JP6746922B2 - Method and device for storing radioactive waste - Google Patents

Description

The present invention relates to a radioactive waste storage method and apparatus.

Radioactive waste such as fuel debris emitted from nuclear power plants is stored in a reinforced concrete building, for example, in a metal container called a canister, and stored for a predetermined period to remove decay heat. To be cooled.

As a document showing a general technical level regarding the storage method of this kind of radioactive waste, there is, for example, the following Patent Document 1.

JP, 11-211893, A

Radioactive waste is generally stored temporarily by water cooling. When the radioactive waste is stored, a treatment such as drying is performed prior to the storage, but hydrogen is generated when the radioactive waste contains water and organic substances. In particular, the material forming the cladding tube and the like are dissolved in the fuel debris in various states, and the fuel debris melted in the cladding tube continues to generate hydrogen for a long period. The fuel debris is crushed for storage, but depending on the crushed part, there are a part that generates a large amount of hydrogen and a part that generates a small amount of hydrogen. When the amount of hydrogen generated is large, it is necessary to take measures to reduce the hydrogen concentration during storage.

In view of such circumstances, the present invention intends to provide a radioactive waste storage method and device capable of keeping the hydrogen concentration around the radioactive waste low.

The present invention is
Radioactive waste is stored unsealed in an open canister with a recombination catalyst that combines hydrogen and oxygen inside the lid ,
The canister includes a main pipe that houses the canister, an inlet pipe that includes an inlet pump that supplies outside air into the main pipe, and an outlet pipe that includes an outlet pump that discharges the gas in the main pipe to the outside. Stored in a storage tube
During storage, the gas in the storage pipe is periodically sampled, and the gas in the storage pipe is exhausted from the outlet pipe to the outside according to the hydrogen concentration in the gas, and the outside air is introduced from the inlet pipe into the storage pipe. The present invention relates to a method of storing radioactive waste, in which the step of scavenging the storage pipe is performed by supplying air.

In the radioactive waste storage method of the present invention, it is preferable that the outlet pump also has a function of maintaining a negative pressure in the storage pipe.

The present invention also provides
An open-structured canister that has a recombination catalyst that bonds hydrogen and oxygen inside the lid and that stores radioactive waste inside without sealing it,
A main pipe for accommodating the canister therein; an inlet pipe having an inlet pump for supplying outside air into the main pipe; and an outlet pipe having an outlet pump for discharging the gas in the main pipe to the outside. With a storage tube,
The gas in the storage pipe is periodically sampled, and the gas in the storage pipe is exhausted from the outlet pipe to the outside according to the hydrogen concentration in the gas, and the outside air is supplied from the inlet pipe into the storage pipe. A radioactive waste storage device configured to perform a scavenging process.

According to the radioactive waste storage method and apparatus of the present invention, the excellent effect that the hydrogen concentration around the radioactive waste can be kept low can be obtained.

1 is an overall schematic view showing an embodiment of a radioactive waste storage method and device of the present invention. It is a figure which shows the storage pipe in the Example of the storage method and apparatus of the radioactive waste of this invention. It is a schematic diagram showing a neutron absorber arranged inside a canister in an embodiment of a method and an apparatus for storing radioactive waste of the present invention, (A) shows the neutron absorber so as to cover an inner wall surface of the canister. FIG. 3B is a side sectional view and a plan sectional view showing an example in which the neutron absorbing material is disposed so as to project radially from the inner wall surface of the canister. It is a flowchart which shows the procedure of the storage method of the radioactive waste of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

1 to 3 show an example of the form of a radioactive waste storage method and apparatus according to the present invention. In the present embodiment, as shown in FIG. 1, a plurality of canisters 2 containing the radioactive waste 1 are vertically housed in a storage pipe 3, and the storage pipes 3 are stored in a building 4 and the inside of the building 4 is stored. The canister 2 or the storage pipe 3 in which the radioactive waste 1 is stored is air-cooled by natural ventilation.

The building 4 includes an inlet shaft 5 that forms a flow path that communicates with the outside below the storage portion of the storage pipe 3, and an outlet shaft 6 that communicates with the outside above the storage pipe 3. Air containing heat is discharged from 6. That is, the air in the building 4 is warmed by the decay heat generated from the radioactive waste 1, rises in the space in the building 4, and is naturally discharged from the outlet shaft 6, while the air is discharged from the lower inlet shaft 5 to the outlet. The outside air having a low temperature flows in along with the exhaust from the shaft 6. The outside air that has flowed into the inlet shaft 5 is warmed by the decay heat, rises, and is discharged from the outlet shaft 6. In this way, the canister 2 or the storage pipe 3 is naturally air-cooled by the draft force of the outside air generated by the decay heat during the storage process in the building 4.

Further, in the case of the present embodiment, each storage pipe 3 is provided with an inlet pipe 8 below the main pipe 7 for storing the canister 2 and an outlet pipe 9 above the main pipe 7 as shown in FIG. It is configured so that the inside can be scavenged by exhausting from 9 and taking in outside air from the inlet pipe 8.

The inlet pipe 8 includes an inlet filter 10 having a pre-filter and a HEPA filter (High-Efficiency Particulate Air Filter), and an inlet pump 11 that draws outside air into the main pipe 7 through the inlet filter 10. A check valve 12 is provided between the inlet filter 10 and the inlet pump 11.

Similarly, the outlet pipe 9 is provided with an outlet filter 13 having a pre-filter and a HEPA filter, and an outlet pump 14 for exhausting the gas in the main pipe 7 to the outside through the outlet filter 13. Further, the outlet pipe 9 is provided with a check valve 15 at a position on the upstream side of the outlet pump 14, and a pressure gauge 16 for measuring the internal air pressure between the check valve 15 and the outlet pump 14.

The main pipe 7 can be housed inside by stacking the canisters 2 from the upper opening 7a in the vertical direction, and the upper opening 7a can be closed by a shielding plug 17 having a gasket structure. There is. The outlet pipe 9 is provided on the side surface of the main pipe 7 so as not to prevent the canister 2 from entering and exiting through the upper opening 7a.

The canister 2 housed in the housing pipe 3 has, for example, a structure as shown in FIG. 3(A) or FIG. 3(B). In the case of the present embodiment, the canister 2 is adapted to house the radioactive waste 1 such as fuel debris in an unsealed state. That is, the lid 18 provided in the canister 2 is for isolating the radioactive waste 1 in the canister 2, but the lid 18 of the present embodiment does not have a gasket for keeping the canister 2 airtight and can leak. Has an open structure. With the canister 2 having such an open structure, the gas generated from the radioactive waste 1 can escape to the space inside the storage pipe 3. That is, the “non-sealing state” of the canister 2 in this specification refers to a state in which at least gas can leak from the inside of the canister 2. Therefore, for example, the lid 18 may be provided with a filter so that the solid radioactive waste 1 is held inside the canister 2 so as not to leak, while the gas can be leaked to the outside through the lid 18.

A recombination catalyst 19 that bonds hydrogen and oxygen is provided inside the lid 18. With this recombination catalyst 19, hydrogen generated in the canister 2 by radiolysis of water is recombined with oxygen to return to water, and the increase in hydrogen concentration in the storage pipe 3 or the canister 2 is suppressed as much as possible. There is. When the lid 18 or the canister 2 has an open structure, light hydrogen is selectively released from the canister 2 so that the hydrogen concentration inside the canister 2 can be maintained at a level that does not cause a problem. 19 may not be needed.

A neutron absorbing material 20 is arranged inside the canister 2. The neutron absorbing material 20 can be disposed so as to cover the inner wall surface of the canister 2 as shown in FIG. 3(A), for example. Alternatively, for example, as shown in FIG. 3(B), the canister 2 may be radially extended from the inner wall surface and may be arranged at equal intervals in the circumferential direction of the canister 2. As the neutron absorbing material 20, various materials having a property of absorbing neutrons can be used. For example, a sintered material obtained by adding boron oxide to aluminum alloy powder and performing heat treatment can be used.

Next, the operation of this embodiment described above will be described with reference to the flowchart of FIG.

The radioactive waste storage method and apparatus of the present embodiment is capable of scavenging the inside of the canister 2 or the storage pipe 3, and is suitable when the amount of hydrogen generated from the radioactive waste 1 is relatively large. .. That is, as described above, the properties of the radioactive waste 1 such as fuel debris vary, and depending on the content of hydrogen due to the melting of the cladding tube, the water content, the amount of radiation generated, and other conditions, the generation of hydrogen during storage The amount will also be different. Here, when the amount of hydrogen generated from the radioactive waste 1 is expected to be sufficiently small, the radioactive waste 1 can be housed in a sealed state without using the present invention. When the generated amount is relatively large, it is effective to store the radioactive waste 1 in an unsealed state and appropriately discharge generated hydrogen by scavenging to prevent ignition. Specifically, if the hydrogen concentration in the air exceeds 4%, there is a risk of ignition, so if the hydrogen concentration in the atmosphere is expected to reach that value when it is assumed to be stored in a sealed environment. Therefore, it is desirable to store the radioactive waste 1 by the storage method or device as in this embodiment. For example, prior to storage, a part of the radioactive waste 1 is sampled, irradiated with radiation, and a test for confirming the amount of hydrogen generated is performed. As a result, in consideration of the capacity of the recombination catalyst 19 and the like, when it is determined that the hydrogen concentration in the space may reach 4% if it is stored in a closed state, the canister 2 and the storage pipe as in the present embodiment are obtained. Storage according to 3 may be selected.

In storage, first, as step S1 (see FIG. 4), the radioactive waste 1 is stored in the canister 2 as shown in FIGS. 3(A) and 3(B). After closing the opening of the canister 2 with the lid 18 so as not to seal it, in step S2 (see FIG. 4), the canister 2 is housed in the main pipe 7 of the housing pipe 3 and the upper opening 7a is shielded as shown in FIG. Seal at 17. Then, in step S3 (see FIG. 4), the storage pipe 3 storing the canister 2 is stored in the building 4 as shown in FIG.

During storage, hydrogen is generated from the radioactive waste 1 due to radiolysis of water and the like. The generated hydrogen is combined with oxygen by the recombination catalyst 19 and returned to water to some extent, but when hydrogen is generated at a rate exceeding the capacity of the recombination catalyst 19, the hydrogen concentration in the atmosphere of the radioactive waste 1 increases. I will do it. Since the gas in the canister 2 can leak, the generated hydrogen leaks from the canister 2 and gradually fills the storage pipe 3.

Therefore, in order to prevent ignition, hydrogen is discharged from the storage pipe 3 in step S4 (see FIG. 4). In this embodiment, by operating the outlet pump 14, the gas in the storage pipe 3 can be exhausted from the outlet pipe 9 to the outside (see FIG. 2 ). Here, since hydrogen is light, it tends to be distributed upward in the storage pipe 3, and is efficiently exhausted from the outlet pipe 9 provided above the main pipe 7. At this time, since the outlet pipe 9 is provided with the outlet filter 13, the radioactive substance in the storage pipe 3 does not leak to the outside. In addition, the outlet pump 14 also serves to keep the inside of the storage tube 3 at a negative pressure because the radioactive material is contained therein.

Here, in order to keep the hydrogen concentration in the storage pipe 3 low, the exhaust from the outlet pipe 9 is insufficient. Therefore, in the present embodiment, in addition to the exhaust from the outlet pipe 9 in step S4, in step S5, the outside air is supplied from the inlet pipe 8 into the storage pipe 3 so that the storage pipe 3 is scavenged. (See Figure 4). By the scavenging process including steps S4 and S5, the hydrogen concentration in the storage pipe 3 can be effectively reduced.

In this scavenging process, the temporal relationship between step S4 and step S5 is not particularly limited. Exhaust from the outlet pipe 9 may be performed first, or air supply from the inlet pipe 8 may be performed first. Further, the exhaust from the outlet pipe 9 and the air supply from the inlet pipe 8 can be performed in parallel. In any case, of course, it is desirable to keep the inside of the storage tube 3 at a negative pressure through this scavenging process.

The scavenging steps of steps S4 and S5 may be performed, for example, at regular intervals, or the gas in the storage tube 3 is periodically sampled to detect that the hydrogen concentration has risen to a predetermined value. It may be executed at a timing. Alternatively, it can be executed at the timing when the value of the pressure gauge 16 reaches a predetermined value.

As described above, during storage in the building 4, the canister 2 or the storage tube 3 is naturally air-cooled by the draft force generated by the decay heat (see FIG. 1). This air cooling is performed by the air taken in from the inlet shaft 5 passing around the storage pipe 3, and the passed air is discharged from the outlet shaft 6 to the outside of the building 4. At this time, the storage pipe 3 has the upper opening 7a of the main pipe 7 sealed by the shield plug 17, and the inlet pipe 8 and the outlet pipe 9 are provided with the inlet filter 10 and the outlet filter 13 so that only gas passes therethrough. Therefore, the radioactive material does not leak to the air passing through the building 4. In this way, the flow of air for cooling the decay heat and the flow of air for scavenging are separated into the outside and the inside of the storage pipe 3.

Thus, according to the present embodiment described above, the hydrogen concentration around the radioactive waste 1 can be kept low.

Further, in this embodiment, the outlet pump 14 also serves to keep the inside of the storage pipe 3 at a negative pressure. With this configuration, the radioactive substance can be reliably contained in the storage tube 3.

Furthermore, if the gas in the storage pipe 3 is periodically sampled and the step of scavenging the storage pipe 3 is executed according to the hydrogen concentration in the gas, ignition due to an increase in hydrogen concentration is ensured. It can be avoided.

The radioactive waste storage method and apparatus of the present invention are not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the scope of the present invention.

1 Radioactive waste 2 Canister 3 Storage pipe 7 Main pipe 8 Inlet pipe 9 Outlet pipe 11 Inlet pump 14 Outlet pump

Claims (3)

Radioactive waste is stored unsealed in an open canister with a recombination catalyst that combines hydrogen and oxygen inside the lid ,
The canister includes a main pipe that houses the canister, an inlet pipe that includes an inlet pump that supplies outside air into the main pipe, and an outlet pipe that includes an outlet pump that discharges the gas in the main pipe to the outside. Stored in a storage tube
During storage, the gas in the storage pipe is periodically sampled, and the gas in the storage pipe is exhausted from the outlet pipe to the outside according to the hydrogen concentration in the gas, and the outside air is introduced from the inlet pipe into the storage pipe. A method for storing radioactive waste, wherein the step of scavenging the storage pipe is performed by supplying air. The method for storing radioactive waste according to claim 1, wherein the outlet pump also serves to keep the inside of the storage tube at a negative pressure. An open-structured canister that has a recombination catalyst that bonds hydrogen and oxygen inside the lid and that stores radioactive waste inside without sealing it,
A main pipe for accommodating the canister therein; an inlet pipe having an inlet pump for supplying outside air into the main pipe; and an outlet pipe having an outlet pump for discharging the gas in the main pipe to the outside. With a storage tube,
The gas in the storage pipe is periodically sampled, and the gas in the storage pipe is exhausted from the outlet pipe to the outside according to the hydrogen concentration in the gas, and the outside air is supplied from the inlet pipe into the storage pipe. A radioactive waste storage device configured to perform a scavenging process.

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