) is a state in which the compressed and solidified body is being loaded into the storage container, and (c) is the storage container. The state of being loaded in the displacement welding apparatus, and (d) show the state in which the ignition-prevented storage container is being transferred for storage.

FIG. 5 is a partially cutaway side view showing an example of a storage container in which a compressed and solidified body is stored.

[Explanation of symbols]

 P1 Pretreatment process P2 Volume reduction process P3 Sealing process P4 Storage process H Degassing sealed capsule H1 Compressed solidified body H2 Compressed solidified body H3 Ignition countermeasure storage container C Capsule C1 Lid 1 Volume reduction processing device 11 Chute 12 Drying chamber 13 Desorption Air welding device 14 Main body 15 Closed lid 16 Rotary table 17 Welding means 2 Volume reduction device 20 Support frame 21 Base 3 Mold 31 Lifting cylinder 32 Cylinder rod 4 Piston member 41 Cylinder 6 Cart 7 Storage container 7a Lid 70 Replacement Welding device 71 Main body 72 Sealing lid 73 Rotating table 74 Welding means 75 Inert gas introduction pipe 76 Suction pipe

Claims (5)

[Claims] 1. A method for storing radioactive waste containing zirconium alloy, which comprises storing radioactive metal waste containing zirconium alloy in a storage container and storing the same, wherein the storage container filled with radioactive metal waste lacks oxygen. A method for storing radioactive waste containing a zirconium alloy, which comprises storing the storage container in a sealed state after being put into a state. 2. The method for storing radioactive waste containing a zirconium alloy according to claim 1, wherein the oxygen-deficient state is formed by introducing an inert gas into the storage container. 3. The method for storing radioactive waste containing a zirconium alloy according to claim 1, wherein the oxygen-deficient state is formed by degassing from the storage container. 4. The volume reduction process before filling the radioactive metal waste into a storage container.
A method for storing radioactive waste containing the zirconium alloy according to any one of 1. 5. The radioactive waste containing a zirconium alloy according to claim 4, wherein the radioactive metal waste is loaded in a capsule in advance, the inside of the capsule is made into an oxygen deficient state, and then the volume of the capsule is reduced. How to store things.