JP3986249B2 - Cask sealing method and cask - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a cask sealing method and a cask, which is a pressure vessel that accommodates a spent fuel assembly that has finished burning, is emergency and effective against leaks, and can eliminate the work of replacing a metal gasket.
[0002]
[Prior art]
FIG. 5 is a cross-sectional view showing the structure of a conventional cask. FIG. 6 is a partially enlarged view of the cask shown in FIG. This cask 500 is made of a stainless steel or carbon steel body 501, an outer cylinder 502 constituting the outer surface of the cask, and a polymer material resin containing hydrogen filled between the body 501 and the outer cylinder 502. 503, a bottom plate 505 having a structure in which a resin 504 is sealed and welded to a lower portion of the trunk body 501, and a primary lid 507 and a secondary lid 508 provided on a flange portion 506 integrally welded to the trunk body 501. . The basket 513 that stores the spent fuel assembly is disposed in the cavity 509 of the trunk body 501. As shown in FIG. 6, the primary lid 507 and the secondary lid 508 are fixed to the flange portion 506 by bolts 510 and 511, and a resin 512 is sealed in the secondary lid 508.
[0003]
The basket 513 is composed of 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 space between the primary lid 507 and the secondary lid 508 has a positive pressure. A pressure barrier is formed between them. 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.
[0004]
The primary lid 507 is provided with a valve 516 for replacing gas in the cask, and the valve 516 is covered with 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 has heat resistance, corrosion resistance, and high durability from the viewpoint of maintaining a sealing function for a long period of time. Metal gaskets 518 and 519 are used.
[0005]
FIG. 7 is an enlarged view showing a seal portion of the cask. The seal portions between the primary lid 507 and the trunk body 501 and between the secondary lid 508 and the trunk body 501 have the same seal structure. The gasket groove 520 is formed by machining, and the metal gaskets 518 and 519 to be used have a double ring structure. These metal gaskets 518 and 519 are coated with a coil spring 521 made of Inconel (trade name: nickel-based alloy containing 16% chromium and 7% iron) resistant to corrosion and high-temperature oxidation, and also coated with Inconel endothelium 522. Further, the inner and outer rings are collectively covered with an aluminum outer skin 523.
[0006]
The gasket groove 520 is fixed using a bolt hole provided in the outer skin 523 portion. As the metal gaskets 518 and 519, for example, “Triback” manufactured by Nippon Valqua Industries Co., Ltd., “Helicoflex Seal” manufactured by CEFILAC of France, etc., which have many uses for nuclear casks, can be used.
[0007]
The temperature and time dependence of plastic deformation rate and sealing performance of metal gaskets can be expressed by Larson-Miller Parameter (LMP). For details, see “Development of evaluation method for long-term sealing performance of spent fuel storage cask”. (Kato, Ito, Saegusa, Journal of the Atomic Energy Society of Japan, Vol. 38, No. 6, 95-101, 1996). In general, the long-term sealing performance of a metal gasket is performed by obtaining the LMP of the sealing retention limit and predicting the limit time at a predetermined temperature.
[0008]
Further, O-ring grooves 524 into which synthetic rubber O-rings are fitted are machined on the inner peripheral sides of the metal gaskets 518 and 519. Normally, when the cask 500 is stored, an O-ring made of synthetic rubber is not used. The reason for not using an O-ring made of synthetic rubber during storage is that it cannot withstand use under high temperature (around 150 ° C.) and high dose conditions.
[0009]
[Problems to be solved by the invention]
On the other hand, the metal gaskets 518 and 519 are unsuitable for use during cask transportation for the following reasons. When the metal gaskets 518 and 519 are used, the amount of deviation between the secondary lid 508 and the trunk body 501 with respect to the leakage rate (1 × 10 ⁻⁹ Pa · m ³ / s) which is the manufacturer's recommended value is 0.2 mm to 0. Although the limit is about 3 mm, the amount of deviation when the cask 500 actually falls is several mm, and both are different by almost one digit. Therefore, when the cask 500 fitted with the metal gaskets 518 and 519 falls, the recommended value may be exceeded. For this reason, in the conventional cask 500, the metal gasket 518 of the secondary lid 508 is made of synthetic rubber during transportation. It was necessary to carry out cask transport after replacing the O-ring. On the other hand, it is confirmed that the synthetic rubber O-ring can maintain a sufficient sealing function against lateral slippage due to dropping if it is several months (transportation period) even at high temperatures and high doses. ing.
[0010]
However, in order to replace the metal gasket 518 and the synthetic rubber O-ring, it is necessary to first remove the secondary lid 508 and attach the O-ring to the O-ring groove 524 of the secondary lid 508. Then, the secondary lid 508 is attached to the cask again, and then the confidentiality inspection is performed. Moreover, since these operations are all performed under a high dose, the cask 500 must be performed in a state where it is submerged in the pool. Alternatively, the cask 500 must be installed in a hot cell surrounded by a thick shielding wall and performed by remote work. For this reason, the conventional cask 500 has a problem that it takes time and cost to replace the seal.
[0011]
Further, the metal gasket 518 may be leaked due to a decrease in contact surface pressure due to plastic flow occurring in the outer skin 523 as a result of a predetermined tightening force acting at a high temperature. Since the internal gas leak is detected by the pressure sensor 515 between the lids, for example, when a leak occurs, some effective sealing work is required. However, research and development to improve the sealing function so that leaks do not occur anyway has been conducted in the past, and there is no method for performing emergency and effective sealing work regardless of whether the cask is being stored or transported. It was.
[0012]
Accordingly, the present invention has been made in view of the above, and a first object thereof is to provide an emergency and effective cask sealing method and cask against a leak. It is a second object of the present invention to provide a cask sealing method and a cask that can be transported using only a metal gasket while omitting a metal gasket replacement operation.
[0013]
[Means for Solving the Problems]
In order to achieve the above-described object, a cask sealing method according to claim 1 is a basket in which a cavity with a bottom is formed in a trunk body for shielding gamma rays, and a spent fuel assembly is accommodated in the cavity. A cask sealing method in which a lid is attached to the cavity opening side of the trunk body, and a metal gasket is provided between an end of the trunk body and a peripheral edge of the lid to maintain a seal in the cavity. An introduction hole communicating from the outside is provided in the gasket groove into which the metal gasket is inserted. When the sealing performance of the metal gasket is deteriorated, a rubber material is introduced from the introduction hole and the rubber material is vulcanized in the gasket groove. It is characterized by doing so.
[0014]
For example, when the metal gasket is laterally displaced when it is dropped during cask transportation and a sealing failure occurs, a rubber material is introduced from the introduction hole and vulcanized and molded inside. Since the inside of the gasket groove is generally sealed with a metal gasket, the introduced rubber material is filled only in the sealed compartment. Thereby, a new sealing boundary is formed in the gasket groove, and the sealing performance can be recovered quickly and effectively in an emergency.
[0015]
The introduction hole may be a leak inspection introduction hole already provided for leak inspection, or may be provided by machining a lid separately. Further, the communication destination of the introduction hole may be all or a part of the seal section formed by the metal gasket. The rubber material may be either a heat vulcanization type or a room temperature vulcanization type. If ready to carry out such a sealing method, the cask can be transported without replacing the metal gasket with a rubber O-ring. Note that this method is effective not only during cask transport but also when plastic flow or the like occurs due to long-term use of the cask and the sealing by the metal gasket is broken.
[0016]
The cask sealing method according to claim 2 is characterized in that, in the cask sealing method, the rubber material is further pressure-filled. By pressure-filling the rubber material, the rubber material can be uniformly distributed in the gasket groove, and a sealing boundary can be reliably formed over the entire circumference. For this reason, the cask sealing performance can be restored effectively and reliably. The pressure filling of the rubber material can be easily performed by a pump.
[0017]
According to a third aspect of the present invention, there is provided a cask sealing method in which a bottomed cavity is formed in a trunk body that shields γ rays, and a basket for storing spent fuel assemblies is housed in the cavity. In the cask sealing method in which a lid is attached to the cavity opening side and a metal gasket is provided between the end of the trunk body and the peripheral edge of the lid to hold the seal in the cavity, the gasket for inserting the metal gasket An introduction hole communicating from the outside is provided in the groove, and when the sealing performance by the metal gasket is deteriorated, an adhesive is introduced from the introduction hole, and the adhesive is cured in the gasket groove. .
[0018]
By using the adhesive, great adhesion can be obtained to the outer surface of the metal gasket or the sealing surface, so that the sealing performance can be recovered quickly and effectively in an emergency.
[0019]
According to a fourth aspect of the present invention, there is provided a cask having a bottomed cavity formed in a trunk body that shields gamma rays, and a basket for storing spent fuel assemblies is accommodated in the cavity. In a cask that holds a seal in the cavity by providing a metal gasket between the end of the trunk body and the peripheral edge of the lid, the lid communicates from the outside into the gasket groove into which the metal gasket is inserted. In addition, an introduction hole for introducing a rubber material and a sealing member for sealing the introduction hole are provided.
[0020]
This cask is suitable for carrying out the above-mentioned sealing method, and the sealing performance of the cask is quickly and effectively restored in the gasket groove of the communication destination by introducing the rubber material from the introduction hole for introducing the rubber material. Can do. Further, the metal gasket can be transported without being replaced with a rubber O-ring. After the rubber material is introduced, it is sealed with the sealing member. In particular, when the introduced rubber material is vulcanized, if the sealing member is sealed, the inside of the gasket groove is in a pressurized state due to thermal expansion, so that the sealing can be surely performed. In addition, it is preferable to provide a plurality of introduction holes for introducing the rubber material from the viewpoint of degassing during introduction. Further, the communication destination of the introduction hole for introducing the rubber material may be the radial center in the gasket groove or both ends.
[0021]
The cask according to claim 5 is characterized in that, in the cask, a heating means is provided on the lid along the gasket groove. Vulcanized rubber is introduced into the gasket groove, and the vulcanized rubber is heated by heating means provided along the gasket groove. Power for heating is supplied from, for example, a transportation vehicle or a portable small generator.
[0022]
The cask according to claim 6 is characterized in that, in the cask, a leak inspection introduction hole communicating between the lid and the gasket groove is used as an introduction hole for introducing the rubber material. . There may be a leak inspection introduction hole for inspecting the sealing performance of the metal gasket, but this leakage inspection introduction hole communicates with the gasket groove from the outside, so the rubber material is introduced. It can also be used as an introduction hole.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.
[0024]
[Embodiment 1]
1 is a cross-sectional view showing a cask sealing structure according to Embodiment 1 of the present invention. The sealing structure 1 is provided, for example, between the secondary lid 508 of the cask 500 and the flange portion 506 of the trunk body 501. The metal gasket 2 has a configuration in which a ring-shaped coil spring 3 is covered with an inner skin 4 and inner and outer rings are collectively covered with an outer skin 5. The ring diameter of the metal gasket 2 is about 2 m, the cross-sectional diameters of the inner ring 7 and the outer ring 8 are about 5.5 mm, the thickness of the outer skin 5 is 0.4 mm, and the thickness of the inner skin 4 is 0.2 mm. A soft metal such as aluminum or silver is used for the material of the outer skin 5, and Inconel is used for the inner skin 4 and the coil spring 3.
[0025]
Further, an introduction hole 10 for introducing a rubber material is provided near the radial center of the gasket groove 9. The introduction hole 10 is formed in the secondary lid 508 by machining, and communicates the inside of the gasket groove 9 with the outside. A screw-type plug 12 is provided at the inlet 11 of the introduction hole 10. A plurality of the introduction holes 10 are provided, some of which function as gas vent holes when the rubber material is injected (not shown).
[0026]
Further, as shown in FIG. 2, conductive entry apertures 21 for introducing the rubber material may be processed and formed on the flange portion 506 of the barrel main body 501. In this way, since the outer skin 5 of the metal gasket 2 does not get in the way, the rubber material can be easily injected. Furthermore, as shown in FIG. 3, introduction holes 31 for introducing a rubber material may be provided in all the seal sections S1 to S3. In this way, the entire gasket groove 9 is sealed with the rubber material, so that the sealing performance can be sufficiently recovered. Further, the secondary lid 508 is provided with a leak inspection introduction hole (not shown) for inspecting the sealing performance of the metal gasket 2, and a rubber material can be injected using this introduction hole. .
[0027]
Returning to FIG. 1, the heater 13 is arranged along the metal gasket 2 on the upper surface of the secondary lid 508. The power source 14 of the heater 13 is connected to, for example, a power source of a truck 15 for transporting a cask or is connected to a portable small generator. Thus, if the heater 13 is provided in the secondary lid 508 of the cask, it is possible to take an emergency sealing measure even during the cask transportation. In addition, an electromagnetic coil etc. which generate | occur | produce a high frequency can also be used as a heating means (illustration omitted). According to the electromagnetic coil, the rubber material can be heated by Joule heat generated on the surface of the gasket groove 9.
[0028]
Normally, the cask maintains a predetermined sealing performance by the metal gasket 2, but for example, the cask may be dropped during transportation of the cask or may be plastically flowed in the metal gasket 2 due to long-term storage, thereby reducing the sealing performance. In such a case, an emergency leak prevention measure is required to prevent or minimize internal gas leakage. In this cask, the rubber material is injected from the introduction hole 10 through which the rubber material is introduced , and emergency measures are taken to restore the sealing. Whether or not the sealing performance has deteriorated is monitored by a pressure sensor (see FIG. 6) provided in the secondary lid 508, and the internal negative pressure can be maintained from the detection result. Judgment based on whether or not.
[0029]
The injected rubber material enters the gasket groove 9 through the introduction hole 10 for introducing the rubber material . The rubber material that has entered the gasket groove 9 enters the seal section S <b> 1 through the bolt hole 16 provided in the outer skin 5 of the metal gasket 2. On the other hand, due to the intrusion of the rubber material, the internal gas escapes to the outside from the introduction hole 10 for introducing another open rubber material . Since the seal section S1 is regulated by the seal boundary by the metal gasket 2, the rubber material does not break the seal section S1 and enter the gasket groove 9 on both sides. Next, when the rubber material is sufficiently injected, all the introduction holes 10 are sealed with plugs 12, and the rubber material is heated by the heater 13. As a result, the rubber material is vulcanized and thermally expanded, so that the pressure in the gasket groove rises, and the rubber material spreads throughout the gasket groove 9. As a result, a new sealing boundary is formed by the rubber material, and an emergency and effective and reliable sealing is obtained.
[0030]
Examples of the rubber material include nitrile rubber (NBR), butyl rubber, and ethylene propylene rubber. Further, a rubber material vulcanized at room temperature, such as urethane rubber, polybutadiene, or silicone, may be used. In this case, when injecting rubber, it is preferable to pressurize with a pump in advance. Further, the heater 13 is unnecessary when a room temperature vulcanized rubber material is used.
[0031]
Further, an adhesive may be introduced instead of the rubber material. The adhesive can be used ThreeBond Co., urethane and Shin-Etsu Chemical Co., Ltd., such as Nichias Corporation, those silicone over emissions systems such as Toray Silicone. Moreover, either a thermosetting type or a room temperature curing type may be used. If an adhesive is used, there is no need for high-pressure injection, and the adhesive is bonded to the outer skin 5 and the sealing surface of the metal gasket 2, so that there is an advantage that a non-bonding interface does not occur as in the case of using a normal rubber material. For this reason, a new sealing boundary is formed by the adhesive, and the sealing function of the cask can be quickly and effectively restored.
[0032]
[Embodiment 2]
FIG. 4 is a sectional view showing a cask sealing structure according to Embodiment 4 of the present invention. In the cask sealing structure 40, the configuration of the first embodiment is applied to the metal gasket 42 provided between the primary lid 507 and the flange portion 506 of the trunk body 501. The flange portion 506 has an introduction hole 43 through which a rubber material is introduced from its side surface, and a screw-type plug 45 is provided at the inlet 44 of the introduction hole 43 through which the rubber material is introduced . Since the outlet 46 of the introduction hole 43 for introducing the rubber material is opened below the metal gasket 42, it is easy to inject the rubber material into the seal section S1. The rubber material used between the primary lid 507 and the flange portion 506 of the trunk body 501 is preferably vulcanized at room temperature because it is difficult to heat from the outside. Note that even a rubber material vulcanized by heating can be vulcanized by decay heat because the part is close to the inside of the cask. For this reason, the room temperature vulcanization mold and the heat vulcanization mold can be selected based on the temperature in the cask.
[0033]
Sealing between the primary lid 507 and the flange portion 506 of the trunk body 501 may cause a sealing failure due to a lateral shift of the metal gasket 42 during cask transportation or plastic flow during long-term storage. A new sealing boundary is created in the gasket groove 47 by injecting the rubber material into the gasket groove 47 from the introduction hole 43 for introducing the rubber material and curing it. For this reason, the sealing function of the cask can be recovered quickly and effectively. In particular, if treatment is performed together with the sealing structure 1 between the secondary lid 508 and the flange portion 506 of the trunk body 501, internal gas leakage can be reliably prevented.
[0034]
【Example】
The conditions of the cask to be implemented are as follows. Under these conditions, the following rubber material or adhesive is injected into the gasket groove.
(1) Cask conditions (1) Applicable site Both primary and secondary lid gasket grooves are both made of stainless steel (SUS304) (2) Operating temperature: Maximum 130 ° C (during long-term storage of cask)
Radiation: 2 mSv / H or less (3) Metal gasket Nihon VALQUA INDUSTRY CO., LTD. Tryback (2) Rubber material Creseal (Nissei Kogyo Co., Ltd.)
(3) Adhesive KE45 or KE40RTV (deoxime type: manufactured by Shin-Etsu Chemical Co., Ltd.)
[0035]
【The invention's effect】
As described above, in the cask sealing method of the present invention (Claim 1), an introduction hole communicating from the outside is provided in the gasket groove into which the metal gasket is inserted, and when the sealing performance by the metal gasket is lowered, Since the rubber material is introduced and the rubber material is vulcanized in the gasket groove, the sealing performance can be recovered quickly and effectively in an emergency. Further, the cask can be transported without replacing the metal gasket with a rubber O-ring.
[0036]
Further, in the cask sealing method of the present invention (claim 2), since the rubber material is pressurized and filled, the recovery of the cask sealing performance can be performed effectively and reliably.
[0037]
In the cask sealing method of the present invention (Claim 3), an introduction hole communicating from the outside is provided in the gasket groove into which the metal gasket is inserted, and when the sealing performance by the metal gasket is deteriorated, the adhesive is removed from the introduction hole. Since the adhesive is introduced and cured in the gasket groove, the sealing performance can be recovered quickly and effectively in an emergency. Further, the cask can be transported without replacing the metal gasket with a rubber O-ring.
[0038]
In the cask of the present invention (Claim 4), an introduction hole for introducing a rubber material communicating from the outside into a gasket groove for inserting a metal gasket and a sealing member for sealing the introduction hole for introducing the rubber material are provided. As a result, the sealing performance of the cask can be quickly and effectively restored.
[0039]
Moreover, in the cask of the present invention (Claim 5), the cask is provided with heating means, so that it is possible to respond immediately in case of emergency of leak occurrence.
[0040]
Moreover, in the cask of the present invention (Claim 6), the leak inspection introduction hole communicating between the lid and the gasket groove is used as the introduction hole for introducing the rubber material, so that the structure of the cask can be simplified. .
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a cask sealing structure according to Embodiment 1 of the present invention;
FIG. 2 is a cross-sectional view showing a modification of the sealing structure shown in FIG.
FIG. 3 is a cross-sectional view showing a modification of the sealing structure shown in FIG.
FIG. 4 is a cross-sectional view showing a cask sealing structure according to a second embodiment of the present invention.
FIG. 5 is a cross-sectional view showing the structure of a conventional cask.
6 is a partially enlarged view of the cask shown in FIG. 5. FIG.
FIG. 7 is an enlarged view showing a seal portion of a cask.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Sealing structure 2 Metal gasket 9 Gasket groove 10 Introduction hole 12 which introduces rubber material Plug 13 Heater 14 Power supply

Claims (6)

A cavity with a bottom is formed in the cylinder body for shielding gamma rays, a basket for storing spent fuel assemblies is stored in the cavity, and a lid is attached to the cavity opening side of the cylinder body. In a method for sealing a cask by providing a metal gasket between the end of the main body and the peripheral edge of the lid, and maintaining a seal in the cavity,
An introduction hole communicating from the outside is provided in the gasket groove for inserting the metal gasket. When the sealing performance of the metal gasket is deteriorated, a rubber material is introduced from the introduction hole, and the rubber material is vulcanized in the gasket groove. A cask sealing method characterized by the above.   The cask sealing method according to claim 1, further comprising pressurizing and filling the rubber material. A cavity with a bottom is formed in the cylinder body for shielding gamma rays, a basket for storing spent fuel assemblies is stored in the cavity, and a lid is attached to the cavity opening side of the cylinder body. In a method for sealing a cask by providing a metal gasket between the end of the main body and the peripheral edge of the lid, and maintaining a seal in the cavity,
An introduction hole communicating from the outside is provided in the gasket groove for inserting the metal gasket, and when the sealing performance of the metal gasket is deteriorated, an adhesive is introduced from the introduction hole, and the adhesive is cured in the gasket groove. A cask sealing method characterized by the above. A cavity with a bottom is formed in the cylinder body for shielding gamma rays, a basket for storing spent fuel assemblies is stored in the cavity, and a lid is attached to the cavity opening side of the cylinder body. In a cask that provides a metal gasket between the end of the main body and the peripheral edge of the lid to hold the seal in the cavity,
A cask characterized in that an introduction hole for introducing a rubber material and a sealing member for sealing the introduction hole are provided in the gasket groove for inserting the metal gasket from the outside.   The cask according to claim 4, further comprising heating means for the lid along the gasket groove. 6. The cask according to claim 4 , wherein a leak inspection introduction hole communicating between the lid and the gasket groove is used as an introduction hole for introducing the rubber material .

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