JP2004125536A - Metal gasket and radioactive substance containment vessel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent reduction of contact pressure of sealing by a metal gasket, and to improve sealing performance. <P>SOLUTION: This metal gasket 20 is a double ring type metal gasket what is called wherein two springs 30a, 30b having different hoop diameters Df are concentrically disposed and are combined while covering two sides with an outer cover 40. The spring 30 is shaped from a plate material in a nearly circular plate curl state such that a part S of the plate material is overlapped, and the overlapped portion S is slid by compression in the sealing to wholly reduce a diameter of the spring 30. That is, because the diameter of the spring 30 is only reduced, increase of a contact face by the spring 30 is suppressed to prevent the reduction of the contact pressure per unit area. Accordingly, the certain sealing becomes possible. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a metal gasket and a radioactive material storage container used for sealing a cask or the like that stores a recycled fuel assembly.
[Prior art]
[0002]
A nuclear fuel assembly that has finished burning at the end of the nuclear fuel cycle is called a recycled fuel assembly. Since the recycled fuel assembly contains a high radioactive material such as FP, it needs to be thermally cooled, and is cooled for a long time in a cooling pit of a nuclear power plant. Then, it is stored in a cask which is a shielding container, transported to a reprocessing facility by a truck or the like, and stored. Since the cask contains a highly radioactive substance, strict caution is required to seal the cask during the storage period in which 40 to 60 years are expected.
[0003]
FIG. 6 is a sectional view showing the structure of a conventional cask. FIG. 7 is a partially enlarged view of the cask shown in FIG. The cask 500 includes a body 501 made of stainless steel or carbon steel, an outer cylinder 502 constituting an outer surface of the cask, and a resin material of a polymer material containing hydrogen filled between the body 501 and the outer cylinder 502. 503, a bottom plate 505 welded to the lower part of the trunk body 501 and enclosing a resin 504, and a primary lid 507 and a secondary lid 508 provided on a flange 506 welded and integrated with the trunk body 501. . The basket 513 for storing the recycled fuel assembly is arranged in the cavity 509 of the trunk body 501. The primary lid 507 and the secondary lid 508 are fixed to the flange 506 by bolts 510 and 511, and a resin 512 is sealed in the secondary lid 508.
[0004]
The basket 513 includes a plurality of cells formed of a composite material of boron (B) and aluminum. The cavity 509 of the cask 500 is filled with helium gas in a negative pressure state. On the other hand, the inside of the gap between the primary lid 507 and the secondary lid 508 has a positive pressure, thereby forming a pressure barrier between the inside and the outside of the cask 500. The secondary lid 508 is provided with a hole 514 for measuring the pressure in the space between the lids, and a pressure sensor 515 is provided at the outlet of the hole 514.
[0005]
The primary cover 507 is provided with a valve 516 for replacing gas in the cask 500, and the valve 516 is covered by a valve cover 517. Sealing between the primary lid 507 and the trunk body 501 and between the secondary lid 508 and the trunk body 501 have heat resistance, corrosion resistance, and high durability from the viewpoint of maintaining the sealing function for a long period of time. Metal gaskets 518 and 519 are used.
[0006]
FIG. 8 is an enlarged view showing a metal gasket used for sealing a cask and a sealing portion of the cask. The seal between the primary lid 507 and the trunk bodies 501 and 506 and between the secondary lid 508 and the trunk bodies 501 and 506 have the same seal structure. The gasket groove 525 is formed by machining, and the metal gaskets 518 and 519 used have a double ring structure. The metal gaskets 518 and 519 cover a coil spring 521 made of Inconel (trade name: nickel-based alloy) that is resistant to corrosion and high-temperature oxidation with an inner jacket 522 also made of Inconel, and further, an outer jacket 523 made of aluminum. And the inner and outer rings are collectively covered by FIG. 8A shows a state before using the metal gasket 518 (519). When the secondary lid 508 and the like and the trunk body 501 and the like are fixed, the metal gasket 518 (519) is deformed as shown in FIG. 8B by the tightening force and exhibits a sealing function.
[0007]
The gasket groove 525 is fixed using bolt holes provided in the outer cover 523. As the metal gaskets 518 and 519, for example, "Triback" manufactured by Nippon Valqua Industries, Ltd. or "Helico Flex Seal" manufactured by CEFILAC of France, which is often used for nuclear cask, can be used. In addition to this, there is also known a metal gasket in which an outer skin is provided on a spring formed by shaping a comb-shaped rectangular plate material into a plate shape as described in Patent Document 1 below.
[0008]
[Patent Document 1]
JP-A-11-63269 P4-5 FIG.
[0009]
In the case of the metal gasket 518 (519) using the coil spring 521, when crushed at the time of sealing, the inner coil spring 521 deforms elliptically, the radius of curvature increases, the contact area increases, and the contact pressure per unit area increases. Decrease. As a result, the sealing performance of the metal gasket 518 (519) may be reduced. On the other hand, according to the metal gasket described in Patent Literature 1, the overlapping portion of the spring slides, and the cross-sectional radius of the spring decreases. Thereby, an increase in the contact area can be prevented, and an appropriate contact pressure can be maintained.
[0010]
[Problems to be solved by the invention]
However, since the metal gasket described in Patent Document 1 has a single ring structure, there is a problem that its sealing performance is insufficient when applied to a cask or the like that stores a recycled fuel assembly. When a double ring-shaped metal gasket 518 (519) using the coil spring 521 is used to enhance the sealing performance, the contact pressure per unit area is reduced as described above, and the sealing performance becomes insufficient. There is a problem.
[0011]
Therefore, the present invention has been made in view of the above, and an object of the present invention is to provide a metal gasket and a radioactive substance storage container which can prevent a reduction in contact pressure of a seal by a metal gasket and can improve sealing performance. .
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a metal gasket according to the present invention has a cavity inside a cavity interposed between a trunk body of a radioactive substance storage container for storing a recycled fuel assembly and a lid attached to a cavity opening of the trunk body. The metal gasket has a substantially circular plate winding shape having a partially overlapping portion and two ring-shaped springs having different hoop diameters are arranged concentrically, and the metal gasket is arranged in a concentric manner. Is covered with a jacket, and the rings are connected to each other with the jacket to be integrated.
[0013]
When a substantially circular plate-shaped spring is pressurized during sealing, the springs slide on each other at the overlapping portion, and have a smaller diameter as a whole. For this reason, an increase in the contact area between the jacket and the sealing surface is suppressed, and a decrease in the contact pressure can be prevented. In addition, the double ring structure enhances the sealing performance. In addition, the substantially circular plate-winding shape having a part that overlaps with the above part means that the plate material is wound and its ends overlap, and the cross-section is generally circular (the same applies hereinafter). .
[0014]
The metal gasket according to the next invention is a metal gasket which maintains a hermetically sealed cavity by being interposed between a trunk body of a radioactive substance storage container for storing a recycled fuel assembly and a lid attached to a cavity opening of the trunk body. The metal gasket has a substantially circular plate winding shape having a part where the cross-sectional shape partially overlaps, and two concentrically arranged ring-shaped springs having irregularities on the surface and having different hoop diameters are arranged concentrically. A double ring is formed by coating with the inner jacket, and further, the outer jacket is coated on the inner jacket, and the rings are connected and integrated by the outer jacket, and the inner jacket is made of a material harder than the outer jacket. It is characterized by becoming.
[0015]
When the surface of the spring has irregularities, for example, the spring bends a comb-like plate material into a circular cross section, or forms a wire to form a substantially circular plate having a portion where the cross sectional shape substantially overlaps. In this case, the outer cover is made of a relatively soft material in order to ensure the sealing property, so that unevenness of the spring causes variation in the contact pressure on the sealing surface. In such a case, the reliability of the seal is impaired, but if the spring is covered with an inner jacket made of a material harder than the outer jacket and then the outer jacket is coated thereon, the influence of the irregularities Is canceled by the inner jacket, and as a result, a uniform pressure is applied to the outer jacket through the inner jacket. Thereby, the contact pressure can be made uniform and the sealing performance can be improved.
[0016]
The radioactive substance storage container according to the next invention is characterized in that the metal gasket is interposed between a body of a cask for storing a recycled fuel assembly and a lid attached to a cavity opening of the body.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings. It should be noted that the present invention is not limited by the embodiment. In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or those that are substantially the same. The application range of the metal gasket according to the present invention is not particularly limited, and may be applied to, for example, a seal of a cask, a seal portion of a containment vessel, and the like. In addition, this metal gasket is particularly suitable for applications that maintain hermetic performance in a relatively high temperature environment for a period of several decades, among which a recycled fuel assembly is stored, transported, and stored for a long time. Suitable for cask.
[0018]
(Embodiment 1)
FIG. 1 is an explanatory diagram showing a seal structure in a cask according to Embodiment 1 of the present invention. In the cask seal structure 10, the metal gasket 20 is of a so-called double ring type in which two springs 30a and 30b having different hoop diameters Df are arranged concentrically and are joined while being covered with a jacket 40. Things. That is, in the metal gasket 20, the inner race 70 and the outer race 80 are integrated by the flat portion 40 c of the outer skin 40.
[0019]
The seal structure 10 is provided, for example, between the secondary lid 508 of the cask 500 and the flange of the body 501. The seal structure and the metal gasket according to the present invention can be applied between the primary cover of the cask and the body 501 (the same applies hereinafter). The spring 30 is formed in a substantially circular plate winding shape so that a portion S is overlapped from a plate material, and the overlapping portion S slides due to compression at the time of sealing, so that the diameter of the spring 30 is reduced as a whole. That is, since only the diameter of the spring 30 is reduced, an increase in the contact surface by the spring 30 is suppressed, and a decrease in the contact pressure per unit area can be prevented. For this reason, reliable sealing becomes possible.
[0020]
Also, a number of drain holes 101 may be formed in the circumferential direction inside the spring 30b. The drain hole 101 is for letting out water that has entered inside to the outside, and its position is radially inward and substantially at the center in the thickness direction (height direction in the figure). For example, if it is provided below, it interferes with the jacket 40, so that it is necessary to perform perforation processing also on the jacket 40. In addition, if it is provided near the seal surface 90, water easily enters between the outer cover 40 and the seal surface 90, and it becomes difficult to drain water. Specifically, the position of the drain hole 101 is preferably within ± 45 ° with respect to the radially inner line L. On the other hand, in the small-diameter spring 30a, since the overlapping portion S is located inside the metal gasket, it is necessary to drill the drainage hole 101 at a position where the overlapping portion S is not slid and hidden by compression during sealing. .
[0021]
As a material of the outer cover 40, a soft metal such as aluminum, silver, copper, or nickel is used to secure sealing performance. The spring 30 is made of a nickel-based alloy such as Inconel (registered trademark) or stainless steel that is resistant to corrosion and high-temperature oxidation so that the spring 30 can maintain its elasticity even in a high-temperature environment. When it is desired to improve the durability at a higher temperature, Nimonic (registered trademark) having a high Co content may be used.
[0022]
For the secondary lid 508, the primary lid, and the body 501, stainless steel or carbon steel is used to shield radiation and maintain mechanical strength. On the other hand, a soft metal such as aluminum or silver is used for the outer cover 40 of the metal gasket 20 in order to exhibit sealing performance. For this reason, a potential difference is generated between the two by the contact of the dissimilar metals, which causes electrolytic corrosion of the metal gasket 20 and causes sealing leakage. For this reason, SUS317 or SUS625 containing molybdenum is used as the material of the secondary lid 508 and the body 501 of the cask to prevent electrolytic corrosion.
[0023]
Further, SUS317 or SUS625 is excellent in weldability, and therefore is suitable for a material having a large number of welds, such as a cask. Further, in addition to SUS317 and SUS625, SUS314, SUS316, SUS326, SUS345, and the like can be used. Further, the seal surface 90 may be formed by applying a buildup of the same material without using SUS317 or the like for the secondary lid 508 and the trunk body 501 (not shown).
[0024]
Further, aluminum having a higher corrosion potential than SUS317 or SUS625 containing molybdenum used as a material of the secondary lid 508 and the body 501 of the cask may be used as the jacket 40. By doing so, the outer cover 40 of the metal gasket 20 that is easier to replace than the secondary lid 508 and the trunk body 501 is more likely to be corroded, so that the secondary lid 508 and the trunk body 501 are protected from electrolytic corrosion. .
[0025]
In addition, in the said embodiment, the position of the hole of the inner cover 40 is pierced toward the radial inside (line L connecting the center of two rings), when it is supposed that it faces diagonally downward. In particular, when the drain hole 101 is drilled through the inner jacket 40 and the outer jacket 50, water easily penetrates between the outer jacket 50 and the sealing surface 90b, which makes it difficult to drain water. It is. In addition, it is because processing of the jacket 50 may be required. Specifically, the position of the drain hole 101 is preferably within ± 45 °, more preferably within ± 20 °, about the inward line L.
[0026]
Note that gold or silver plating may be applied to the former side and zinc plating may be applied to the latter side between the helium side (cavity side) and the atmosphere or rain side with respect to the metal gasket. Further, plating of copper, nickel, or the like may be performed near the center.
[0027]
According to the seal structure 10 and the metal gasket 20 described above, a decrease in the contact pressure per unit area with respect to the seal surface 90 can be prevented, and the sealability can be significantly improved by the double ring. Particularly, it is suitable for sealing a container for storing a radioactive substance such as a cask.
[0028]
(Embodiment 2)
FIG. 2 is an explanatory view showing a seal structure in a cask according to Embodiment 2 of the present invention. In the seal structure 11, the metal gasket 21 is formed by bending an inner jacket 31 having a spring function and an outer jacket 41 laminated on the inner jacket 31. In order to manufacture the metal gasket 21, first, the plate-shaped inner cover 31 and the outer cover 41 are laminated, joined by diffusion bonding or the like, and bent into a shape as shown in FIG. Specifically, both sides of the inner cover 31 and the outer cover 41 are bent into a substantially circular plate winding shape, and a partially overlapping portion S is formed. The inner ring 71 includes an inner cover 31a and an outer cover 41a, and the outer ring 81 includes an inner cover 31b and an outer cover 41b. The inner ring 71 and the outer ring 81 are connected by the flat portions 31c and 41c.
[0029]
As a material of the outer cover 41, a soft metal such as aluminum, silver, copper, or nickel is used to secure sealing performance. The inner cover 31 is made of a nickel-based alloy, such as Inconel (registered trademark), which is resistant to corrosion and high-temperature oxidation, so that elasticity can be maintained even in a high-temperature environment. When it is desired to improve the durability at a higher temperature, Nimonic (registered trademark) having a high Co content may be used.
[0030]
The metal gasket 21 is interposed between the secondary lid 508 and the body 501 to seal the inside. In the sealed state, the inner ring 71 and the outer ring 81 are brought into contact with the sealing surfaces 90a, 90b at a predetermined pressure by the outer cover 41 thereof. The metal gasket 21 is compressed in the vertical direction in a sealed state, but the overlapping portion S slides, and the diameter of the inner and outer rings 71 and 81 is reduced as a whole. That is, since the diameters of the inner and outer rings 71 and 81 functioning as springs only decrease, the contact surface between the outer cover 41 and the seal surface 90 does not increase. As a result, a reduction in contact pressure due to the metal gasket 21 is prevented, and sealing can be reliably performed. In addition, since it has a double ring structure, it is suitable for products requiring high confidentiality such as casks.
[0031]
(Embodiment 3)
FIG. 3 is an explanatory view showing a seal structure in a cask according to Embodiment 3 of the present invention. FIG. 4 is an explanatory diagram showing a method of manufacturing the spring shown in FIG. FIG. 5 is an explanatory diagram showing a sealed state by the metal gasket of FIG. In this seal structure 12, the metal gasket 22 includes two springs 32 a and 32 b having different hoop diameters Df arranged concentrically, and covers the inner covers 42 a and 42 b, and covers both of them with the outer cover 52. It is of the so-called double ring type that combines while being connected. That is, the metal gasket 22 has a configuration in which the inner ring 72 and the outer ring 82 are collectively covered by the outer cover 52, and the inner ring 72 and the outer ring 82 are integrated by the flat portion 52 c of the outer skin 52. The inner ring 72 includes a spring 32a, an inner cover 42a, and an outer cover 52a, and the outer ring 82 includes a spring 32b, an inner cover 42b, and an outer cover 52b.
[0032]
The seal structure 12 is provided, for example, between the secondary lid 508 of the cask 500 and the flange of the body 501. The seal structure and the metal gasket according to the present invention can of course be applied between the primary lid of the cask 500 and the body 501. The spring 32 is formed in a substantially circular plate winding shape so that a part S is overlapped from a plate material, and the overlapping part S slides due to compression at the time of sealing, and the diameter of the spring 32 is reduced as a whole. That is, since only the diameter of the spring 32 is reduced, it is possible to suppress an increase in the contact surface of the spring 32 and prevent a decrease in contact pressure per unit area. For this reason, reliable sealing becomes possible.
[0033]
The outer cover 52 is made of a soft metal such as aluminum, silver, copper, nickel or the like, and secures sealing performance. The inner cover 42 and the spring 32 are made of a nickel-based alloy such as Inconel (registered trademark) or stainless steel, which is resistant to corrosion and high-temperature oxidation, so that elasticity can be maintained even in a high-temperature environment. When it is desired to improve the durability at a higher temperature, Nimonic (registered trademark) having a high Co content may be used.
[0034]
As shown in FIG. 4A, the spring 32 has a rectangular strip-shaped plate having one end in the longitudinal direction as a base 301 and a large number of slits 303 formed at the other end to form a large number of comb teeth 302. This plate is bent into a substantially circular plate winding shape around the direction indicated by the dashed line in the figure, thereby forming a ring-shaped spring 32 having a plate winding cross section as shown in FIG. The base portion 301 becomes an overlapping portion S on the spring 32 bent in this way, and can slide on the comb teeth 303.
[0035]
Since the surface of the spring 32 has slits like comb teeth, if sealing is performed only through the outer cover 52 made of a soft metal, the outer cover 52 enters the slit 302 and the sealing surface 90 Fluctuations in pressure occur. For this reason, as shown in FIG. 5, an inner jacket 42 made of a thin hard metal is interposed between the outer jacket 52 and the spring 32, and the inner jacket 42 is once pushed by the comb teeth 303 of the spring 32, and the inner jacket 42 is pressed. If the jacket 52 is pressed by the button 42, pressure can be uniformly and entirely applied to the jacket 52. Thereby, the outer cover 52 comes into contact with the sealing surface 90 with a uniform contact pressure, so that reliable sealing can be achieved.
[0036]
For the secondary lid 508, the primary lid, and the body 501, stainless steel or carbon steel is used to shield radiation and maintain mechanical strength. On the other hand, a soft metal such as aluminum or silver is used for the outer cover 52 of the metal gasket 22 in order to exhibit sealing performance. For this reason, a potential difference is generated between the two by the contact of the dissimilar metals, which causes electrolytic corrosion of the metal gasket 22 and causes sealing leakage. For this reason, SUS317 or SUS625 containing molybdenum is used as the material of the secondary lid 508 and the body 501 of the cask to prevent electrolytic corrosion.
[0037]
Further, SUS317 or SUS625 is excellent in weldability, and therefore is suitable for a material having a large number of welds, such as a cask. Further, in addition to SUS317 and SUS625, SUS314, SUS316, SUS326, SUS345, and the like can be used. Further, the seal surface 90 may be formed by applying a buildup of the same material without using SUS317 or the like for the secondary lid 508 and the trunk body 501 (not shown).
[0038]
Further, aluminum having a higher corrosion potential than SUS317 or SUS625 containing molybdenum used as a material of the secondary lid 508 and the body 501 of the cask may be used as the jacket 52. In this way, the outer cover 52 of the metal gasket 22 that is easier to replace than the secondary lid 508 and the trunk body 501 is more likely to be corroded, so that the secondary lid 508 and the trunk body 501 are protected from electrolytic corrosion. .
[0039]
【The invention's effect】
As described above, according to the present invention, moisture in the metal gasket can be removed and sufficient sealing performance can be exhibited for a long period of time.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a cask sealing structure according to Embodiment 1 of the present invention.
FIG. 2 is an explanatory view showing a seal structure of a cask according to Embodiment 2 of the present invention.
FIG. 3 is an explanatory view showing a seal structure of a cask according to Embodiment 3 of the present invention.
FIG. 4 is an explanatory view showing a method of manufacturing the spring shown in FIG.
FIG. 5 is an explanatory view showing a sealed state by the metal gasket of FIG. 3;
FIG. 6 is a sectional view showing the structure of a conventional cask.
FIG. 7 is a partially enlarged view of the cask shown in FIG. 6;
FIG. 8 is an enlarged view showing a metal gasket used for sealing a cask and a sealing portion of the cask.
[Explanation of symbols]
Reference Signs List 10 seal structure 20 metal gasket 30 spring 40 jacket 90 sealing surface

Claims (3)

A metal gasket for maintaining a hermetic seal in a cavity by being interposed between a trunk body of a radioactive substance storage container for storing a recycled fuel assembly and a lid attached to a cavity opening of the trunk body,
The metal gasket has a substantially circular plate-winding shape having a partially overlapping portion and two ring-shaped springs having different hoop diameters are arranged concentrically, and each of the springs is covered with a jacket to cover the outside. A metal gasket, wherein rings are connected to each other by a cover to be integrated. A metal gasket for maintaining a hermetic seal in a cavity by being interposed between a trunk body of a radioactive substance storage container for storing a recycled fuel assembly and a lid attached to a cavity opening of the trunk body,
The metal gasket has a substantially circular plate winding shape having a partially overlapped cross-sectional shape, and has two ring-shaped springs having concavities and convexities on the surface and having different hoop diameters concentrically arranged, and the respective springs are placed inside. Forming a double ring by covering with a cover, further covering the inner cover on the inner cover and connecting and integrating the rings by the outer cover,
A metal gasket, wherein the inner cover is made of a material harder than the outer cover. 3. A radioactive substance storage container characterized in that the metal gasket according to claim 1 or 2 is interposed between a body of a cask for housing a recycled fuel assembly and a lid attached to a cavity opening of the body.

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