Buffer unit and radioactive material storage container

Abstract

The present invention provides a buffer unit and a radioactive material storage container that can exhibit appropriate cushioning performance against collisions in an inclined state. [Solution] The buffer unit includes a radial buffer and an axial buffer, which are provided on a radioactive material storage container having a cask body and a lid that seals the cask body, and which protrude radially outward from the cask body and are supported on the outer circumferential surface of the cask body. The axial buffer includes a support member which is supported on the axial end face side of the radioactive material storage container and extends radially outward from the inner circumferential surface of the radial buffer in an axial view, and a buffer material which protrudes axially outward so as to cover the surface of the support member.

Description

Technical Field

[0001] The present disclosure relates to a buffer unit and a radioactive material 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 material storage container (cask), transported to a storage facility, reprocessing facility or the like, and stored or reprocessed. The radioactive material storage container is composed of a cylindrical body portion with a bottom and an open top, and a lid portion fixed to the upper part of the body portion to close the opening.

[0003] After transportation, the radioactive material storage container is stored in a storage location for several decades. During storage, the radioactive material storage container is provided with a cushioning material made of steel 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 Invention

Problems to be Solved by the Invention

[0005] However, it is difficult for the cushioning material arranged in the radial direction to secure an effective cushioning material volume when assuming a collision of the radioactive material storage container in an inclined state. On the other hand, when the cushioning material is installed on the axial end face side, a structure that receives a reaction force when the cushioning material is crushed is required, and it is necessary to prevent this structure from interfering 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 an excessive load from entering and impairing the sealing integrity.

[0006] This disclosure aims to solve the aforementioned problems and to provide a buffer unit 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 unit according to one aspect of the present disclosure includes a radial buffer and an axial buffer provided on 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, wherein the axial buffer is provided on the axial end face side of the radioactive material storage container and extends radially outward from the inner circumferential surface of the radial buffer in an axial view, and a buffer material provided protruding axially outward so as to cover the surface of the support member.

[0008] 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]

[0009] 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]

[0010] [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 storage container with a buffer unit installed. [Figure 3] Figure 3 is an axial view showing a radioactive material storage container with a buffer unit installed. [Figure 4] Figure 4 is a front view showing a radioactive material storage container with a buffer unit 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 radial extension of the axial buffer. [Figure 7] Figure 7 is a cross-sectional view showing the main part of a radioactive material storage container fitted with an axial buffer according to the first modified example. [Figure 8] Figure 8 is a graph showing the relationship between deformation and crushing / buckling strength. [Figure 9] Figure 9 is a cross-sectional view showing the main part of a radioactive material storage container fitted with an axial buffer according to the second modified example. [Figure 10] Figure 10 is a graph showing the relationship between deformation and crushing / shear strength. [Figure 11] Figure 11 is a cross-sectional view showing the main part of a radioactive material storage container fitted with an axial buffer according to the third modified example. [Modes for carrying out the invention]

[0011] 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.

[0012] [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.

[0013] As shown in Figure 1, a cask 11 serving as a radioactive substance storage container includes a cask main body 12 and a lid portion 13.

[0014] The cask main 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 is formed with an opening 22 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 substances (for example, spent fuel assemblies). The main body barrel 21 is a forged carbon steel 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.

[0015] The cask main body 12 further includes an outer cylinder 26, heat transfer fins 27, and a resin (neutron shield) 28. The outer cylinder 26 is arranged with a predetermined gap on the outer peripheral surface of the main body barrel 21. 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.

[0016] The cask main 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.

[0017] The cask main 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.

[0018] 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 γ-rays as a material. The secondary lid 32 covers the axially outer side of the primary lid 31, and similarly to the primary lid 31, is formed in a disk shape using carbon steel or stainless steel that shields γ-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 similarly to the primary lid 31 and the secondary lid 32, is formed in a disk shape using carbon steel or stainless steel that shields γ-rays as a material. During storage, the lid part 13 may be provided with an adapter for attaching a buffer body 50 described later instead of the tertiary lid 33.

[0019] The primary lid 31 is fixed to the first step 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 step 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 step portion 22a and between the secondary lid 32 and the second step portion 22b. The metal gaskets ensure the sealing performance between the primary lid 31 and the first step portion 22a and between the secondary lid 32 and the second step portion 22b.

[0020] In the cask main body 12, a cylindrical end edge 22c that surrounds the secondary lid 32 and appears 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 (the upper surface in FIG. 1) at a position on the outer side of the main body cylinder 21 (a higher position in FIG. 1) than the surface of the secondary lid 32, and surrounds the periphery of 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.

[0021] [Buffer unit] Next, an example of the configuration of the buffer unit 1 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 to which the buffer unit is attached. Figure 3 is an axial view showing the radioactive material storage container to which the buffer unit is attached. Figure 4 is a front view showing the radioactive material storage container to which the buffer unit is attached in a horizontal position.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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 cushioning bodies 40 and 50 are attached to the lid 13 side. Alternatively, when storing the cask 11, 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] The buffer 50a is positioned at the end of the cask 11 on the side where the axial lid 13 is provided, so as to cover the surface of the lid 13 and the surface of the edge 22c of the cask body 12. The buffer 50a is positioned at the end of the cask 11 on the side where the axial lid 13 is provided, so as to cover the surface of the tertiary lid 33 or adapter that is exposed on the outside of 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, so as to cover the surface of the bottom 29 and the surface of the edge of the cask body 12. In other words, the buffers 50a and 50b are provided so as to protrude axially outward from the axial end face of the cask 11.

[0031] The buffer 50 is positioned on the outer periphery of the lid 13 and bottom 29 in an axial view, but not in the center. In this embodiment, the buffer 50 has an annular shape in an axial view. Furthermore, the buffer 50 extends radially outward from the inner circumferential surface of the buffer 40 in an axial view. That is, in an axial view, a part of the outer periphery of the buffer 50 and a part of the inner circumferential surface of the buffer 40 overlap. The amount by which the buffer 50 extends radially outward from the inner circumferential surface of the buffer 40 in an axial view (radial extension) will be described in detail later.

[0032] The buffer body 50 comprises a support member 51 and a buffer material 52, which are arranged side by side in the axial direction. In an axial view, the support member 51 and the buffer material 52 are located at the same position. Here, "same" means that dimensional errors are permitted. In this embodiment, the support member 51 and the buffer material 52 are provided with the same shape and dimensions in an axial view, but they do not have to be the same shape and dimensions.

[0033] The support member 51 is made of a metal plate such as a steel plate. The support member 51 is positioned at the end of the cask 11 on the side where the axial lid portion 13 is provided, so as to cover the surface of the lid portion 13 and the surface of the edge 22c of the cask body 12. The support member 51 is positioned at the end of the cask 11 on the side where the axial bottom portion 29 is provided, so as to cover the surface of the bottom portion 29 and the surface of the edge of the cask body 12. In an axial view, the support member 51 is positioned on the outer periphery of the lid portion 13 and the bottom portion 29. In this embodiment, the support member 51 is not positioned at the center of the lid portion 13 and the bottom portion 29 in an axial view, but it may be positioned there. Also, in an axial view, the support member 51 is provided extending radially outward from the inner circumferential surface of the buffer body 40.

[0034] The cushioning material 52 is made of a porous metal such as aluminum, and is deformable under a predetermined load. The cushioning material 52 may be formed as an annular body made of aluminum or the like, with a structure having a plurality of holes that penetrate in the axial direction. The cushioning material 52 is provided so as to protrude outward in the axial direction so as to cover the surface of the support member 51. The cushioning material 52 absorbs the impact by deforming in response to the load applied in the axial direction. At this time, the support member 51 receives the reaction force when the cushioning material 52 deforms due to the impact. The support member 51 separates the cushioning body 40 and the cushioning material 52 in the axial direction of the cask 11. Note that wood or foamed resin may be used as the cushioning material 52.

[0035] 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. If a tertiary cover 33 or adapter is provided as the cover portion 13, the buffer body 50 is positioned along the surface of the tertiary cover 33 or adapter 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.

[0036] [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.

[0037] 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 concrete panels, and they are joined together with bolts or the like for storage.

[0038] 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.

[0039] [Radial extension of the axial buffer] Next, the radial extension amount Ac of the buffer 50 will be explained using Figure 6. Figure 6 is a schematic diagram for explaining the radial extension amount of the axial buffer.

[0040] Here, the radial extension amount Ac of the buffer body 50 is the amount that extends radially outward from the inner circumferential surface of the radial buffer body 40. In other words, the radial extension amount Ac is the radial width of the region where the axial buffer body 50 and the radial buffer body 40 overlap in an axial view. Assuming that the amount of compressive strain when the buffer body 40 is crushed and deformed from the radial outside is the densification initiation strain (1.3 times the plateau stress) measured in JIS H 7902:2016 "Compression Test of Porous Metals", the radial extension amount Ac is set within a range that does not protrude radially outward from the outer circumferential surface of the buffer body 40 after crushing. In other words, the radial extension amount Ac is defined such that the amount of compressive strain of the buffer body 40 when the outer circumferential surface of the buffer body 40 is crushed and deformed up to the outer edge of the support member 51 is greater than the densification initiation strain.

[0041] [Variation] Although embodiments of this disclosure have been described above, the embodiments are not limited to those described herein.

[0042] Figure 7 is a cross-sectional view showing the main part of a radioactive material storage container fitted with an axial buffer according to the first modified example. The right side of Figure 7 shows a cross-sectional view along the axial direction, and the left side shows an end view of the section along line AA shown in the right side. Figure 8 is a graph showing the relationship between deformation and crushing / buckling strength.

[0043] As shown in Figure 7, the axial buffer 50A in the buffer unit 1A of the first modified example has a rib 53 in addition to the support member 51 and the buffer material 52. The rib 53 is interposed between the surface of the lid 13 and the surface of the edge 22c of the cask body 12 and the support member 51 at the end of the cask 11 on the side where the axial lid 13 is provided, and fixes the support member 51 to the main body 21. The rib 53 is interposed between the surface of the bottom 29 and the surface of the edge of the cask body 12 and the support member 51 at the end of the cask 11 on the side where the axial bottom 29 is provided, and fixes the support member 51 to the main body 21.

[0044] The ribs 53 are, for example, thin rods extending radially, and in an axial view, are provided in multiples circumferentially within a range that is radially inward from the outer edge of the buffer body 40 and radially outward from the inner circumferential surface of the support member 51. In the first modified example, eight ribs are provided evenly and at equal intervals in the circumferential direction. The ribs 53 are made of metal or composite material such as carbon steel or FRP (Fiber Reinforced Plastics), and buckle under a predetermined load from the axial direction. The buckling stress of the ribs 53 is greater than the plateau stress of the buffer material 52 measured in JIS H 7902:2016 "Compression test of porous metal".

[0045] As shown in Figure 8, when an axial load is applied, the buffer 50A absorbs the impact energy through the deformation of the ribs 53 and the cushioning material 52, and the buckling of the ribs 53. This suppresses the deformation of the entire buffer 50A, preventing the cushioning material 52 from being unable to absorb the impact and thus preventing excessive load from being placed on the lid 13 and other parts.

[0046] Figure 9 is a cross-sectional view showing the main part of a radioactive material storage container fitted with an axial buffer according to the second modified example. The right side of Figure 9 shows a cross-sectional view along the axial direction, and the left side shows an end view of the BB line section shown in the right side. Figure 10 is a graph showing the relationship between deformation and crush / shear strength.

[0047] As shown in Figure 9, the axial buffer 50B in the second modified buffer unit 1B has a support member 54 instead of the support member 51 in the buffer unit 1 of the embodiment. The support member 54 is provided with an annular shape in axial view, similar to the support member 51 of the embodiment. The support member 54 differs from the support member 51 of the embodiment in that it has a notch 55.

[0048] The notches 55 are, for example, narrow grooves formed along the radial direction, and multiple notches are provided in the circumferential direction. In the second modified example, eight notches are provided evenly and at equal intervals in the circumferential direction. The support member 54 in the second modified example is shear-fractured by a predetermined load applied from the radial direction. In the second modified example, the buffer material 52 is provided so as to cover the surface of the support member 54, including the notches 55. The support member 54 having the notches 55 is shear-fractured by a predetermined load applied from the radial direction. The maximum shear stress of the support member 54 is smaller than the densification initiation stress of the buffer material 40 measured in JIS H 7902:2016 "Compression test of porous metals".

[0049] As shown in Figure 10, when a radial load is applied, the radial buffer 40 first deforms to absorb energy. When the buffer 40 collapses from the radial outside and reaches the outer circumference of the support member 54, the buffer 40 and the support member 54 absorb energy, and the support member 54 is shear-fractured at a predetermined load. When a radial load is applied, if there is no notch 55, the load increases in proportion to the amount of deformation, but because the support member 54 with the notch 55 is shear-fractured, it is possible to suppress the generation of an excessive load on the buffer 50. Furthermore, when a radial load is applied to the buffer 50, the support member 54 is shear-fractured, so an excessive load is not generated on the buffer 50. Therefore, it is not necessary to prevent the buffer 50 from colliding with radial impacts, and the outer diameter of the buffer 50 can be increased.

[0050] Figure 11 is a cross-sectional view showing the main part of a radioactive material storage container fitted with an axial buffer according to the third modified example.

[0051] As shown in Figure 11, the axial buffer 50C in the third modified buffer unit 1C has a support member 56 instead of the support member 51 in the buffer unit 1 of the embodiment. The support member 56 is provided in an annular shape in an axial view, similar to the support member 51 of the embodiment. The support member 56 has a first annular support member 57 that is radially inward and an annular second support member 58 that extends to the outer circumference of the first support member 57.

[0052] The first support member 57 is made of a metal plate such as a steel plate. The first support member 57 is positioned at the end of the cask 11 on the side where the axial lid portion 13 is provided, so as to cover the surface of the lid portion 13 and the surface of the edge 22c of the cask body 12. The first support member 57 is positioned at the end of the cask 11 on the side where the axial bottom portion 29 is provided, so as to cover the surface of the bottom portion 29 and the surface of the edge of the cask body 12. In an axial view, the first support member 57 is provided in a range radially inward from the buffer body 40.

[0053] The second support member 58 is made of a metal such as carbon steel and is provided in a lattice structure in which the axial rigidity is greater than the radial rigidity. In an axial view, the second support member 58 extends radially outward from the inner circumferential surface of the buffer body 40. That is, in an axial view, the second support member 58 and a part of the inner circumferential portion of the buffer body 40 overlap.

[0054] In the third modified example, the buffer body 50C absorbs energy when a radial load is applied by the deformation of the second support member 58, thereby suppressing the inhibition of the deformation of the buffer body 40. Furthermore, when an axial load is applied, the buffer body 50C absorbs the impact by the deformation of the buffer material 52 in response to the axial load. At this time, the first support member 57 and the second support member 58 receive the reaction force when the buffer material 52 deforms due to the impact.

[0055] [Effects of the Embodiment] The buffer units 1, 1A, 1B, 1C and the radioactive material storage container described in the embodiment can be understood, for example, as follows.

[0056] The buffer units 1, 1A, 1B, and 1C according to the first embodiment include a radial buffer (buffer 40) and an axial buffer (buffer 50, 50A, 50B, and 50C) provided on a radioactive material storage container (cask 11) having a cask body 12 and a lid portion 13 that seals the cask body 12, the radial buffer being supported on the outer circumferential surface of the cask body 12 and the axial buffer being provided on the axial end face side of the radioactive material storage container and extending radially outward from the inner circumferential surface of the radial buffer in an axial view, and a buffer material 52 provided that protrudes axially outward so as to cover the surface of the support member 51.

[0057] As a result, the buffer body 40 absorbs radial impacts to the radioactive material storage container by deforming, and the cushioning material 52 absorbs axial impacts by deforming, thus ensuring safety even when colliding with the floor F or wall in an inclined state. In this case, in an axial view, the buffer bodies 50, 50A, 50B, and 50C are provided extending radially outward from the inner circumferential surface of the buffer body 40, and the buffer body 40 and the cushioning material 52 are separated by support members 51, 54, and 56, creating a separate structure. This reduces the overall volume of the buffer body units 1, 1A, 1B, and 1C, contributing to cost reduction and reducing the overall weight, thereby reducing the kinetic energy during impact. Furthermore, the support members 51, 54, and 56 receive the reaction force when the cushioning material 52 is crushed, which suppresses 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. Furthermore, the structure receiving the reaction force does not interfere during radial collisions, thus preventing it from hindering the function of the radially positioned buffer 40.

[0058] The buffer units 1, 1A, 1B, and 1C according to the second embodiment are the buffer units 1, 1A, 1B, and 1C according to the first embodiment, wherein the compressive strain when the radial buffer (buffer 40) deforms in an axial view to the outer peripheral edge of the support members 51, 54, and 56 is greater than the densification initiation strain, which indicates the densification initiation stress measured in JIS H 7902:2016 "Compression Test of Porous Metals".

[0059] As a result, when the deformation of the buffer body 40 reaches the densification initiation strain, the outer edges of the support members 51, 54, and 56 are located radially inward from the outer surface of the buffer body 40. Therefore, when the buffer body 40 is crushed by a radial impact, interference between the support members 51, 54, and 56 can be suppressed.

[0060] The buffer unit 1A according to the third embodiment is a buffer unit 1A according to the first or second embodiment, wherein the axial buffer (buffer 50) is interposed between the axial end face of the radioactive material storage container (cask 11) and the support members 51, 54, and 56, and further has ribs 53 provided radially inward from the outer edge of the radial buffer (buffer 40) in an axial view.

[0061] As a result, before the cushioning material 52 can absorb the impact and an excessive load is placed on the lid 13, etc., the ribs 53 buckle under a predetermined load applied from the axial direction, and the kinetic energy is absorbed by the buckling, thereby suppressing deformation of the entire cushioning body 50A. Therefore, it is possible to prevent the cushioning material 52 from failing to absorb the impact and placing an excessive load on the lid 13, etc., and to prevent an excessive load from being placed on the sealing boundary between the cask body 12 and the lid 13, thereby preventing the integrity of the seal from being compromised.

[0062] The buffer unit 1A according to the fourth embodiment is the buffer unit 1A according to the third embodiment, wherein the buckling load of the rib 53 is greater than the load obtained by the product of the plateau stress of the buffer material 52 measured in JIS H 7902:2016 "Compression test of porous metal" and the projected area of ​​the assumed crushed portion of the buffer material 52 in an axial view.

[0063] This suppresses the initial deformation of the cushioning material 52 during impact and the deformation of the entire cushioning body 50A, thereby preventing excessive load from being applied to the lid 13 and other parts, preventing excessive load from being applied to the sealing boundary between the cask body 12 and the lid 13, and thus preventing the integrity of the seal from being compromised.

[0064] The fifth embodiment of the buffer unit 1B is a buffer unit 1B according to any one of the first to fourth embodiments, wherein the support member 54 has a notch 55 formed along the radial direction.

[0065] As a result, when the radial buffer (buffer 40) is unable to absorb all of the impact energy and a radial load is applied to the support member 54, the support member 54 will be shear-fractured by a predetermined load applied from the radial direction, thereby suppressing the generation of excessive load on the buffer 50B.

[0066] The buffer unit 1B according to the sixth embodiment is the buffer unit 1B according to the fifth embodiment, wherein the maximum shear load of the support member 54 is smaller than the load obtained by the product of the densification initiation stress of the radial buffer (buffer 40) measured in JIS H 7902:2016 "Compression test of porous metals" and the projected area of ​​the assumed crushed portion of the buffer 40 in the radial view.

[0067] As a result, when the buffer body 40 is crushed by a radial impact and a radial load is applied to the support member 54, the support member 54 is immediately sheared and broken, thereby preventing the generation of excessive load on the buffer body 50B.

[0068] The seventh embodiment of the buffer unit 1C is a buffer unit 1C according to any one of the first to sixth embodiments, wherein the support member 56 includes a first support member 57 provided in an axial view within a range radially inward from the radial buffer (buffer 40), and a second support member 58 extending radially outward from the inner circumferential surface of the radial buffer in an axial view, and provided on a lattice structure whose axial rigidity is greater than its radial rigidity.

[0069] As a result, the second support member 58 can deform with low loads under radial loads, suppressing the generation of excessive loads, and is less prone to deformation under axial loads, allowing it to receive the reaction force of the axial buffer (buffer 50).

[0070] The radioactive material storage container (cask 11) according to the eighth embodiment comprises a cask body 12, a lid 13 that seals the cask body 12, and buffer units 1, 1A, 1B, 1C (buffer 40 and buffers 50, 50A, 50B, 50C) according to any one of the first to sixth embodiments.

[0071] This ensures safety because, even if the radioactive material storage container is unintentionally dropped or moved during storage and collides with the floor F or wall at an angle, the buffer can absorb the radial and axial impact to the container. [Explanation of Symbols]

[0072] 1, 1A, 1B, 1C Buffer Unit 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, 50C buffer (axial buffer) 51, 54, 56 Support members 52 Cushioning material 53 Ribs 55 Notch 57 First support member 58 Second support member Ac Radial extension amount

Claims

1. 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, Axial buffer and Includes, The axial buffer body is A support member is provided that is supported on the axial end face side of the radioactive material storage container and extends radially outward from the inner circumferential surface of the radial buffer in an axial view, A cushioning material is provided that protrudes outward in the axial direction so as to cover the surface of the support member, Having, Buffer unit.

2. The radial buffer body, when deformed in an axial view, such that the amount of compressive strain when the outer surface extends to the outer edge of the support member is greater than the densification initiation strain, which indicates the densification initiation stress measured in JIS H 7902:2016 "Compression Test of Porous Metals", The buffer unit according to claim 1.

3. The axial buffer body is The radioactive material storage container has a rib interposed between its axial end face and the support member, and which, in an axial view, is provided radially inward from the outer edge of the radial buffer. The buffer unit according to claim 1.

4. The buckling load of the rib is greater than the load obtained by the product of the plateau stress of the buffer material measured in JIS H 7902:2016 "Compression Test of Porous Metals" and the projected area of ​​the assumed crushed portion of the buffer material in an axial view. The buffer unit according to claim 3.

5. The aforementioned support member is Having a notch formed along the radial direction, The buffer unit according to claim 1.

6. The maximum shear load of the support member is less than the load obtained by the product of the densification initiation stress of the radial buffer, measured in JIS H 7902:2016 "Compression Test of Porous Metals," and the radially projected area of ​​the assumed crushed portion of the radial buffer. The buffer unit according to claim 5.

7. The aforementioned support member is A first support member provided in a region radially inward from the radial buffer in an axial view, A second support member is provided on a lattice structure that extends radially outward from the inner circumferential surface of the radial buffer in an axial view, and whose axial rigidity is greater than its radial rigidity. Having, The buffer unit according to claim 1.

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

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