Buffers and radioactive material storage containers

Abstract

To provide a buffer and a radioactive material storage container that can exhibit appropriate cushioning performance against collisions in an inclined state. [Solution] The buffer is installed on the axial end face of a radioactive material storage container having a cask body and a lid that is supported by the flange portion of the cask body and seals the cask body. In an axial view, the ratio of the area of ​​the installation area to the area of ​​the flange portion is 0.8 or more, and the buffer absorbs impact by deforming.

Description

Technical Field

[0001] The present disclosure relates to a shock absorber and a radioactive substance storage container.

Background Art

[0002] In nuclear facilities, radioactive waste such as spent fuel generated in nuclear reactors and the like is stored in a radioactive substance storage container (cask), transported to a storage facility, reprocessing facility or the like, and stored or reprocessed. The radioactive substance storage container is composed of a cylindrical body portion with a bottom and an open top, and a lid portion fixed to the top of the body portion to close the opening.

[0003] After transportation, the radioactive substance storage container is stored in a storage location for several decades. The radioactive substance storage container during storage is provided with a shock absorber made of steel material at least on the peripheral surface side of the axial end portion, and deforms when colliding with a floor, wall or the like due to dropping, overturning or moving, thereby absorbing the impact applied in the radial direction (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, it is difficult for the shock absorber arranged in the radial direction to secure an effective shock absorber volume when assuming a collision of the radioactive substance storage container in an inclined state. On the other hand, when installing a shock absorber on the axial end face side, a structure that receives the reaction force when the shock absorber is crushed is required, which must not interfere during a radial collision. In addition, since the axial end face of the cask main body has a sealing boundary portion between the lid portion and the body portion, it is necessary to prevent excessive load from entering and impairing the sealing integrity.

[0006] This disclosure aims to solve the aforementioned problems and to provide a buffer and a radioactive material storage container that can exhibit appropriate buffering performance against collisions in an inclined state. [Means for solving the problem]

[0007] To achieve the above-mentioned objectives, a buffer according to one aspect of the present disclosure is installed on the axial end face of a radioactive material storage container having a cask body and a lid supported by the flange portion of the cask body and sealing the cask body, characterized in that, in an axial view, the ratio of the area of ​​the installation area to the area of ​​the coincidence area where the installation area and the flange portion coincide is 0.8 or more, and it absorbs impact by deforming.

[0008] Furthermore, a buffer according to another aspect of the present disclosure includes a radial buffer for a radioactive material storage container having a cask body and a lid portion that seals the cask body, the radial buffer protruding radially outward from the cask body and supported on the outer circumferential surface of the cask body, and absorbing radial impact by deforming; and an axial buffer protruding axially outward from the axial end face of the radioactive material storage container and supported on the end face, and absorbing axial impact by deforming, wherein the radial buffer and the axial buffer are arranged so as not to come into contact with each other.

[0009] To achieve the above-mentioned objective, a radioactive material storage container according to one aspect of the present disclosure is characterized by comprising a cask body, a lid that seals the cask body, and the buffer. [Effects of the Invention]

[0010] According to this disclosure, the effect of being able to exhibit appropriate cushioning performance against collisions in an inclined state can be obtained. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a perspective view showing a section of a radioactive material containment container that has been fractured. [Figure 2] Figure 2 is a cross-sectional view showing the main part of a radioactive material containment container fitted with a buffer. [Figure 3] Figure 3 is an axial view showing a radioactive material containment container fitted with a buffer. [Figure 4] Figure 4 is a front view showing a radioactive material storage container with a buffer installed in a horizontal position. [Figure 5] Figure 5 is a schematic plan view illustrating an example of an inclined collision involving a radioactive material containment container equipped with a buffer. [Figure 6] Figure 6 is a schematic diagram illustrating the installation range of the axial buffer. [Figure 7] Figure 7 is an axial view showing a first modified example of the installation range of the axial buffer. [Figure 8] Figure 8 is an axial view showing a second modified example of the installation range of the axial buffer. [Modes for carrying out the invention]

[0012] Embodiments relating to this disclosure will be described in detail below with reference to the drawings. However, the invention is not limited by these embodiments. Furthermore, the components in the embodiments described below include those that are easily substituted, substantially identical, or equivalent to those that can be substituted by those skilled in the art. In addition, various omissions, substitutions, or modifications of components in the embodiments described below are permitted without departing from the spirit of this disclosure. In the embodiments described below, necessary components will be described to illustrate the embodiments, while other components will be omitted, and identical components will be denoted by the same reference numerals, while different components will be denoted by different reference numerals.

[0013] [Storage container for radioactive materials] First, an example of the configuration of a radioactive material storage container according to this embodiment will be described using Figure 1. Figure 1 is a perspective view of a portion of the radioactive material storage container with a section broken.

[0014] As shown in Figure 1, a cask 11 serving as a radioactive material storage container includes a cask body 12 and a lid part 13.

[0015] The cask body 12 has a main body barrel 21. The main body barrel 21 has a cylindrical shape (in the present embodiment, a circular cylindrical shape). The main body barrel 21 has an opening 22 formed at one axial end (the upper end in Figure 1) of the cylindrical shape, and the other end (the lower end in Figure 1) is closed. The main body barrel 21 has a cavity 23 inside. A basket 24 is provided in the cavity 23. The basket 24 is provided with a plurality of cells 25 capable of independently storing radioactive materials (for example, spent fuel assemblies). The main body barrel 21 is a carbon steel forged product having a gamma ray shielding function, but stainless steel may be used instead of carbon steel, and it may also be a cast product such as spheroidal graphite cast iron or carbon steel cast steel.

[0016] The cask body 12 further includes an outer cylinder 26, heat transfer fins 27, and a resin (neutron shield) 28. The outer cylinder 26 is disposed on the outer peripheral surface of the main body barrel 21 with a predetermined gap therebetween. A plurality of the heat transfer fins 27 are provided in the circumferential direction between the outer peripheral surface of the main body barrel 21 and the inner peripheral surface of the outer cylinder 26. The heat transfer fins 27 are made of copper, and conduct heat between the outer peripheral surface of the main body barrel 21 and the inner peripheral surface of the outer cylinder 26. The resin 28 is provided in a space portion surrounded by the main body barrel 21, the outer cylinder 26, and the heat transfer fins 27. The resin 28 is a polymer material containing a large amount of hydrogen, and contains boron or a boron compound having a neutron shielding function.

[0017] The cask body 12 further has a bottom portion 29. The bottom portion 29 is provided so as to protrude axially outward (below the lower end in Figure 1) at the other closed end of the main body barrel 21. The bottom portion 29 has a space portion surrounded by the other closed end of the main body barrel 21, and a resin (neutron shield) is provided in the space portion.

[0018] The cask body 12 is provided with trunnions 30 for lifting the cask 11 on the main body barrel 21. The trunnions 30 are provided to penetrate from the main body barrel 21 through the outer cylinder 26, and protrude to the outermost periphery of the cask 11.

[0019] The lid part 13 is provided at the opening 22 of the main body cylinder 21, and closes the opening 22 to hermetically seal the main body cylinder 21 (the cask main body 12). The lid part 13 is configured to include a primary lid 31, a secondary lid 32, and a tertiary lid 33. The primary lid 31 is formed in a disk shape using carbon steel or stainless steel that shields gamma rays as a material. The secondary lid 32 covers the axially outer side of the primary lid 31, and like the primary lid 31, is formed in a disk shape using carbon steel or stainless steel that shields gamma rays as a material. A resin (neutron shield) 28 may be provided between the primary lid 31 and the secondary lid 32. The tertiary lid 33 covers the secondary lid 32 and the end edge 22c of the main body cylinder 21 and appears on the outer side of the cask 11, and like the primary lid 31 and the secondary lid 32, is formed in a disk shape using carbon steel or stainless steel that shields gamma rays as a material. During storage, the lid part 13 may be provided with an adapter for attaching a buffer body 50 described later in place of the tertiary lid 33.

[0020] The primary lid 31 is fixed to the first stepped portion 22a formed in the opening 22 of the main body cylinder 21 by bolts (not shown) made of carbon steel or stainless steel, and is attached to the main body cylinder 21. The secondary lid 32 is fixed to the second stepped portion 22b formed in the opening 22 of the main body cylinder 21 by bolts (not shown) made of carbon steel or stainless steel, and is attached to the main body cylinder 21. Although not shown, metal gaskets are provided between the primary lid 31 and the first stepped portion 22a and between the secondary lid 32 and the second stepped portion 22b. The metal gaskets ensure sealing performance between the primary lid 31 and the first stepped portion 22a and between the secondary lid 32 and the second stepped portion 22b.

[0021] In the cask main body 12, a cylindrical end edge 22c surrounding the secondary lid 32 and appearing on the outer side of the cask 11 is formed at the opening 22 of the main body cylinder 21. The end edge 22c has a surface (in FIG. 1, the upper surface) located on the outer side of the main body cylinder 21 (in FIG. 1, at a higher position) than the surface of the secondary lid 32, and surrounds the secondary lid 32. On the surface of the end edge 22c, a plurality of bolt holes (not shown) for attaching the tertiary lid 33, or the adapter and the buffer body are provided at intervals in the circumferential direction.

[0022] [Buffer] Next, an example of the buffer configuration according to this embodiment will be described using Figures 2 to 4. Figure 2 is a cross-sectional view showing the main part of a radioactive material storage container fitted with a buffer. Figure 3 is an axial view showing a radioactive material storage container fitted with a buffer. Figure 4 is a front view showing a radioactive material storage container fitted with a buffer in a horizontal position.

[0023] As shown in Figures 2, 3, and 4, the cask 11 has a buffer unit 1. The buffer unit 1 comprises buffers 40 and 50. The buffers 40 and 50 are attached to the cask 11 when it is transported to a storage facility, which is a storage location.

[0024] In a nuclear power plant, for example, spent fuel assemblies are stored in the cells 25 of the basket 24 of the main body shell 21 of the cask 11, and sealed by the lid 13. The cask 11 is transported, for example, from the nuclear power plant to a storage facility. When transporting the cask 11 within the power plant premises, a buffer unit 1, which is a storage buffer, is attached to it, and when transporting it outside the power plant premises, a transport buffer (not shown) is attached to it.

[0025] The casks 11, transported to the storage facility, are stored horizontally with their central axis O aligned horizontally, as shown in Figure 4. The casks 11 are placed on a stand 38 on which the cask body 12 is installed on the floor F, and are stored horizontally with their central axis O aligned horizontally. In this case, the casks 11 have buffers 40a and 50a attached to one side (lid 13 side) along the central axis O. The casks 11 also have buffers 40b and 50b attached to the other side (bottom 29 side) along the central axis O. In the following description, if buffers 40a and 40b are not distinguished, they will be referred to as buffer 40, and if buffers 50a and 50b are not distinguished, they will be referred to as buffer 50. The stand 38 is not limited to the configuration shown in Figure 4, and it is preferable, for example, to have a base that is wider than the projected area of ​​the casks 11 in plan view. This prevents the entire mounting frame 38 from moving unintentionally during abnormal events such as earthquakes or tornadoes, thus preventing collisions between the casks 11 stored side by side.

[0026] The cask 11 may also be stored in a vertical position with its central axis O aligned vertically. In this case, the cask 11 is stored upright on the floor F with its lid 13 facing upwards, and buffers 40a and 50a are attached to the lid 13 side. Alternatively, when the cask 11 is stored, its bottom 29 may be fitted into a stand (not shown) installed on the floor F, or the trunnion 30 may be secured to the stand, and the cask 11 may be stored in a vertical position with its central axis O aligned vertically.

[0027] The buffer 40 is a radial buffer that absorbs impact by deforming in response to a predetermined load applied to the cask 11, primarily in the radial direction. The predetermined load includes, for example, the load of a falling object, the load applied to the cask 11 when it falls from a vertical position or when it hits the floor F, and the load applied when the cask 11 or surrounding equipment slides laterally during an earthquake and hits another cask 11. The buffer 40 is positioned at the axial end of the cask 11 so as to surround the outside of the edge 22c of the cask body 12. That is, the buffer 40 protrudes radially outward from the lid 13 and radially outward from the cask body 12, and is supported by the outer circumferential surface of the cask body 12.

[0028] The buffer body 40 is made of a porous metal such as aluminum, and is deformable by a predetermined load. The buffer body 40 may be formed as an annular shape made of aluminum or the like, with a structure having a plurality of holes that penetrate in the radial direction. The buffer body 40 may have, for example, a support member provided in a hollow shape, and a buffer material arranged and supported inside the support member. The support member is made of a metal plate such as a steel plate, and the buffer material is made of a porous metal such as aluminum. In addition, wood or foamed resin may be used as the buffer material for the buffer body 40.

[0029] The buffer 40 is attached, for example, to a support member 41 provided on the outer circumference of the cask body 12. The support member 41 in this embodiment is provided in an annular shape surrounding the outer circumference of the cask body 12 and has flanges that protrude radially outward from both axial ends. The buffer 40 is restricted from moving in the axial direction by being sandwiched by the flanges. The support member 41 may have only flanges and may be extended from the outer surface of the cask body 12 by welding or the like after the buffer 40 is attached to the cask body 12. Alternatively, as shown in Figure 2, the cask body 12 at the location where the buffer 40 is provided may have a smaller diameter than other parts, and this difference in diameter may be used to restrict the axial movement of the buffer 40. Note that the support member 41 will not be depicted in Figures 3 and later.

[0030] The buffer 50 is an axial buffer that absorbs impact by deforming in response to a predetermined load mainly applied axially to the cask 11. The predetermined load is, for example, the load applied to the cask 11 when it hits the floor F or wall when it detaches from the stand 38 and falls while tilting, or when the stand 38 moves.

[0031] The buffer 50a is positioned at the end of the cask 11 on the side where the axial lid 13 is provided, covering the surface of the edge 22c of the cask body 12, and substantially coinciding with the extent of the edge 22c. The buffer 50a is positioned at the end of the cask 11 on the side where the axial lid 13 is provided, along the surface of the tertiary lid 33 or adapter that appears outside the lid 13 and the surface of the edge 22c of the cask body 12. The buffer 50b is positioned at the end of the cask 11 on the side where the axial bottom 29 is provided, inside the outer circumference of the bottom 29. The buffer 50b is positioned at the end of the cask 11 on the side where the axial bottom 29 is provided, covering the surface of the bottom 29 and the surface of the edge of the cask body 12. That is, the buffers 50a and 50b protrude axially outward from the axial end face of the cask 11 and are supported by the end face.

[0032] The buffer 50 is positioned along the outer edges of the lid 13 and bottom 29 in an axial view, and is not positioned in the center. In this embodiment, the buffer 50 has an annular shape in an axial view. The buffer 50 is positioned so as not to come into contact with the buffer 40. The installation range of the buffer 50 will be described in detail later.

[0033] The buffer 50 is made of a porous metal such as aluminum, and is deformable under a predetermined load. The buffer 50 may be formed as an annular shape made of aluminum or the like, with a structure having a plurality of holes that penetrate in the axial direction. The buffer 50 may have, for example, a support member provided in a hollow shape, and a buffer material arranged and supported inside the support member. The support member is made of a metal plate such as a steel plate, and the buffer material is made of a porous metal such as aluminum. The buffer 50 may also use wood or foamed resin as the buffer material.

[0034] The buffer body 50 is fixed to the main body 21 by bolts (not shown) attached to bolt holes (not shown) provided on the surface of the main body 21. When a tertiary cover 33 is provided as the cover portion 13, the buffer body 50 is positioned along the surface of the tertiary cover 33 that is exposed on the outside of the cover portion 13, and is positioned to cover the surface of the tertiary cover 33 and the edge 22c of the main body 21. The buffer body 50 is fixed to the bottom portion 29 by bolts (not shown) attached to bolt holes (not shown) provided on the surface of the bottom portion 29.

[0035] [Tilt collision] Next, the definition of inclined collision in this specification will be explained using Figure 5. Figure 5 is a schematic plan view showing an example of an inclined collision involving a radioactive material containment container equipped with a buffer.

[0036] As shown in Figure 4, the casks 11 transported to the storage facility are fitted into a frame 38 installed on the floor F, and stored in a horizontal position with their central axis O aligned horizontally. In the storage facility, multiple casks 11 fitted into the frame 38 are lined up horizontally, the entire arrangement is covered with reinforced concrete panels, and they are joined together with bolts or the like for storage.

[0037] In this embodiment, it is assumed that during abnormal events such as earthquakes or tornadoes, the cask 11 may detach from the frame 38, or the frame 38 may move, causing the cask 11 to collide with objects S such as concrete panels, surrounding equipment, or other casks installed nearby. The purpose is to ensure safety against such collisions. As shown in Figure 5, it is assumed that the center of gravity G of the cask 11 approaches the object S perpendicularly, and the buffer 50 collides with the object S at a predetermined speed. In this case, the collision angle θ between the surface of the object S and the end face of the buffer 50 is greater than 0° and within a range where the surface of the object S and the buffer 40 do not collide. In other words, only a portion of the buffer 50 is assumed to bear the reaction force from the collision with the object S.

[0038] [Installation range and dimensions of axial buffer] Next, the installation range and dimensions of the buffer 50 will be explained using Figures 2 and 6. Figure 6 is a schematic diagram illustrating the installation range of the axial buffer.

[0039] First, the radial installation range of the buffer 50 will be described. As shown in Figure 2, in an axial view, the installation range of the buffer 50 generally coincides with the flange portion (second stage portion 22b in this embodiment) of the cask body 12 that supports the outermost lid of the lid portion 13 (secondary lid 32 in this embodiment). Generally coincides means that in an axial view, the ratio of the area Ad of the coincidence range where the buffer 50 installation range and the flange portion coincide to the area Ac of the buffer 50 installation range is 0.8 or more (Ad / Ac ≥ 0.8). Furthermore, in an axial view, it is preferable that the ratio of the area Ad of the coincidence range where the buffer 50 installation range and the flange portion coincide to the area Af of the flange portion is 0.8 or more (Ad / Af ≥ 0.8). By setting the ranges of Ad / Ac and Ad / Af to the above ranges, the buffer 50 can appropriately support the load when it deforms.

[0040] Next, the dimensions of the buffer 50 will be explained. As shown in Figure 6, in a plan view, a virtual line VL is defined connecting the corner of the cask body 12 on the side that collides with the object S to be struck and the center of gravity G of the cask 11, and a virtual plane VP is defined perpendicular to the virtual plane VL and passing through the said corner. Assuming that the portion of the buffer 50 cut by the virtual plane VP is the assumed crushed portion V during an inclined collision, the amount of compressive strain of the buffer 50 is expressed as the ratio (H2 / H1) of the maximum axial thickness H2 of the assumed crushed portion V before crushing to the axial thickness H1 of the buffer 50.

[0041] It is preferable that the axial thickness H1 of the buffer 50 be set such that the compressive strain (H2 / H1) of the buffer 50 is less than or equal to the densification initiation strain (1.3 times the plateau stress) measured in JIS H 7902:2016 "Compression Test of Porous Metals". More preferably, the axial thickness H1 of the buffer 50 is set such that the compressive strain (H2 / H1) of the buffer 50 is between 0.2 times and 0.8 times the densification initiation strain. By setting the H2 / H1 range to 0.2 times or more, the buffer 50 can deform sufficiently to absorb the collision energy. Furthermore, by setting the H2 / H1 range to 0.8 times or less, it can be kept generally below the densification initiation stress, thereby suppressing the generation of excessive stress. Although JIS H 7902:2016 "Compression Test for Porous Metals" applies to foamed metals, in this embodiment, it can be applied by a similar test even when wood or foamed resin is used for the buffer 50.

[0042] Furthermore, the buffer body 50 is set such that the volume v of the assumed crushed portion V of the buffer body 50 shown in Figure 6, multiplied by its absorption performance w, is greater than the kinetic energy during the inclined collision shown in Figure 5. The absorption performance w corresponds to the amount of energy absorbed per unit volume as measured in JIS H 7902:2016 "Compression Test of Porous Metals". The kinetic energy represents the sum of the kinetic energy of the cask 11 and the kinetic energy of the surrounding objects S that will be impacted during the collision.

[0043] Furthermore, the buffer body 50 is set such that the axial projected area P × plateau stress of the assumed crushed portion V of the buffer body 50 shown in Figure 6 is smaller than the load capacity of the cask 11. The load capacity of the cask 11 refers to the load at which the cask 11 can maintain its structural integrity and sealing function.

[0044] Figure 7 is an axial view showing a first modified example of the installation range of the axial buffer. Figure 8 is an axial view showing a second modified example of the installation range of the axial buffer.

[0045] In the embodiment described above, the buffer 50 had an annular shape in an axial view, but it may be divided into multiple parts in the circumferential direction and arranged as, for example, the buffer 50A shown in Figure 7. The buffer 50A is arranged so as not to overlap the bolt holes 34 provided on the surface of the lid 13. Alternatively, a notch may be formed in the portion that overlaps the bolt holes 34, as in the buffer 50B shown in Figure 8.

[0046] Although embodiments of this disclosure have been described above, the embodiments are not limited to those described herein.

[0047] [Effects of the Embodiment] The buffer bodies 50, 50A, 50B and the radioactive material storage container described in the embodiment can be understood, for example, as follows.

[0048] The buffers 50, 50A, and 50B according to the first embodiment are installed on the axial end face of a radioactive material storage container (cask 11) having a cask body 12 and a lid 13 that is supported by the flange portion (second stage portion 22b) of the cask body 12 and seals the cask body 12, and in an axial view, the ratio of the area Ad of the coincident area where the installation area and the flange portion coincide to the area Ac of the installation area is 0.8 or more.

[0049] As a result, the buffer 40 can absorb axial impacts to the radioactive material storage container by deforming, ensuring safety even when colliding with the floor F or wall while tilted. In this case, by setting the installation range of the buffers 50, 50A, and 50B in the axial view to the range described above, the flange portion can efficiently receive the reaction force when the buffers 50, 50A, and 50B are crushed. Therefore, the volume of the buffers 50, 50A, and 50B can be reduced, contributing to cost reduction, and the overall weight is reduced, thereby reducing the kinetic energy during impact. In addition, by efficiently receiving the reaction force at the flange portion, excessive loads are suppressed at the sealing boundary between the cask body 12 and the lid portion 13, thereby preventing the integrity of the seal from being compromised. Furthermore, in an axial view, by setting the installation range of the buffers 50, 50A, and 50B to the range described above, the flange portion receives the reaction force when the buffers 50, 50A, and 50B are crushed. As a result, the structure that receives this reaction force does not interfere with the radially positioned buffer material (for example, buffer 40) during a radial collision, thereby preventing interference.

[0050] The buffers 50, 50A, and 50B according to the second embodiment are the buffers 50, 50A, and 50B according to the first embodiment, wherein, in an axial view, the ratio of the area Ad of the matching range to the area Af of the flange portion (second stage portion 22b) is 0.8 or more.

[0051] In an axial view, by setting the installation range of the buffers 50, 50A, and 50B to the range described above, the flange portion can more efficiently receive the reaction force when the buffers 50, 50A, and 50B are crushed.

[0052] The buffers 50, 50A, and 50B according to the third embodiment are buffers 50, 50A, and 50B according to the first or second embodiment, wherein the compressive strain (H2 / H1), which is the ratio of the axial maximum thickness H2 of the assumed crushed portion V, which is the portion cut by a virtual plane VP that is perpendicular to the virtual line VL connecting the corner of the cask body 12 and the center of gravity G of the radioactive material storage container (cask 11) and passes through said corner, to the axial thickness H1, is less than or equal to the densification initiation strain measured in JIS H 7902:2016 "Compression test of porous metals".

[0053] As a result, even if a collision occurs at an angle, that is, if the shock absorbers 50, 50A, and 50B are crushed from a direction inclined with respect to their axial direction, the amount of compressive strain at the time of crushing of the assumed crushed portion V will be less than or equal to the densification initiation strain, thus allowing the impact to be absorbed sufficiently without generating an excessive load.

[0054] The buffers 50, 50A, and 50B according to the fourth embodiment are buffers 50, 50A, and 50B according to any one of the first to third embodiments, wherein the value obtained by multiplying the volume v of the assumed crushed portion, which is the ratio of the axial thickness to the portion cut by a virtual plane perpendicular to the virtual line connecting the corner of the cask body 12 and the center of gravity of the radioactive material container (cask 11) and passing through said corner, by the amount of energy absorbed per unit volume measured in JIS H 7902:2016 "Compression test of porous metals", is greater than the sum of the kinetic energy of the radioactive material container and the kinetic energy of the object of impact S at the time of impact.

[0055] As a result, even if the collision occurs at an angle, that is, if the shock absorbers 50, 50A, and 50B are crushed from a direction inclined with respect to their axial direction, the crushing of the assumed crushed portion V will sufficiently absorb the impact.

[0056] The buffers 50, 50A, and 50B according to the fifth embodiment are buffers 50, 50A, and 50B according to any one of the first to fourth embodiments, wherein the value obtained by multiplying the axial projected area of ​​the assumed crushed portion, which is the portion cut by a virtual plane perpendicular to the virtual line connecting the corner of the cask body 12 and the center of gravity of the radioactive material storage container (cask 11) and passing through said corner, by the plateau stress measured in JIS H 7902:2016 "Compression test of porous metals", is smaller than the load-bearing capacity of the radioactive material storage container.

[0057] As a result, even if a collision occurs at an angle, that is, if the shock absorbers 50, 50A, and 50B are crushed from a direction inclined with respect to their axial direction, the impact can be sufficiently absorbed by the crushing of the assumed crushed portion V. Therefore, it is possible to suppress excessive load on the sealing boundary between the cask body 12 and the lid 13, thereby preventing the integrity of the seal from being compromised.

[0058] The buffers 40, 50, 50A, and 50B according to the sixth embodiment include a radial buffer (buffer 40) that protrudes radially outward from the cask body 12 and is supported on the outer circumferential surface of the cask body 12, and an axial buffer (buffer 50) that protrudes axially outward from the axial end face of the radioactive material storage container (cask 11) and is supported on the end face, wherein the radial buffer and the axial buffer do not come into contact with each other.

[0059] As a result, the buffer 40 absorbs radial impacts to the radioactive material storage container by deforming, and the buffer 50 absorbs axial impacts by deforming, thus ensuring safety even when colliding with the floor F or wall in an inclined state. Furthermore, by arranging the radial buffer and the axial buffer so that they do not come into contact with each other, it is possible to suppress the mutual interference between the deformation of the radial buffer and the deformation of the axial buffer. More specifically, the structure that receives the reaction force when the buffer 40 collapses does not interfere during axial collisions, and the structures that receive the reaction forces when the buffers 50, 50A, and 50B collapse do not interfere during radial collisions, thereby suppressing the mutual interference between their functions.

[0060] The radioactive material storage container (cask 11) according to the seventh embodiment comprises a cask body 12, a lid 13 that seals the cask body 12, and buffers 40, 50, 50A, and 50B according to any one of the first to sixth embodiments.

[0061] As a result, even if the radioactive material storage container is unintentionally dropped or moved during storage, or during transport or handling for storage, and collides with the floor F or wall at an angle, the buffers 40, 50, 50A, and 50B can absorb the axial impact on the container, thereby ensuring safety. [Explanation of Symbols]

[0062] 11 Casks 12 Cask body 13 Lid 22b Second stage section (flange section) 31 Primary lid 32 Secondary lid 33 Tertiary lid 40 Buffer (radial buffer) 50, 50A, 50B buffer (axial buffer) Ac, Ad, Af Area H1 Thickness H2 Maximum Thickness V Assumed crushing area VL virtual line VP virtual plane

Claims

1. It is installed on the axial end face of a radioactive material storage container having a cask body and a lid that is supported by the flange portion of the cask body and seals the cask body, In an axial view, the ratio of the area of ​​the area where the installation area and the flange portion coincide to the area of ​​the installation area is 0.8 or more. buffer body.

2. In an axial view, the ratio of the area of ​​the matching range to the area of ​​the flange portion is 0.8 or more. The buffer according to claim 1.

3. The compressive strain, which is the ratio of the maximum axial thickness of the assumed collapsed portion (the portion cut by a virtual plane perpendicular to and passing through the virtual line connecting the corner of the cask body and the center of gravity of the radioactive material storage container) to the axial thickness, is less than or equal to the densification initiation strain measured in JIS H 7902:2016 "Compression Test of Porous Metals," is The buffer according to claim 1.

4. The value obtained by multiplying the volume of the assumed crushed portion, which is the ratio of the portion cut by a virtual plane perpendicular to and passing through the virtual line connecting the corner of the cask body and the center of gravity of the radioactive material container, with the energy absorption per unit volume measured in JIS H 7902:2016 "Compression Test of Porous Metals", is greater than the sum of the kinetic energy of the radioactive material container and the object being impacted at the time of impact. The buffer according to claim 1.

5. The value obtained by multiplying the axial projected area of ​​the assumed crushed portion, which represents the portion cut by a virtual plane perpendicular to and passing through the virtual line connecting the corner of the cask body and the center of gravity of the radioactive material storage container, with the plateau stress measured in JIS H 7902:2016 "Compression Test of Porous Metals", is smaller than the load-bearing capacity of the radioactive material storage container. The buffer according to claim 1.

6. A radioactive material storage container having a cask body and a lid that seals the cask body, comprising a radial buffer that protrudes radially outward from the cask body and is supported on the outer circumferential surface of the cask body, An axial buffer body is provided which protrudes axially outward from the axial end face of the radioactive material storage container and is supported by the end face, Includes, The radial buffer and the axial buffer do not come into contact with each other. buffer body.

7. The cask itself, The lid portion that seals the cask body, A buffer according to any one of claims 1 to 6, Equipped with, A container for storing radioactive materials.

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