JP2003139887A - Canister - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a canister having high air-tightness and capability of easily confirming air-tightness. SOLUTION: The canister 10 is provided with a nearly cylindrical vessel body 14 containing radioactive materials, and the vessel body has a closed bottom end and an open top end and a flange 12 placed around the top open end. In the open top end of the vessel body, a primary lid 28 is installed and its edge part is welded to the inner surface of the vessel body. On the top open end of the vessel body, a secondary lid 32 is also installed over the primary lid and fixed to the flange with bolts so as to provide a closed space for inspection 36 between it and the primary lid.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called canister, which is a hermetically sealed metal container for enclosing a radioactive substance that generates heat.

[0002]

2. Description of the Related Art Highly radioactive substances typified by spent fuel in nuclear reactors are reprocessed in order to recover useful substances such as plutonium that can be reused as fuel. Then, these spent fuels are temporarily stored in a sealed state until reprocessing. As a method for storing such highly radioactive substances, a wet method using a storage pool or the like, or
A dry method using a cask or the like is known.

The dry method is a storage method in which air is naturally cooled instead of water, and its operating cost is lower than that of the wet method. As a cask used in the dry method, a concrete cask that shields spent fuel by a concrete structure, a metal cask, or the like is known. These casks are provided with a cylindrical container body whose top and bottom are closed. Then, the spent fuel is enclosed in a cylindrical metal airtight container, a so-called canister, and further, the canister is stored in the container body of the cask described above, so that the spent fuel is stored in a state in which radioactive substances are shielded.

Usually, a canister has the above-mentioned metal closed container and a basket arranged in the closed container, and a plurality of spent fuels are supported in the closed container in the closed container. It is enclosed. Further, such a canister includes a cylindrical container body having a closed bottom surface and a lid that closes an upper opening of the container body. After the spent fuel is stored in the container body through the upper opening, a disc-shaped lid is dropped into the upper opening of the container body to close it, and the outer peripheral portion of this lid is welded to the container body. A canister that has the property of containing spent fuel is formed.

[0005]

In the canister as described above, if there is a welding defect in the welded portion of the lid, the strength of the welded portion is reduced, and radioactive material leaks from this defective portion to ensure the integrity of the canister. That is, it becomes difficult to maintain the radioactive substance sealing performance of the canister.

Therefore, it is important that the welded part of the lid has no welding defect and has a high hermeticity. At the same time, it is desirable that the canister be capable of easily confirming the hermeticity and being able to easily and reliably monitor the occurrence of defects in the welded portion and the leakage of radioactive material.

The present invention has been made in view of the above points, and an object thereof is to provide a hermetically sealed metal container having a high hermeticity and capable of easily confirming the hermeticity. .

[0008]

In order to achieve the above object, a canister according to an aspect of the present invention has a closed lower end, an upper end opening, and a flange provided around the upper end opening. Then, a substantially cylindrical container main body containing a radioactive substance, a primary lid mounted in the upper end opening of the container main body, the peripheral edge of which is welded to the inner peripheral surface of the container main body, and bolted to the flange. It is characterized in that the upper end opening is closed, and a secondary lid that defines a closed space for leak inspection is provided between the secondary lid and the primary lid.

A canister according to another aspect of the present invention has a closed lower end, an upper end opening, and a flange provided around the upper end opening, and has a substantially cylindrical shape containing a radioactive substance. -Shaped container main body, a primary lid mounted in the upper end opening of the container main body, the peripheral edge of which is welded to the inner peripheral surface of the container main body, and mounted in the upper end opening overlapping the primary lid, the peripheral edge being A secondary lid welded to the inner peripheral surface of the container body,
It is characterized in that it is provided with a tertiary lid which is bolted to the flange to close the upper end opening and which defines a sealed space for leak inspection between the secondary lid and the secondary lid.

Further, according to the canister of the aspect of the present invention, the primary lid has an outer peripheral portion that is adjacent to and faces the inner peripheral surface of the container body, and the outer peripheral portion is the inner peripheral surface of the container body. And a welded part welded to the bottom of the container body with respect to the welded part, and when welding the welded part, shield gas is filled or flowed to shield the welded part from the inside of the container body. It is characterized by having a space portion for performing.

According to the canister having the above construction, the secondary lid or the tertiary lid is bolted to the flange of the container body to define the closed space for the leak inspection, so that the leak inspection can be easily performed using this closed space. It is possible to confirm the tightness of the welded part. For example, set the closed space to negative pressure,
There are a method of inspecting the presence or absence of leakage gas and radiation from the container body, or a method of pressurizing the sealed space and confirming a change in the pressure.

This secondary lid or tertiary lid is always bolted to the flange of the container body, and is constantly attached to the container body by bolting to the flange only when inspecting for leakage or only during inspection. It may be configured.

Further, according to the canister according to the present invention, at the time of welding, by filling or flowing the shield gas in the space provided in the primary lid, it becomes possible to perform complete penetration welding of the welded portion, thereby ensuring a tight seal. A high weld can be obtained.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION A canister according to a first embodiment of the present invention will be described in detail below with reference to the drawings. As shown in FIGS. 1 and 2, the canister 10 as a metal closed container includes a substantially cylindrical container body 14 having a lower end closed by a bottom wall 15 and an upper end opening 14a. In addition, the container body 14
An annular flange 12 protruding outward is integrally formed around the upper end opening of the. The container body 14 is made of, for example, a metal such as stainless steel. A plurality of spent fuel assemblies 18 are enclosed in the container body 14 while being supported by the basket 16. These spent fuel assemblies 18 are, for example, spent fuel of a nuclear reactor, and include radioactive substances that generate heat due to decay heat and radiation. The canister 10 has a welded closed structure so that the enclosed radioactive substance does not leak outside.

That is, a plurality of, for example, four support bases 20 are fixed to the inner peripheral surface of the upper end portion of the container body 14 and are provided at equal intervals along the circumferential direction. An annular support plate 22 is placed on the support table 20. The support plate 22 has an outer diameter substantially equal to the inner diameter of the container body 14.

A disk-shaped shield plate 2 is provided on the support plate 22.
4 is placed and closes the upper end opening of the container body 14. A groove is formed on the entire outer periphery of the lower surface of the shielding plate 24, and an O-ring 26 made of a heat-resistant elastic material, ceramic or the like is fitted as a sealing material in the groove. The O-ring 26 is in close contact with the upper surface of the support plate 22 and hermetically seals the gap between the inner peripheral surface of the container body 14 and the shield plate 24.

A disk-shaped primary lid 28 is mounted in the upper end opening of the container body 14 so as to overlap the shielding plate 24, and closes the upper end opening of the container body. The upper end portion of the outer peripheral portion of the primary lid 28 is welded to the inner peripheral surface of the container body 14 over the entire circumference. As will be described later, the shielding plate 24 and the primary lid 28 are formed with exhaust holes 30 for use in exhausting air in the container body 14, draining water, and supplying air into the container body. The exhaust holes are fixed to the primary lid 28. It is sealed by the sealed plug body 31. Furthermore, on the outer peripheral portion of the primary lid 28,
As will be described later, a groove that defines a space for filling or flowing the shield gas at the time of welding is formed over the entire circumference and is located below the welded portion.

A disc-shaped secondary lid 32 is mounted on the upper end opening 14a of the container body 14 so as to overlap the primary lid 28 to close the upper end opening 14a. The peripheral portion of the secondary lid 32 is arranged so as to overlap the flange 12 of the container body 14, and is bolted to the flange by a plurality of bolts 34. A sealed space 36 for leak inspection is defined between the secondary lid 32 and the primary lid 28.

As shown in FIG. 3, an annular metal gasket 37 and an elastomer gasket 38 are provided inside the bolt 34 between the peripheral portion of the secondary lid 32 and the flange 12, and the secondary lid and the flange are provided. The space between them is hermetically sealed. Here, the metal gasket 37 is arranged inside the elastomer gasket 38. In addition, the secondary lid 32 is formed with an inspection port 40 that communicates between the metal gasket 37 and the elastomer gasket 38, and this inspection port enables inspection of the gasket's sealed state.

Thus, the upper end opening 1 of the container body 14
4a is airtightly closed by a shielding plate 24, a primary lid 28, and a secondary lid 32. The shield plate 24, the primary lid 28, and the secondary lid 32 are made of metal such as stainless steel. A leak inspection gas such as helium is sealed at a predetermined pressure in a sealed space 36 between the primary lid 28 and the secondary lid 32.

A method of loading the spent fuel assembly 18 into the canister 10 constructed as described above and a method of sealing the canister lid will be described below. First, FIG.
As shown in, the container body 14 having an upper end opening 14a
After filling the container with cooling water 42, the basket 1 is placed inside the container body.
6 and the spent fuel assembly 18 are arranged and immersed in the cooling water 42 to temporarily shield the spent fuel assembly with water. Then, the support plate 22 is inserted into the upper opening of the container body 14.
Then, the shielding plate 24 is sequentially mounted.

Subsequently, an appropriate amount of cooling water is drained from the container body 14 so that the water surface of the cooling water 42 is located slightly above the spent fuel assembly 18, and then the primary lid is attached to the container body 14. Put on 28. Here, as mentioned above,
Since the O-ring 26 is provided on the outer periphery of the lower surface of the shielding plate 24 and is in close contact with the support plate 22, the gap between the shielding plate 24 and the inner surface of the container body 14 is sealed from the inside of the container body by this O-ring. ing.

Further, as shown in FIGS. 4 to 6, at the outer peripheral portion of the primary lid 28, an upper end portion thereof forms a welded portion 44, and below the welded portion, that is, with respect to the welded portion. A groove 46 extending over the entire circumference is formed on the lower end side of the container body 14. Further, on the outer peripheral portion of the primary lid 28, there is formed an air supply hole 47 communicating with the groove 46 and opening to the upper surface of the primary lid 28. For example, two air supply holes 47 are provided in the circumferential direction of the primary lid 28 so as to be separated from each other.

In the state where the primary lid 28 is loaded, the outer peripheral portion of the primary lid is positioned adjacent to and faces the inner peripheral surface of the container body 14, and below the welded portion 44, an annular shape which is almost sealed by a groove 46. A space 48 is formed.

Subsequently, as shown in FIG. 7, after the primary lid 28 is attached, the upper peripheral edge portion of the primary lid is sequentially welded to the inner peripheral surface of the container body 14 by the welding device 70. This welding operation is performed in a state where the cooling water 42 remains in the container body 14 in order to shield radiation from the spent fuel assembly 18. Since it takes a long time to weld the primary lid 28, the cooling water 42 in the container body 14 is heated by the heat from the spent fuel assembly 18 and gradually evaporated during the welding operation. Then, the generated water vapor tends to flow toward the upper end opening side of the container body through the gap between the inner peripheral surface of the container body 14 and the primary lid 28. However, since the gap between the inner peripheral surface of the container body 14 and the primary lid 28 is sealed by the O-ring 26 provided on the shielding plate, the water vapor flowing into this gap is significantly reduced. Therefore, the primary lid 28 can be welded without causing welding defects due to water vapor.

Further, according to the present embodiment, when performing the welding work, the discharge holes 30 of the shield plate 24 and the primary lid 28 are provided.
Is used to attach the exhaust device 5, and the shield gas supply device 50 is connected to the air supply hole 47 of the primary lid 28.
Then, while the water vapor generated in the container body 14 is exhausted to the outside of the container body by the exhaust device 5, the shield gas is supplied to the space portion 48 formed by the groove 46 of the primary lid 28 by the shield gas supply device 50. In the flowed state, the welding device 70 welds the primary lid 28.

The shield gas supply device 50 includes a storage tank 52 that stores an inert gas such as argon as a shield gas, a gas supply pipe 54 connected to the air supply hole 47 of the primary lid 28, and a storage tank 52. And a pump 56 for supplying the shield gas inside to the air supply hole 47 via the gas supply pipe 54.

Then, during the welding operation, the shield gas is supplied by the shield gas supply device 50 to the space 48 formed below the welded portion 44 of the primary lid 28, and the space 48 is filled with the shield gas. Alternatively, the shield gas is made to flow. Therefore, this shield gas can shield the steam that is about to flow into the welded portion 44, and can more reliably prevent the steam from flowing into the welded portion. At the same time, complete penetration welding of the welded portion 44 becomes possible, and a welded portion with high sealing performance can be obtained.

After welding the primary lid 28 by the method described above, the cooling water 42 in the container body 14 is drained to the outside. Subsequently, after vacuum drying, inert gas replacement, sealing work and airtight leak test are performed on the inside of the container body 14, the discharge hole 30 of the primary lid 28 is sealed by the plug 31 as shown in FIG.

Then, the secondary lid 32 is attached to the upper end opening of the container body 14, and the secondary lid 32 is placed on the primary lid 28 in an overlapping manner. Then, the peripheral portion of the secondary lid 32 is attached to the flange 12 of the container body 14.
The upper end opening 14a is closed with a bolt, and a closed space 36 for leak inspection is defined between the primary lid 28 and the secondary lid 32. As a result, the spent fuel assembly 1
A canister 10 containing 8 is completed.

According to the canister 10 having the above structure, the hermeticity of the canister can be inspected and confirmed at the required time by utilizing the above-mentioned hermetically sealed space 36. For example, a periodic check during the storage period of the spent fuel, a constant monitoring, a sealability check, that is, a leak inspection is performed at the time of confirmation after transport after storage.

As a method for confirming the hermeticity, for example, the hermetically sealed space 36 is pressurized to a desired pressure and the pressure change is detected by a pressure sensor, or the hermetically sealed space 36 is used.
Can be set to a negative pressure, and a method of inspecting for leakage gas or radiation leakage from the container body can be used.

The secondary lid 32 is always bolted to the flange 12 of the container body 14 and is attached to the container body by bolting it to the flange only when monitoring for leakage or only during inspection. May be

According to the canister 10 having the above-described structure, the secondary lid 32 is bolted to the flange 12 of the container body 14 to define the closed space 36 for leak inspection, and this closed space is used. It is possible to easily perform leak inspection and confirm the tightness of the weld. Also, during welding,
By filling or flowing the shield gas in the space 48 provided in the primary lid 28, the primary lid 28 can be reliably welded without causing welding defects due to water vapor. At the same time, complete penetration welding of the welded portion is possible, and a welded portion with high sealing performance can be obtained. Therefore, in addition to having a high sealing property and excellent radiation shielding property,
It is possible to obtain a canister whose sealing property can be easily confirmed.

Next, the canister 10 according to the second to fourth embodiments of the present invention will be described. In these second to fourth embodiments, the canister 10
Each is configured to include a tertiary lid in addition to the primary lid and the secondary lid.

That is, as shown in FIG. 8, according to the canister 10 according to the second embodiment, the primary lid 2 is superposed on the shielding plate 24 in the upper end opening 14a of the container body 14.
8 is attached to close the upper end opening of the container body.
The peripheral edge portion on the upper end side of the primary lid is welded to the inner peripheral surface of the container body 14 over the entire circumference. Here, the primary lid 28 has a space portion 48 located below the welded portion 44 on the outer peripheral surface, as in the first embodiment. As will be described later, the shielding plate 24 and the primary lid 28 are formed with a discharge hole 30 used for exhausting and draining the inside of the container body 14, and the discharge hole is sealed by a plug body 31 fixed to the primary lid 28. ing.

Further, in the upper end opening of the container body 14,
A disc-shaped secondary lid 32 is mounted on the primary lid 28. The peripheral edge portion on the upper end side of the secondary lid 32 is welded to the inner peripheral surface of the container body 14, so that the secondary lid closes the upper end opening portion of the container body 14.

Further, a disk-shaped tertiary lid 60 is mounted on the upper end opening 14a of the container body 14 so as to overlap with the secondary lid 32 to close the upper end opening 14a. The peripheral portion of the tertiary lid 60 is arranged so as to overlap the flange 12 of the container body 14 and is bolted to the flange by a plurality of bolts 34. A sealed space 36 for leak inspection is defined between the tertiary lid 60 and the secondary lid 32.

Thus, the upper end opening 1 of the container body 14
4a is airtightly closed by the shielding plate 24, the primary lid 28, the secondary lid 32, and the tertiary lid 60. These shielding plate 24, primary lid 28, secondary lid 32, and tertiary lid 60
Is formed of a metal such as stainless steel. The other structure is the same as that of the first embodiment described above, and the same portions are denoted by the same reference numerals and detailed description thereof will be omitted.

According to the canister 10 configured as described above, after the spent fuel assembly 18 is loaded into the container body 14 by the same method as in the first embodiment described above, the primary lid 28 is closed. Weld to the container body. At this time, the space 48 of the primary lid 28 is welded while being filled or flowing with a shielding gas, and the welded portion of the primary lid 28 is completely welded. Subsequently, the secondary lid 32 is loaded in the upper end opening 14a of the container body 14, and the peripheral upper end portion is welded to the inner peripheral surface of the container body. Finally, the canister 10 is completed by attaching the tertiary lid 60 to the upper end opening 14a of the container body 14 and bolting it to the flange 12.

According to the canister constructed as described above, it is possible to obtain the same effects as those of the first embodiment described above. Further, by providing the secondary lid between the primary lid and the tertiary lid bolted to the flange of the container body, it is possible to obtain a canister having a higher hermeticity and an excellent radiation shielding property.

As in the third embodiment shown in FIG. 9, the secondary lid 32, like the primary lid 28, is a space portion provided on the lower end side of the container body 14 with respect to the welded portion 61. It may be configured to have 62, and at the time of welding the secondary lid 32, the space 62 may be filled or flowed with a shield gas to shield the welded portion from the inside of the container body.

Alternatively, as in the fourth embodiment shown in FIG. 10, the primary lid 28 and the secondary lid 32 are both
It is also possible to adopt a configuration having no space for filling or flowing the shield gas. Also in the third and fourth embodiments configured as described above, similar to the second embodiment, the sealing property is high and the radiation shielding property is excellent, and the sealing property can be easily confirmed. Can can be obtained.

The present invention is not limited to the above-described embodiments, but can be variously modified within the scope of the present invention. For example, in the first to fourth embodiments,
The configuration may be such that the shielding plate is omitted.

[0045]

As described above in detail, according to the present invention, the airtightness is high and the radiation shielding property is excellent.
It is possible to provide a canister whose sealing property can be easily confirmed.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view of a canister according to a first embodiment of the present invention.

FIG. 2 is a side view showing the canister with the upper end portion cut away.

FIG. 3 is an enlarged sectional view showing a flange portion of the canister.

FIG. 4 is a cross-sectional view showing a process of mounting the shielding plate and the primary lid of the canister.

FIG. 5 is a perspective view showing the primary lid of the canister partially cut away.

FIG. 6 is an enlarged sectional view showing an outer peripheral portion of the primary lid.

FIG. 7 is a cross-sectional view showing a step of welding the primary lid of the canister.

FIG. 8 is a side view showing a canister according to a second embodiment of the present invention with its upper end portion cut away.

FIG. 9 is a side view showing a canister according to a third embodiment of the present invention with its upper end portion cut away.

FIG. 10 is a side view showing a canister according to a fourth embodiment of the present invention with its upper end portion cut away.

[Explanation of symbols]

5 ... Exhaust device 10 ... Canister 12 ... Flange 14 ... Container body 18 ... spent fuel assembly 28 ... Primary lid 32 ... Secondary lid 36 ... Closed space 44 ... Welded part 46 ... Groove 48 ... Space 50 ... Shield gas supply device 60 ... tertiary lid 70 ... Welding equipment

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G21F 5/00 D (72) Inventor Kazuo Murakami 1-1-1 Wadazaki-cho, Hyogo-ku, Kobe-shi, Hyogo Mitsubishi Heavy Industries, Ltd.Kobe Shipyard (72) Inventor Koichi Kami 1-1-1 Wadazaki-cho, Hyogo-ku, Kobe-shi, Hyogo Mitsubishi Heavy Industries Ltd. Kobe Shipyard (72) Inventor Takashi Shige 2 Niihama, Arai-cho, Takasago-shi, Hyogo Prefecture 1-1-1 Mitsubishi Heavy Industries, Ltd. Takasago Research Institute (72) Inventor Kita Etsura 1-1-1 Wadazaki-cho, Hyogo-ku, Kobe, Hyogo Prefecture Mitsubishi Heavy Industries Ltd. Kobe Shipyard (72) Inventor Shizuo Inoue Hyogo 1-1 1-1 Wadasaki-cho, Hyogo-ku, Kobe-shi, Japan Inside Mitsubishi Heavy Industries, Ltd. Kobe Shipyard

Claims (8)

[Claims] 1. A substantially cylindrical container main body having a closed lower end, an upper end opening, and a flange provided around the upper end opening, and containing a radioactive substance, and an upper end of the container main body. For a leakage inspection between the primary lid that is installed in the opening and the peripheral edge is welded to the inner peripheral surface of the container body, and the flange is bolted to close the upper end opening and the primary lid. A canister characterized by having a secondary lid that defines a closed space of. 2. The primary lid has an outer peripheral portion adjacent to and facing the inner peripheral surface of the container body, the outer peripheral portion being a welded portion welded to the inner peripheral surface of the container main body, and the welded portion. Is provided on the lower end side of the container body against, when welding the welded portion,
The canister according to claim 1, further comprising a space portion for filling or flowing a shield gas to shield the welded portion from the inside of the container body. 3. The canister according to claim 2, wherein the primary lid includes a groove that is formed over the entire circumference of the outer peripheral portion and defines the space portion. 4. A substantially cylindrical container body having a closed lower end, an upper end opening, and a flange provided around the upper end opening, the container body containing a radioactive substance, and the upper end of the container body. A primary lid that is mounted in the opening and has a peripheral edge welded to the inner peripheral surface of the container body; and a secondary lid that is mounted in the upper end opening overlapping the primary lid and the peripheral edge is welded to the inner peripheral surface of the container main body. A secondary lid and a tertiary lid that is bolted to the flange to close the upper end opening and defines a sealed space for leakage inspection between the secondary lid and the secondary lid. Canister to do. 5. The primary lid has an outer peripheral portion adjacent to and facing the inner peripheral surface of the container body, the outer peripheral portion being a welded portion welded to the inner peripheral surface of the container main body, and the welded portion. Is provided on the lower end side of the container body against, when welding the welded portion,
The canister according to claim 4, further comprising a space portion for filling or flowing a shield gas to shield the welded portion from the inside of the container body. 6. The secondary lid has an outer peripheral portion adjacent to and facing the inner peripheral surface of the container body, the outer peripheral portion being a welded portion welded to the inner peripheral surface of the container body, and the welded portion. Is provided on the lower end side of the container body with respect to the portion, when welding the welded portion,
The canister according to claim 5, further comprising a space portion for filling or flowing a shielding gas to shield the welded portion from the inside of the container body. 7. The canister according to claim 5, wherein the primary lid includes a groove that is formed over the entire circumference of the outer peripheral portion and defines the space portion. 8. The canister according to claim 6, wherein the secondary lid is provided with a groove formed over the entire circumference of the outer peripheral portion and defining the space portion.