JP2020126084A - Cask manufacturing method - Google Patents

Abstract

To soften impacts to be applied to a cask structure and a stored object upon a cask falling.SOLUTION: A manufacturing method of a cask 1 comprises the steps of: preparing an internal buffer part 13 in which a thickness in a longitudinal direction is larger than a distance in a longitudinal direction between end surfaces in a longitudinal direction of a basket 7 and end surfaces of caster lid parts 22 and 23; and attaching the cask lid parts 22 and 23 to a cask bilge part 21 in a state with the internal buffer part 13 brought into contact with the end surface of the basket 7, thereby pushing the internal buffer part 13 against the end surface of the basket 7 to cause the internal buffer part to be subjected to plastic deformation, and causing one part of the internal buffer part 13 to protrude to an inside of a storage part 71 from the end surface of the basket 7. Accordingly, even if the cask 1 falls, a simple structure enables softening of a delayed falling impact caused by a collision of a stored object with an inner surface of the cask 1 delayed more than a collision of the cask 1 with a ground surface and the like.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method of manufacturing a cask capable of containing a fuel assembly.

Conventionally, spent fuel used in nuclear reactors, etc. is stored in a cooling pool inside a nuclear power plant until the radiation dose falls below a prescribed level, and then a cask with a shielding function and a sealing function etc. And will be transported to an intermediate storage facility or fuel reprocessing facility. Casks are required to maintain a predetermined shielding function and sealing function in the event of a fall accident during transportation.

Maintaining the function when the cask is dropped includes vertical drop in which the center axis of the cask falls in the vertical direction, horizontal drop in which the center axis falls in the horizontal direction, and vertical and horizontal fall of the center axis. It is required for each of the corner falls that fall in a direction that is inclined with respect to the direction. Therefore, when the cask is conveyed, as shown in Patent Documents 1 to 3, a cask cushioning body is attached to the outer surfaces of the upper and lower end portions of the cask, so that the shock applied to the cask should it be dropped. Measures to reduce are taken.

JP, 2009-186427, A JP2012-141243A JP, 2014-145674, A

By the way, inside the cask, a plurality of spent fuels are partitioned by a lattice-shaped partition plate called a basket so as not to contact each other. Since the basket thermally expands in the longitudinal direction by the heat from the spent fuel, a gap (hereinafter, referred to as a “gap”) is provided in advance between the lid portion of the cask and the basket. By providing the gap, it is possible to improve workability when attaching the lid portion of the cask to the main body portion (that is, when assembling the cask structure).

On the other hand, the provision of the gap causes a delayed drop impact when the cask falls. Delayed drop impact is when the contained objects (eg, basket and spent fuel) that are falling in the cask at the moment of collision with the ground collide with the inner surface of the cask after the collision of the cask. It is a shock that occurs in. The delayed drop impact increases as the gap described above increases.

In Patent Document 1 and Patent Document 2 described above, no consideration is given to the delayed drop impact. In Patent Document 3, in order to reduce the delayed drop impact when the cask falls vertically, an auxiliary impact absorber is attached to the outer surface of the lid of the cask in addition to the main impact absorber attached to the outer surface of the upper end of the cask. Is proposed. However, since the size of the delayed drop impact changes depending on the size of the gap as described above, in the shock absorber of Patent Document 3, the design of the auxiliary shock absorber is changed every time the size of the gap is changed. There is a need to. In addition, since it is necessary to attach a plurality of types of shock absorbers to the outer surface of the cask, the structure of the shock absorber becomes complicated, the manufacturing cost increases, and the time required to prepare the cask for transportation also increases.

The present invention has been made in view of the above problems, and an object of the present invention is to reduce the impact applied to a cask structure and an object to be accommodated when the cask falls by a simple structure.

The invention according to claim 1 is a method of manufacturing a cask capable of accommodating a fuel assembly, wherein the cask closes a tubular cask trunk and openings on both sides in the longitudinal direction of the cask trunk. A cask structure including two cask ends, an object to be housed in the internal space of the cask structure, and at least one cask end of the two cask ends. A deformable internal cushioning portion disposed between the at least one cask end portion and the at least one cask end portion including a basket capable of accommodating a fuel assembly in the longitudinally extending accommodating portion. A cask lid part detachably attached to the cask body part, wherein the cask manufacturing method is a) the longitudinal distance between the longitudinal end face of the basket and the cask lid part end face. A step of preparing the internal cushioning portion having a greater thickness in the longitudinal direction than the above, and b) attaching the cask lid portion to the cask body with the internal cushioning portion in contact with the end surface of the basket. And pressing the inner cushioning portion against the end surface of the basket to plastically deform the inner cushioning portion so that a part of the inner cushioning portion projects from the end surface of the basket into the accommodation portion.

A second aspect of the present invention is the method for manufacturing a cask according to the first aspect, wherein the internal cushioning portion covers the entire cross section of the internal space of the cask structure perpendicular to the longitudinal direction. It is provided.

A third aspect of the present invention is the method for manufacturing a cask according to the first or second aspect, wherein the internal cushioning portion is fixed to the cask lid portion in advance before the step b).

The invention according to claim 4 is the method for manufacturing a cask according to any one of claims 1 to 3, wherein the internal buffer portion is made of a porous metal.

The invention according to claim 5 is the cask manufacturing method according to any one of claims 1 to 4, wherein in the step b), the part of the internal cushioning part is provided inside the accommodating part. It contacts the longitudinal end of the fuel assembly.

According to the present invention, it is possible to reduce the impact applied to the cask structure and the contained object when the cask falls.

It is a longitudinal cross-sectional view of the cask according to the first embodiment. It is a longitudinal cross-sectional view of the upper end portion of the cask according to the second embodiment. It is a perspective view of a buffer element. It is a longitudinal cross-sectional view of the upper end portion of the cask according to the related art.

FIG. 1 is a vertical sectional view showing a cask 1 according to a first embodiment of the present invention. The cask 1 is a container capable of accommodating a spent fuel assembly 9 (hereinafter, simply referred to as "fuel assembly 9"). The cask 1 has, for example, a substantially cylindrical shape centered on a central axis J1 that faces the vertical direction in FIG. In the following description, the vertical direction in FIG. 1 is also referred to as “longitudinal direction”. FIG. 1 shows a cross section including the central axis J1 of the cask 1 (the same applies to FIGS. 2 and 4 described later).

The cask 1 has a shielding function that shields radiation, a sealing function that seals radioactive materials, a subcriticality maintaining function that maintains the fuel assembly 9 in a subcritical state, and a heat removal function that dissipates the heat of the fuel assembly 9. And so on. When the cask 1 is transported or the like, a cushioning structure (not shown) is installed on both ends in the longitudinal direction of the cask 1.

The cask 1 includes a cask structure 12 and an internal buffer section 13. The cask structure 12 includes a cask body portion 21 and two cask end portions 22 and 23. The cask body 21 has a substantially cylindrical shape centered on the central axis J1. In the example shown in FIG. 1, the cask body 21 has a substantially cylindrical shape centered on the central axis J1.

The two cask end portions 22 and 23 close the openings on both sides in the longitudinal direction of the cask body portion 21. The two cask end portions 22 and 23 are cask lid portions detachably attached to the cask body portion 21. In the following description, the cask end portion 22 that closes the upper opening of the cask body portion 21 is also referred to as “upper lid portion 22”. The cask end 23 that closes the lower opening of the cask body 21 is also referred to as a "bottom lid 23". Each of the upper lid portion 22 and the bottom lid portion 23 has a substantially columnar shape or a substantially disc shape centered on the central axis J1. The upper lid portion 22 and the bottom lid portion 23 are fixed to the cask body portion 21 by bolting, for example.

In the example shown in FIG. 1, the upper lid portion 22 includes a primary lid 221, a secondary lid 222, and a tertiary lid 223. The primary lid 221, the secondary lid 222, and the tertiary lid 223 are stacked in this order from the lower side to the upper side in FIG. Similarly to the upper lid portion 22, the bottom lid portion 23 also includes a primary lid 231, a secondary lid 232, and a tertiary lid 233. The primary lid 231, the secondary lid 232, and the tertiary lid 233 are stacked in this order from the upper side to the lower side in FIG.

The internal space 10 of the cask structure 12, that is, the space inside the cask body 21 is substantially cylindrical with the central axis J1 as the center. In other words, the cross section perpendicular to the longitudinal direction of the internal space 10 is substantially circular with the central axis J1 as the center. The internal space 10 of the cask structure 12 accommodates a plurality of fuel assemblies 9 used in the nuclear reactor. Each fuel assembly 9 has a substantially columnar shape extending in the vertical direction (that is, the longitudinal direction) in FIG. 1. The fuel assembly 9 has, for example, a substantially rectangular column shape.

The internal space 10 of the cask structure 12 is partitioned by the basket 7 extending in the longitudinal direction so that the plurality of fuel assemblies 9 do not contact each other. The shape of the basket 7 in plan view (that is, the shape viewed from the upper side or the lower side in FIG. 1) is substantially a lattice shape. In other words, the basket 7 can accommodate the fuel assembly 9 in each of the plurality of accommodating portions 71 arranged in a lattice shape and extending in the longitudinal direction. Each accommodation portion 71 is, for example, a substantially quadrangular prism-shaped space whose both ends in the longitudinal direction are open. The length of the accommodating portion 71 in the longitudinal direction is longer than the length of the fuel assembly 9 in the longitudinal direction.

The basket 7 and the plurality of fuel assemblies 9 are objects to be housed in the internal space 10 of the cask structure 12. The basket 7 and the plurality of fuel assemblies 9 are not fixed to the inner surface of the cask structure 12.

In the internal space 10 of the cask structure 12, the internal cushioning part 13 includes an object to be housed in the internal space 10 and two cask end parts 22 and 23 (that is, the top cover part 22 and the bottom cover part 23). It is located between at least one end of the cask. In the example shown in FIG. 1, the internal cushioning section 13 is arranged between the contained object and the upper lid portion 22, and between the contained object and the bottom lid portion 23. In other words, the two internal buffer portions 13 are arranged on the upper side and the lower side of the basket 7.

The structures of the two internal buffer portions 13 are substantially similar to each other. Each of the internal buffer portions 13 has a substantially disc shape or a substantially column shape centered on the central axis J1. Each internal buffer portion 13 is provided over substantially the entire cross section of the internal space 10 of the cask structure 12 which is perpendicular to the longitudinal direction. The internal cushioning portion 13 is a deformable member. The internal buffer 13 is made of, for example, a porous metal. In other words, the internal buffer portion 13 is a metal member having a void inside. The internal cushioning portion 13 may be made of, for example, foam metal or a metal member having a honeycomb structure. In the example shown in FIG. 1, the internal cushioning portion 13 is made of foam aluminum and is plastically deformable. Since the internal space 10 has a relatively high temperature when the fuel assembly 9 is accommodated in the cask structure 12, the internal buffering portion 13 is preferably made of a material having relatively high heat resistance.

The internal cushioning portion 13 located on the upper side of the basket 7 longitudinally opposes the upper end surface that is the upper end surface in the longitudinal direction of the basket 7 and the openings of the upper end portions in the longitudinal direction of the plurality of accommodating portions 71. In the example shown in FIG. 1, the internal cushioning portion 13 contacts the upper end surface of the basket 7. The internal cushioning portion 13 located on the lower side of the basket 7 is opposed to the lower end surface, which is the lower end surface in the longitudinal direction of the basket 7, and the openings of the lower end portions in the longitudinal direction of the plurality of accommodating portions 71 in the longitudinal direction. .. In the example shown in FIG. 1, the internal cushioning portion 13 contacts the lower end surface of the basket 7 in the longitudinal direction.

The internal cushioning portion 13 located on the upper side of the basket 7 is previously fixed to the lower surface of the upper lid portion 22. Then, when the upper lid portion 22 is attached to the cask body portion 21, the internal cushioning portion 13 is arranged inside the cask body portion 21 (that is, the internal space 10 ). The internal cushioning portion 13 located below the basket 7 is fixed in advance to the upper surface of the bottom lid portion 23. Then, when the bottom lid portion 23 is attached to the cask barrel portion 21, the internal cushioning portion 13 is arranged inside the cask barrel portion 21 (that is, the internal space 10 ).

In a state before the upper lid portion 22 and the bottom lid portion 23 are attached to the cask body portion 21, the thickness of the internal cushioning portion 13 fixed to the upper lid portion 22 in the longitudinal direction (that is, the thickness in the vertical direction in FIG. 1). ) Is larger than the distance in the longitudinal direction between the upper end surface of the basket 7 and the lower surface of the upper lid portion 22 shown in FIG. 1. The longitudinal thickness of the internal cushioning portion 13 fixed to the bottom lid portion 23 is greater than the longitudinal distance between the lower end surface of the basket 7 and the upper surface of the bottom lid portion 23 shown in FIG.

The upper lid portion 22 and the bottom lid portion 23 are attached to the cask body portion 21 by bolting, for example, as described above. When the bolts are tightened and the upper lid portion 22 and the bottom lid portion 23 are fixed to the cask barrel portion 21, the upper inner cushioning portion 13 is pressed against the upper end surface of the basket 7 and plastically deforms. It projects into the accommodation portion 71. Further, the inner cushioning portion 13 on the lower side is pressed against the lower end surface of the basket 7 to be plastically deformed, and protrudes from the lower end surface of the basket 7 into the plurality of accommodating portions 71. In other words, each internal cushioning portion 13 includes a plurality of protruding portions 131 that respectively protrude from the end surface of the basket 7 into the inside of the plurality of housing portions 71. The protrusion 131 preferably contacts the end of the fuel assembly 9 in the longitudinal direction inside the housing 71.

As described above, the cask 1 includes the cask structure 12 and the deformable internal cushioning portion 13. The cask structure 12 includes a cylindrical cask body portion 21 and two cask end portions 22 and 23 (that is, an upper lid portion 22 and a bottom lid portion 23). The upper lid portion 22 and the bottom lid portion 23 close the openings on both sides in the longitudinal direction of the cask body portion 21. The internal cushioning portion 13 is arranged in the internal space 10 of the cask structure 12 between an object to be accommodated in the internal space 10 and the upper lid portion 22, and between the object to be accommodated and the bottom lid portion 23. To be done.

As described above, in the cask 1, since the internal cushioning portion 13 is disposed between the contained object and the upper lid portion 22, the gap above the contained object (that is, the upper end of the contained object and the contained object). This is the distance in the longitudinal direction from the structure located on the upper side, and will be referred to as a “gap” hereinafter. Therefore, even if the cask 1 is dropped, the delayed drop impact caused by the contained object colliding with the inner surface of the cask 1 later than the collision between the cask 1 and the ground or the like can be made into a simple structure. Can be relaxed. If the cask 1 is dropped, the contained object collides with the internal buffer section 13 without directly colliding with the upper lid section 22. The internal shock-absorbing portion 13 is capable of softening the impact applied to the upper lid portion 22 by plastically deforming due to the collision with the contained object.

Further, in the cask 1, since the internal cushioning portion 13 is arranged between the contained object and the bottom lid portion 23, the gap below the contained object is also reduced. Therefore, even if the cask 1 is dropped, the above-mentioned delayed drop impact can be mitigated with a simple structure. If the cask 1 is dropped, the contained object collides with the internal cushioning portion 13 without directly colliding with the bottom lid portion 23. The internal shock-absorbing part 13 can soften the impact applied to the bottom cover part 23 by being plastically deformed by the collision with the contained object.

As described above, even if the cask 1 is dropped, the shock absorbing function of the upper lid portion 22 and the bottom lid portion 23 is mitigated by the internal cushioning portion 13, so that the shielding function and the sealing function of the cask 1 are impaired. This can be prevented or suppressed. Further, it is possible to prevent or suppress the damage of the housed object (that is, at least one of the basket 7 and the fuel assembly 9) due to the collision with the inner surface of the cask 1.

In the cask 1, when the temperature of the contained object (for example, the basket 7) rises and the thermal expansion occurs in the longitudinal direction, the internal buffer portion 13 is pressed by the contained object toward the upper lid portion 22 or the bottom lid portion 23. Plastically deforms. Therefore, it is possible to prevent the contained object from being damaged due to the inhibition of thermal expansion.

In the cask 1, the internal cushioning part 13 may be arranged between the object to be housed in the internal space 10 and at least one of the top cover part 22 and the bottom cover part 23. In other words, the internal cushioning portion 13 is arranged between at least one of the two cask end portions 22 and 23 and the contained object. Thereby, even if the cask 1 is dropped, the delayed drop impact described above can be mitigated with a simple structure. As a result, it is possible to prevent or suppress the loss of the shielding function and the sealing function of the cask 1. Further, it is possible to prevent or suppress the damage of the housed object (that is, at least one of the basket 7 and the fuel assembly 9) due to the collision with the inner surface of the cask 1.

In the cask 1, at least one of the cask end portions described above is a cask lid portion that is detachably attached to the cask body portion 21. Further, the internal cushioning portion 13 is fixed to the cask lid portion. Therefore, by attaching the cask lid portion to the cask body portion 21, the internal cushioning portion 13 can be easily arranged at a predetermined position in the internal space 10 of the cask structure 12. In the example shown in FIG. 1, both the upper and lower internal cushioning parts 13 of the contained object can be easily arranged at respective predetermined positions in the internal space 10.

As described above, the contained object of the cask 1 includes the basket 7 capable of accommodating the fuel assembly 9 in the accommodating portion 71 extending in the longitudinal direction. The internal cushioning portion 13 faces the end face of the basket 7 in the longitudinal direction and the opening of the end portion of the accommodating portion 71 in the longitudinal direction in the longitudinal direction. As a result, the impact of delayed fall due to the basket 7 and the fuel assembly 9 can be mitigated. As a result, it is possible to further suppress or prevent the shielding function and the sealing function of the cask 1 from being impaired. Further, damage to the basket 7 and the fuel assembly 9 due to collision with the inner surface of the cask 1 can be prevented or suppressed.

The inner cushioning portion 13 preferably contacts the end face in the longitudinal direction of the basket 7. As a result, it is possible to further mitigate the delayed drop impact of the basket 7. Further, the damage of the basket 7 due to the collision with the inner surface of the cask 1 can be further prevented or suppressed.

The internal cushioning portion 13 preferably includes a protrusion 131 that protrudes from the end surface of the basket 7 into the inside of the accommodation portion 71. As a result, the delayed drop impact caused by the fuel assembly 9 can be further alleviated. Further, the damage of the fuel assembly 9 due to the collision with the inner surface of the cask 1 can be further suppressed or prevented.

The protrusion 131 preferably contacts the end of the fuel assembly 9 in the longitudinal direction inside the housing 71. As a result, the delayed drop impact caused by the fuel assembly 9 can be further alleviated. Further, it is possible to further suppress or prevent the damage of the fuel assembly 9 due to the collision with the inner surface of the cask 1.

As described above, the internal cushioning portion 13 is provided over the entire surface of the cross section of the internal space 10 of the cask structure 12 which is perpendicular to the longitudinal direction. This makes it possible to further mitigate the delayed drop impact caused by the basket 7 and the fuel assembly 9. Further, damage to the basket 7 and the fuel assembly 9 due to the collision with the inner surface of the cask 1 can be further suppressed or prevented. The internal buffering portion 13 does not need to be provided strictly over the entire surface in the above-mentioned cross section of the internal space 10, and may be provided over substantially the entire surface. As a result, similarly to the above, the delayed drop impact caused by the basket 7 and the fuel assembly 9 can be further mitigated, and the damage to the basket 7 and the fuel assembly 9 can be further suppressed or prevented.

In the cask 1, the internal buffer 13 is made of porous metal. This makes it easy to manufacture the internal buffer 13 and install it in the internal space 10. Further, even when the above-mentioned gap is changed due to a change in the length of the housed object in the longitudinal direction or the like, for example, it is easily dealt with by simply changing the thickness of the internal cushioning portion 13 in the longitudinal direction. be able to. As described above, the internal buffer portion 13 is made of foam metal. Therefore, it is possible to further easily manufacture the internal cushioning portion 13 and install it in the internal space 10. In the example shown in FIG. 1, the internal buffer portion 13 is made of foam aluminum. As a result, the drop shock absorbing performance of the internal cushioning portion 13 can be made substantially equal to the drop shock absorbing performance of the above-mentioned cushioning structure made of wood that is exteriorly mounted on the longitudinal end portion of the cask 1.

FIG. 2 is a vertical cross-sectional view showing the upper end portion of the cask 1a according to the second embodiment. In the cask 1a, instead of the internal buffer section 13 shown in FIG. 1, an internal buffer section 13a having a different structure is arranged in the internal space 10. The other configuration of the cask 1a is substantially the same as that of the cask 1 shown in FIG. 1, and in the following description, the corresponding components are designated by the same reference numerals.

The internal cushioning portion 13a includes a plurality of cushioning elements 132. FIG. 3 is an enlarged perspective view of one cushioning element 132. The other cushioning element 132 has substantially the same structure as the cushioning element 132 shown in FIG. Each cushioning element 132 is, for example, tubular (that is, tubular). Each cushioning element 132 is a plastically deformable member made of metal. In the example shown in FIG. 3, the cushioning element 132 has a substantially cylindrical shape extending in the longitudinal direction. The shape of the cushioning element 132 may be variously changed. The cushioning element 132 may have, for example, a substantially cylindrical shape (that is, a substantially frustoconical shape) whose diameter gradually increases or decreases from one side in the longitudinal direction toward the other side.

In the cask 1a shown in FIG. 2, as in the cask 1 shown in FIG. 1, the internal cushioning portion 13a includes an object to be accommodated in the internal space 10, an upper lid portion 22 and a bottom lid portion 23 (see FIG. 1). It is arranged between at least one of them. In other words, the internal cushioning portion 13a is arranged between at least one of the two cask end portions 22 and 23 and the contained object. As a result, the gap on at least one of the upper side and the lower side of the housed object becomes small, so that the delayed drop impact due to the housed object can be mitigated with a simple structure. As a result, it is possible to prevent or suppress the loss of the shielding function and the sealing function of the cask 1a.

If the cask 1a is dropped, the contained object collides with the plurality of cushioning elements 132 of the internal cushioning portion 13a. The plurality of cushioning elements 132 are crushed in the longitudinal direction (that is, plastically deformed) due to the collision with the contained object. Thereby, the impact applied to the upper lid portion 22 or the bottom lid portion 23 can be mitigated. As a result, it is possible to prevent or suppress damage to the contained object (that is, at least one of the basket 7 and the fuel assembly 9) due to the collision with the inner surface of the cask 1a.

In the cask 1a, when the temperature of the object to be contained (for example, the basket 7) rises and the thermal expansion occurs in the longitudinal direction, the internal buffer portion 13a is pressed toward the upper lid part 22 or the bottom lid part 23 by the object to be contained. Plastically deforms. Therefore, it is possible to prevent the contained object from being damaged due to the inhibition of thermal expansion.

In the cask 1a, the plurality of cushioning elements 132 of the inner cushioning portion 13a are fixed to the upper lid portion 22 or the bottom lid portion 23. Therefore, by attaching the upper lid portion 22 or the bottom lid portion 23 to the cask body portion 21, the internal cushioning portion 13a can be easily arranged at a predetermined position in the internal space 10 of the cask structure 12.

The plurality of cushioning elements 132 of the inner cushioning portion 13a longitudinally oppose the end face in the longitudinal direction of the basket 7 and the opening at the longitudinal end of the accommodating portion 71. As a result, the impact of delayed fall due to the basket 7 and the fuel assembly 9 can be mitigated. Further, damage to the basket 7 and the fuel assembly 9 due to collision with the inner surface of the cask 1a can be prevented or suppressed.

A part of the cushioning element 132 of the inner cushioning portion 13 a preferably contacts the longitudinal end surface of the basket 7. As a result, it is possible to further mitigate the delayed drop impact caused by the basket 7. Further, the damage of the basket 7 due to the collision with the inner surface of the cask 1a can be further prevented or suppressed.

A part of the cushioning element 132 of the inner cushioning portion 13 a projects from the end surface of the basket 7 into the accommodation portion 71. In other words, the internal cushioning portion 13a includes a protruding portion that protrudes from the end surface of the basket 7 into the accommodation portion 71. As a result, the delayed drop impact caused by the fuel assembly 9 can be further alleviated. Further, the damage of the fuel assembly 9 due to the collision with the inner surface of the cask 1a can be further suppressed or prevented. The cushioning element 132 projecting inside the accommodating portion 71 preferably contacts the longitudinal end portion of the fuel assembly 9. As a result, the delayed drop impact caused by the fuel assembly 9 can be further alleviated. Further, it is possible to further suppress or prevent the damage of the fuel assembly 9 due to the collision with the inner surface of the cask 1a.

The plurality of cushioning elements 132 of the inner cushioning portion 13a are provided over substantially the entire cross section of the internal space 10 of the cask structure 12 perpendicular to the longitudinal direction. This makes it possible to further mitigate the delayed drop impact caused by the basket 7 and the fuel assembly 9. Further, damage to the basket 7 and the fuel assembly 9 due to the collision with the inner surface of the cask 1a can be further suppressed or prevented.

FIG. 4 is a vertical cross-sectional view showing the upper end portion of the cask 1b according to the related art of the present invention. In the cask 1b, instead of the internal cushioning portion 13 shown in FIG. 1, an internal cushioning portion 13b having a different structure is arranged in the internal space 10. The other configuration of the cask 1b is substantially the same as that of the cask 1 shown in FIG. 1, and in the following description, the corresponding components are designated by the same reference numerals.

The internal cushioning portion 13b includes a facing member 133 and an elastic member 134. The facing member 133 is a substantially disk-shaped or substantially columnar member centered on the central axis J1. The facing member 133 faces the object in the internal space 10 of the cask structure 12 in the longitudinal direction. The elastic member 134 is arranged between the facing member 133 and the upper lid portion 22 or the bottom lid portion 23 (see FIG. 1). The elastic member 134 includes a plurality of elastic elements 135 fixed to the facing member 133. In the example shown in FIG. 4, each elastic element 135 is, for example, a coil spring made of metal, and the lower end portion is fixed to the upper surface of the facing member 133. The upper end portion of each elastic element 135 is fixed to the lower surface of the upper lid portion 22. The elastic element 135 is elastically deformable in the longitudinal direction. The elastic element 135 is in a longitudinally compressed state. The elastic element 135 is not limited to a coil spring and may be, for example, a leaf spring.

In the cask 1b, as in the cask 1 shown in FIG. 1, the internal cushioning portion 13b is provided for the contained object accommodated in the internal space 10 and at least one of the top lid portion 22 and the bottom lid portion 23 (see FIG. 1). It is placed between the parts. In other words, the internal cushioning portion 13b is arranged between at least one of the two cask end portions 22 and 23 and the contained object. As a result, the gap on at least one of the upper side and the lower side of the housed object becomes small, so that the delayed drop impact caused by the housed object can be mitigated. As a result, it is possible to prevent or suppress the loss of the shielding function and the sealing function of the cask 1b with a simple structure.

If the cask 1b is dropped, the contained object collides with the facing member 133 of the internal cushioning portion 13b, and the plurality of elastic elements 135 of the elastic member 134 elastically deforms in the longitudinal direction. Thereby, the impact applied to the upper lid portion 22 or the bottom lid portion 23 can be mitigated. As a result, it is possible to prevent or suppress damage to the contained object (that is, at least one of the basket 7 and the fuel assembly 9) due to the collision with the inner surface of the cask 1b.

In the cask 1b, as described above, the internal cushioning portion 13b is disposed between the facing member 133 having an end face facing the object in the longitudinal direction and between the facing member 133 and the at least one cask end. The elastic member 134 is elastically deformable in the longitudinal direction. Therefore, when the temperature of the housed object (for example, the basket 7) rises and thermally expands in the longitudinal direction, the internal cushioning portion 13b is pressed by the housed object toward the upper lid portion 22 or the bottom lid portion 23, and elastic The member 134 elastically deforms and the facing member 133 moves in the longitudinal direction toward the upper lid portion 22 or the bottom lid portion 23. As a result, it is possible to prevent the contained object from being damaged due to the inhibition of thermal expansion. Further, when the temperature of the contained object decreases and contracts in the longitudinal direction, the restoring force of the elastic member 134 causes the opposing member 133 to move in the longitudinal direction in a direction away from the upper lid portion 22 or the bottom lid portion 23. Therefore, the gap on the upper side or the lower side of the contained object can be maintained in a small state. As a result, it is possible to mitigate the delayed drop impact of the contained object. In other words, the internal buffer portion 13b can easily cope with thermal deformation of the contained object.

In the cask 1b, the plurality of elastic elements 135 of the internal cushioning portion 13b are fixed to the upper lid portion 22 or the bottom lid portion 23, and the facing member 133 is fixed to the plurality of elastic elements 135. Therefore, by attaching the upper lid portion 22 or the bottom lid portion 23 to the cask body portion 21, the internal cushioning portion 13b can be easily arranged at a predetermined position in the internal space 10 of the cask structure 12.

The facing member 133 of the internal cushioning portion 13b longitudinally faces the end face of the basket 7 in the longitudinal direction and the opening of the end portion of the accommodating portion 71 in the longitudinal direction. As a result, the impact of delayed fall due to the basket 7 and the fuel assembly 9 can be mitigated. Further, damage to the basket 7 and the fuel assembly 9 due to the collision with the inner surface of the cask 1b can be prevented or suppressed.

The facing member 133 of the internal cushioning portion 13b preferably contacts the end face of the basket 7 in the longitudinal direction. As a result, it is possible to further mitigate the delayed drop impact caused by the basket 7. Further, the damage of the basket 7 due to the collision with the inner surface of the cask 1b can be further prevented or suppressed. In the internal cushioning portion 13b, the elastic member 134 elastically deforms, so that the contact state between the facing member 133 and the end surface of the basket 7 can be maintained regardless of the temperature change of the basket 7.

The facing member 133 may include a protrusion that protrudes from the end surface of the basket 7 into the accommodation portion 71. As a result, the delayed drop impact caused by the fuel assembly 9 can be further alleviated. Further, the damage of the fuel assembly 9 due to the collision with the inner surface of the cask 1b can be further suppressed or prevented. The protrusion preferably contacts the longitudinal end of the fuel assembly 9. As a result, the delayed drop impact caused by the fuel assembly 9 can be further mitigated. Further, it is possible to further suppress or prevent the damage of the fuel assembly 9 due to the collision with the inner surface of the cask 1b.

The facing member 133 of the internal cushioning portion 13b is provided over substantially the entire cross section of the internal space 10 of the cask structure 12 which is perpendicular to the longitudinal direction. This makes it possible to further mitigate the delayed drop impact caused by the basket 7 and the fuel assembly 9. Further, the damage of the basket 7 and the fuel assembly 9 due to the collision with the inner surface of the cask 1b can be further suppressed or prevented.

Various changes can be made to the casks 1, 1a, 1b described above.

For example, the internal cushioning portions 13, 13a, 13b are not necessarily fixed to the upper lid portion 22 or the bottom lid portion 23, and may be members independent of the upper lid portion 22 and the bottom lid portion 23. Further, the internal buffer portions 13, 13a, 13b may be provided only on a part of the cross section of the internal space 10 perpendicular to the longitudinal direction.

In the internal cushioning portions 13, 13a, 13b, the protrusions that project from the end surface of the basket 7 into the accommodation portion 71 are, for example, the internal cushioning portions 13, 13a arranged between the upper lid portion 22 and the object to be accommodated. , 13b may be provided only. In the related art of the present invention, the protrusions do not necessarily have to be provided in the internal buffer portions 13, 13a, 13b. Further, the internal cushioning portions 13, 13 a, 13 b may not be in contact with the end surface of the basket 7. Further, the internal buffer portions 13, 13a, 13b may face only the end surface of the basket 7 in the longitudinal direction, or may face only the housing portion 71 of the basket 7 in the longitudinal direction.

In the related art of the present invention, the above-mentioned contained object does not necessarily need to include the fuel assembly 9 and the basket 7, and various objects may be included.

The internal buffer portions 13, 13a, 13b may be arranged only between the contained object and the upper lid portion 22, or may be arranged only between the contained object and the bottom lid portion 23. The structure of the internal buffer section is not limited to the structure of the internal buffer sections 13, 13a, 13b described above, and may be variously modified.

The structure of the cask structure 12 may also be variously modified. For example, instead of the bottom lid portion 23 attached to the cask body portion 21, a cask end portion that is a member connected to the cask body portion 21 may be provided.

The configurations of the above-described embodiment and each modification may be appropriately combined unless they contradict each other.

1, 1a, 1b Cask 7 Basket 9 Fuel assembly 10 Internal space 12 Cask structure 13, 13a, 13b Internal buffer 21 Cask body 22 Upper lid 23 Bottom lid 31 Protrusion 71 Receiving portion 133 Opposing member 134 Elastic member

Claims (5)

A method of manufacturing a cask capable of accommodating a fuel assembly, comprising:
The cask is
A cask structure including a tubular cask body, and two cask end portions that close openings on both sides in the longitudinal direction of the cask body,
In the internal space of the cask structure, a deformable internal cushioning section arranged between an object to be housed in the internal space and at least one cask end of the two cask ends.
Equipped with
The contained object includes a basket capable of accommodating a fuel assembly in the accommodating portion extending in the longitudinal direction,
The at least one cask end portion is a cask lid portion detachably attached to the cask body portion,
The manufacturing method of the cask,
a) preparing the internal cushioning portion having a thickness in the longitudinal direction larger than a distance in the longitudinal direction between the longitudinal end surface of the basket and an end surface of the cask lid portion;
b) by attaching the cask lid portion to the cask body while the internal cushioning portion is in contact with the end surface of the basket, the internal cushioning portion is pressed against the end surface of the basket to be plastically deformed, and Projecting a part of the internal cushioning part from the end face of the basket into the inside of the housing part;
A method of manufacturing a cask, comprising: A method of manufacturing a cask according to claim 1, wherein
The method for manufacturing a cask, wherein the internal buffer portion is provided over the entire surface of a cross section of the internal space of the cask structure perpendicular to the longitudinal direction. A method of manufacturing a cask according to claim 1 or 2, wherein
The method for manufacturing a cask, wherein the internal cushioning part is fixed to the cask lid part in advance before the step b). A method of manufacturing a cask according to any one of claims 1 to 3,
The method for manufacturing a cask, wherein the internal buffer portion is made of a porous metal. A method of manufacturing a cask according to any one of claims 1 to 4,
In the step b), the cask manufacturing method is characterized in that the part of the internal buffer portion contacts the end portion in the longitudinal direction of the fuel assembly inside the accommodation portion.

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