Storage buffer structure

Abstract

To improve the heat removal performance of a cushioning structure for storage.SOLUTION: A spacer 24 of a cushioning structure 2 is fixed to a first cushioning portion 21 and a second cushioning portion 22. The spacer 24 is arranged between the first cushioning portion 21 and a cask end surface 11, and a first flow passage 34 enabling gas to pass therethrough is formed between the first cushioning portion 21 and the cask end surface 11. Also, the spacer 24 is arranged between the second cushioning portion 22 and a cask side surface 12, and a second flow passage 35 enabling gas to pass therethrough is formed between the second cushioning portion 22 and the cask side surface 12. The second flow passage 35 is communicated with the first flow passage 34. Herewith, the heat removal performance of the cushioning structure 2 can be improved.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a storage buffer structure that is attached to the end of a cask during storage. [Background technology]

[0002] Conventionally, spent fuel used in nuclear reactors, etc. is stored in cooling pools installed within nuclear power plants until the radiation level drops below a predetermined level, and then placed in casks with shielding and sealing functions, etc., and transported to interim storage facilities, fuel reprocessing facilities, etc. During cask transportation, buffer structures are attached to the upper and lower ends of the cask to maintain the shielding and sealing functions, etc., of the cask in the unlikely event of a fall accident, etc.

[0003] For example, in the cask of Patent Document 1, a tertiary transport lid and a transport buffer are attached to the outside of the primary and secondary lids attached to the ends of the cask, thereby maintaining the cask's sealing properties and impact resistance during transportation. Furthermore, in this cask, when storing radioactive material, a tertiary storage lid is attached to the end of the cask instead of the tertiary transport lid and the transport buffer. The tertiary storage lid prevents flying objects from directly colliding with the secondary lid in the event of an aircraft accident, etc. Furthermore, a circular, enclosed space is provided between the tertiary storage lid and the secondary lid, which prevents the tertiary storage lid from coming into contact with the secondary lid even if flying objects collide with the tertiary storage lid and deform it. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6324139 Summary of the Invention [Problem to be solved by the invention]

[0005] The transportation tertiary lid and transportation buffer in Patent Document 1 are temporarily attached to the cask, and therefore are not significantly affected by the heat from the cask. On the other hand, the storage tertiary lid is attached to the cask for a long period of time, and therefore is subject to a large thermal effect from the high-temperature cask, which may result in a deterioration of buffer performance. As mentioned above, a disk-shaped closed space exists between the storage tertiary lid and the secondary lid. While this space causes an initial delay in heat transfer, it does little to reduce the long-term thermal effect.

[0006] The present invention has been made in consideration of the above-mentioned problems, and aims to improve the heat removal performance of a storage cushioning structure. [Means for solving the problem]

[0007] A first aspect of the present invention is a storage buffer structure that is fitted to the end of a cylindrical cask that contains fuel assemblies during storage, and includes a first buffer section that faces but is spaced apart from the cask end face, which is the longitudinal end face of the cask, and extends radially outward from the outer peripheral edge of the cask end face; a cylindrical second buffer section that extends longitudinally from the first buffer section along the cask side face, which is the side face of the cask, radially outward from the outer peripheral edge of the cask end face, and faces but is spaced apart from the cask side face in the radial direction; and a spacer that is arranged between the first buffer section and the cask end face, forming a first flow path through which gas can pass between the first buffer section and the cask end face, and that is arranged between the second buffer section and the cask side face, forming a second flow path through which gas communicating with the first flow path can pass between the second buffer section and the cask side face.

[0008] The invention of aspect 2 is a storage buffer structure of aspect 1, wherein the spacer has a plurality of ribs arranged radially in the circumferential direction, and each of the plurality of ribs has a plate-shaped first rib portion extending radially between the first buffer portion and the cask end face and perpendicular to the cask end face, and a plate-shaped second rib portion continuing from the radial outer end of the first rib portion and extending longitudinally between the second buffer portion and the side surface of the cask, and in each two circumferentially adjacent ribs among the plurality of ribs, the gap between the first rib portions of each of the two ribs is the first flow path, and the gap between the second rib portions of each of the two ribs is the second flow path.

[0009] A third aspect of the invention is the storage buffer structure of the second aspect, wherein each of the plurality of ribs has a through hole penetrating in the thickness direction, or a notch on the edge that comes into contact with the cask.

[0010] The invention of aspect 4 is a storage buffer structure of aspect 1, wherein the cask is placed with its longitudinal direction horizontal, and the spacer has a plurality of ribs arranged horizontally, each of the plurality of ribs having a plate-shaped first rib portion extending along the direction of gravity between the first buffer portion and the end face of the cask and perpendicular to the end face of the cask, and a plate-shaped second rib portion continuing from one end of the first rib portion in the direction of gravity and extending along the longitudinal direction between the second buffer portion and the side face of the cask, and wherein for each two horizontally adjacent ribs among the plurality of ribs, the gap between the first rib portions of each of the two ribs is the first flow path, and the gap between the second rib portions of each of the two ribs is the second flow path.

[0011] The invention of aspect 5 is a storage buffer structure of aspect 4, further comprising a plurality of side ribs on each of the left and right sides of the second buffer section, which are perpendicular to the direction of gravity and the longitudinal direction, that extend upward in the direction of gravity as they move from one side to the other in the longitudinal direction between the second buffer section and the side of the cask, and are fixed to the second buffer section and contact the side of the cask, and the gaps between the plurality of side ribs are side flow paths that communicate with the space between the first buffer section and the end face of the cask.

[0012] The invention of aspect 6 is a storage buffer structure of aspect 4 (which may also be aspect 4 or 5), in which each of the multiple ribs has a through hole penetrating in the thickness direction, or a notch is provided on the edge that comes into contact with the cask.

[0013] The invention of aspect 7 is a storage buffer structure of aspect 1 (which may be any one of aspects 1 to 6), further comprising a plate-shaped fin protruding toward the cask from at least one of the surfaces of the first buffer portion facing the end surface of the cask and the surface of the second buffer portion facing the side surface of the cask.

[0014] The invention of aspect 8 is a storage buffer structure of aspect 1, wherein the spacer comprises a plurality of first convex portions that are spaced apart and distributed over the entire inner surface of the first buffer portion, which is the surface of the first buffer portion facing the cask end surface, and that protrude toward the cask end surface, and a plurality of second convex portions that are spaced apart and distributed over the entire inner surface of the second buffer portion, which is the surface of the second buffer portion facing the cask side surface, and that protrude toward the cask side surface, and the space between the plurality of first convex portions is the first flow path, and the space between the plurality of second convex portions is the second flow path.

[0015] A ninth aspect of the invention is a storage buffer structure according to any one of the first to eighth aspects, wherein a third flow path is provided that extends from the first flow path or the second flow path and penetrates the first buffer section or the second buffer section.

[0016] A tenth aspect of the invention is a storage buffer structure that is fitted to the end of a cylindrical cask that contains fuel assemblies during storage of the cask, and includes a first buffer section that faces a cask end face, which is the end face in the longitudinal direction of the cask, and extends radially outward from an outer circumferential edge of the cask end face, and a cylindrical second buffer section that extends radially outward from the outer circumferential edge of the cask end face from the first buffer section along a cask side face, which is the side face of the cask, and faces the cask side face in the radial direction; A spacer is disposed between the first buffer section and the end surface of the cask, a first flow path through which gas can pass is formed between the first buffer section and the end surface of the cask; A spacer is disposed between the second buffer section and the side surface of the cask, A second flow path through which gas can pass is formed between the second buffer portion and the side surface of the cask, and a third flow path is provided extending from the first flow path or the second flow path and penetrating the first buffer portion or the second buffer portion.

[0017] The invention of aspect 11 is a storage buffer structure of aspect 1 or 10 (or any one of aspects 1 to 10), wherein at least one of the first buffer section and the second buffer section comprises a buffer material, an outer wall covering the outer surface of the buffer material, and an insulating material arranged between the outer wall and the buffer material at a position facing the cask and having a lower thermal conductivity than the outer wall.

[0018] The invention of aspect 12 is a storage buffer structure of aspect 1 or 10 (which may be any one of aspects 1 to 11), wherein the first buffer section is a cylindrical section with a through hole in the radial center, and the storage buffer structure further includes a cover member that is attached inside the through hole to block the through hole and that faces the cask end face in the longitudinal direction at the same longitudinal position as the surface of the first buffer section that faces the cask end face. [Effects of the Invention]

[0019] The present invention can improve the heat removal performance of a storage cushioning structure. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a plan view of a cushioning structure according to a first embodiment. [Figure 2] FIG. 2 is a vertical cross-sectional view of the cushioning structure. [Figure 3] FIG. 2 is a vertical cross-sectional view of the cushioning structure. [Figure 4] FIG. 2 is a vertical cross-sectional view of the cushioning structure. [Figure 5] FIG. [Figure 6] FIG. 2 is a vertical cross-sectional view of the cushioning structure. [Figure 7] FIG. 2 is a vertical cross-sectional view of the cushioning structure. [Figure 8] FIG. 10 is a front view of a cushioning structure according to a second embodiment. [Figure 9] FIG. 10 is a side view of a side rib. [Figure 10] FIG. 10 is a plan view of a cushioning structure according to a third embodiment. [Figure 11] FIG. 2 is a vertical cross-sectional view of the cushioning structure. [Figure 12] FIG. 10 is a longitudinal cross-sectional view of a cushioning structure according to a fourth embodiment. [Figure 13] FIG. 2 is a vertical cross-sectional view of the cushioning structure. DETAILED DESCRIPTION OF THE INVENTION

[0021] Fig. 1 is a plan view showing a storage buffer structure 2 according to a first embodiment of the present invention. Fig. 2 is a longitudinal cross-sectional view of the storage buffer structure 2 taken along line II-II in Fig. 1. Figs. 1 and 2 also show a portion of a cask 1 to which the buffer structure 2 is attached. The buffer structure 2 reduces impact loads such as tipping over of the cask 1 during storage.

[0022] The cask 1 is a columnar container capable of accommodating spent fuel assemblies (hereinafter simply referred to as "fuel assemblies"). The cask 1 is approximately cylindrical, centered on a central axis J1 extending in the vertical direction in FIG. 2. The cask 1 has a shielding function for shielding against radiation, a sealing function for sealing in radioactive materials, a subcriticality maintenance function for maintaining the fuel assemblies in a subcritical state, and a heat removal function for dissipating heat from the fuel assemblies.

[0023] When the cask 1 is stored in an interim storage facility or the like, the cask 1 is stored in an upright position with the central axis J1 facing the direction of gravity (so-called vertical placement), or in a laid-down position with the central axis J1 facing horizontally (so-called horizontal placement). In this embodiment, the case where the cask 1 is stored in an upright position is described. The direction in which the central axis J1 of the cask 1 extends is called the "longitudinal direction," and in Figure 2, the longitudinal direction is approximately the same as the direction of gravity.

[0024] 1 and 2 also show the vicinity of the upper end of the upright cask 1. The storage buffer structure 2 (hereinafter simply referred to as the "buffer structure 2") is attached to the upper end of the upright cask 1 when the cask 1 is stored. Note that the buffer structure 2 is not attached to the lower end of the cask 1.

[0025] The buffer structure 2 is a structure in which the outer surface of a buffer material 31 is covered with an outer wall 32 (i.e., a casing). The buffer material 31 is made of, for example, a rigid foam resin such as rigid polyurethane foam, or wood. The buffer material 31 may be made of other materials (e.g., foam metal). The outer wall 32 is, for example, a metal plate such as stainless steel. In the example shown in FIG. 2, the outer wall 32 covers the entire outer surface of the buffer material 31, but this is not limited to this. The outer wall 32 may cover only a portion of the outer surface of the buffer material 31 (e.g., a portion of the buffer material 31 that faces the cask 1). In FIG. 2, the outer wall 32 is indicated by a thick solid line. This also applies to FIGS. 3, 4, 6, 7, 9, and 11, which will be described later.

[0026] In the example shown in FIG. 2 , a thermal insulator 33 is provided between the outer wall 32 and the buffer material 31 in the portion of the buffer structure 2 facing the cask 1. The thermal insulator 33 is a material having a lower thermal conductivity than the outer wall 32. For example, a ceramic-based thermal insulator can be used as the thermal insulator 33. Note that the thermal insulator 33 does not necessarily have to be provided over the entire portion of the buffer structure 2 facing the cask 1, and may be provided over only a portion of that portion. Alternatively, the thermal insulator 33 may also be provided in a portion of the buffer structure 2 that does not face the cask 1.

[0027] The buffer structure 2 includes a first buffer section 21, a second buffer section 22, and a spacer 24. The first buffer section 21 and the second buffer section 22 are a continuous member. In the following description, the first buffer section 21 and the second buffer section 22 are collectively referred to as the "buffer body 20." In FIG. 2, the boundary between the first buffer section 21 and the second buffer section 22 in the buffer body 20 is indicated by a two-dot chain line. This boundary is a substantially circular ring shape centered on the central axis J1. The buffer body 20 is a substantially cylindrical member centered on the central axis J1. The first buffer section 21 and the second buffer section 22 are also each a substantially cylindrical portion centered on the central axis J1. In the following description, the through-hole provided in the center of the first buffer section 21 in the radial direction (i.e., the radial direction centered on the central axis J1) is also referred to as the "central space 211." In plan view, the diameter of the central space 211 is, for example, 40% to 60% of the outer diameter of the first buffer section 21.

[0028] The first buffer section 21 is located above the cask 1, and the lower surface of the first buffer section 21 faces, but is spaced apart from, the cask end surface 11 (i.e., the upper end surface), which is one of the longitudinal end surfaces of the cask 1. In plan view, the inner diameter of the first buffer section 21 is smaller than the diameter of the cask end surface 11, and the outer diameter of the first buffer section 21 is larger than the diameter of the cask end surface 11. In other words, in plan view, the first buffer section 21 partially overlaps the cask end surface 11 and extends radially outward beyond the outer circumferential edge of the cask end surface 11.

[0029] The second buffer section 22 extends downward (i.e., downward in the longitudinal direction) from the outer peripheral edge of the first buffer section 21, radially outward of the outer peripheral edge of the cask end face 11. The second buffer section 22 extends along the cask side surface 12, which is the side surface of the cask 1, to a position below the cask end face 11. The second buffer section 22 surrounds the entire periphery of the cask 1 in the circumferential direction (i.e., the circumferential direction centered on the central axis J1), and the inner surface of the second buffer section 22 faces the cask side surface 12 while being spaced apart in the radial direction. The longitudinal length of the second buffer section 22 is, for example, 30% to 70% of the longitudinal length of the first buffer section 21.

[0030] Near the inner surface of the second buffer section 22, a substantially cylindrical heat insulating material 33 is provided between the outer wall 32 and the buffer material 31. In addition, in the first buffer section 21, near the lower surface of a portion located radially inward from the inner surface of the second buffer section 22, a substantially annular plate-shaped heat insulating material 33 is provided between the outer wall 32 and the buffer material 31. In the example shown in FIG. 2 , the outer peripheral edge portion of the heat insulating material 33 provided in the first buffer section 21 and the upper end portion of the heat insulating material 33 provided in the second buffer section 22 are continuous.

[0031] The spacer 24 is disposed between the cask 1 and the first buffer section 21 and the second buffer section 22, and separates the cask 1 from the first buffer section 21 and the second buffer section 22. The spacer 24 is fixed to the lower surface of the first buffer section 21 and the inner surface of the second buffer section 22. The spacer 24 partially overlaps the lower surface of the first buffer section 21 in a plan view, radially inward from the inner surface of the second buffer section 22, but does not overlap the entire lower surface. Furthermore, the spacer 24 does not overlap the entire inner surface of the second buffer section 22, but is provided partially on the inner surface.

[0032] In this embodiment, the spacer 24 includes a plurality of ribs 241 arranged radially in the circumferential direction. In the example shown in FIG. 1 , 16 ribs 241 are arranged spaced apart from one another at approximately equal angular intervals (i.e., at intervals of approximately 22.5°) in the circumferential direction. Each rib 241 is a substantially flat plate-shaped member extending substantially linearly in the radial direction in a plan view. The ribs 241 are formed of a metal such as stainless steel, aluminum, or copper-clad aluminum. The material of the ribs 241 may be the same as or different from the material of the outer wall 32 of the buffer main body 20. The number of ribs 241 may be changed as appropriate, and the material of the ribs 241 may be other than metal. Furthermore, the plurality of ribs 241 do not necessarily need to be arranged at approximately equal angular intervals, but may also be arranged at unequal angular intervals in the circumferential direction.

[0033] 3 is a longitudinal cross-sectional view of the buffer structure 2 taken along line III-III in FIG. 1. The rib 241 shown in FIG. 3 includes a first rib portion 41 and a second rib portion 42. The first rib portion 41 is a substantially flat portion that is substantially perpendicular to the cask end surface 11 and extends substantially linearly in the radial direction between the lower surface of the first buffer portion 21 and the cask end surface 11. The first rib portion 41 is fixed to the lower surface of the first buffer portion 21, and the lower end of the first rib portion 41 contacts the cask end surface 11. The first rib portion 41 supports the weight of the buffer main body 20 on the cask end surface 11. The height of the first rib portion 41 in the longitudinal direction is, for example, 30 mm to 70 mm.

[0034] The first rib portion 41 extends from between the lower surface of the first buffer portion 21 and the cask end face 11 to a position radially inward beyond the inner surface of the first buffer portion 21. In other words, the radially inner end of the first rib portion 41 protrudes radially inward from the inner surface of the first buffer portion 21 into the central space 211 in a plan view. The radially outer end of the first rib portion 41 is located at approximately the same radial position as the cask side surface 12. Note that the first rib portion 41 may extend from between the lower surface of the first buffer portion 21 and the cask end face 11 to a position radially outward beyond the outer circumferential edge of the cask end face 11.

[0035] The second rib portion 42 is a substantially flat portion that is substantially perpendicular to the cask side surface 12 (i.e., perpendicular to the tangent to the cask side surface 12 at the contact portion with the cask side surface 12), and extends substantially linearly along the longitudinal direction between the inner surface of the second buffer portion 22 and the cask side surface 12. The second rib portion 42 is fixed to the inner surface of the second buffer portion 22, and the radially inner end of the second rib portion 42 contacts the cask side surface 12. The radial width of the second rib portion 42 is, for example, 30 mm to 70 mm. The radial width of the second rib portion 42 is, for example, substantially the same as the height of the first rib portion 41 in the longitudinal direction.

[0036] The lower end of the second rib portion 42 is located at approximately the same position in the longitudinal direction as the lower end of the second buffer portion 22. The second rib portion 42 may extend from between the inner surface of the second buffer portion 22 and the cask side surface 12 to a position lower than the lower end of the second buffer portion 22. The second rib portion 42 extends from between the inner surface of the second buffer portion 22 and the cask side surface 12 to a position higher than the cask end surface 11, and the upper end of the second rib portion 42 is continuous with the radial outer end of the first rib portion 41. In other words, the rib 241 is a member that is approximately L-shaped in side view.

[0037] 1, of the 16 ribs 241, eight ribs 241 arranged at intervals of approximately 45° have substantially the same shape as that shown in FIG. 3. The remaining eight ribs 241 have substantially the same shape as that shown in FIG. 3, except that the inner ends of the first rib portions 41 are positioned at substantially the same radial position as the inner surface of the first buffer section 21. In other words, in the remaining eight ribs 241, the radially inner ends of the first rib portions 41 do not protrude radially inward from the inner surface of the first buffer section 21.

[0038] Focusing on two circumferentially adjacent ribs 241 among the multiple ribs 241, the space surrounded by the first rib portions 41 of the two ribs 241, the lower surface of the first buffer section 21, and the cask end face 11 is a first flow path 34 through which gas can pass. The first flow path 34 is the gap between the first rib portions 41 of the two ribs 241, and extends radially outward from the central space 211 between the lower surface of the first buffer section 21 and the cask end face 11 to reach the inner surface of the second buffer section 22.

[0039] The space surrounded by the second rib portions 42 of the two ribs 241, the inner surface of the second buffer portion 22, and the cask side surface 12 is a second flow path 35 through which gas can pass. The second flow path 35 is a gap between the second rib portions 42 of the two ribs 241, and extends upward from the lower end of the second buffer portion 22 to the lower surface of the first buffer portion 21 between the inner surface of the second buffer portion 22 and the cask side surface 12. The upper end of the second flow path 35 is connected to the radially outer end of the first flow path 34. As a result, the first flow path 34 and the second flow path 35 communicate with each other to form a single flow path (hereinafter also referred to as a "communicating flow path 30"). The communicating flow path 30 extends upward along the cask side surface 12 and radially inward along the cask end surface 11 to reach the central space 211.

[0040] 1 and 2, among the 16 ribs 241, in each two ribs 241 adjacent to each other in the circumferential direction, the gap between the first rib portions 41 of each of the two ribs 241 forms the first flow path 34, and the gap between the second rib portions 42 of each of the two ribs 241 forms the second flow path 35 that communicates with the first flow path 34. As a result, 16 communicating flow paths 30 are provided between the cask 1 and the buffer body 20 of the buffer structure 2, arranged in the circumferential direction.

[0041] Heat dissipated from the portion of the upper end of the cask 1 covered by the buffer structure 2 is imparted to gas (e.g., air) present between the buffer structure 2 and the cask 1, causing the gas to heat up. The heated gas between the second buffer 22 and the cask side surface 12 moves upward in the second flow path 35 due to a decrease in density. As a result, an airflow is formed in the communication flow path 30, rising in the second flow path 35 and flowing radially inward through the first flow path 34 toward the central space 211. Therefore, the gas heated between the first buffer 21 and the cask end surface 11 also moves radially inward in the first flow path 34 together with the airflow and is dissipated into the space above the buffer structure 2 via the central space 211. This prevents high-temperature gas from accumulating between the cask 1 and the buffer structure 2, improving the heat removal performance of the buffer structure 2 (i.e., the ability to remove heat from the cask 1 and dissipate it to the surroundings). As a result, the temperature rise of the buffer structure 2 is suppressed, and the deterioration of the buffer performance of the buffer structure 2 due to the thermal influence on the buffer material 31 and the like is suppressed.

[0042] It should be noted that the number of the multiple ribs 241 in the buffer structure 2 may be changed as appropriate. In each rib 241, the first rib portion 41 does not necessarily have to extend in the radial direction, but may extend along the radial direction while inclining relative to the radial direction (for example, while inclining at an inclination angle of 30° or less). Furthermore, the second rib portion 42 does not necessarily have to extend in the longitudinal direction, but may extend along the longitudinal direction while inclining relative to the longitudinal direction (for example, while inclining at an inclination angle of 30° or less). Each of the first rib portion 41 and the second rib portion 42 does not necessarily have to extend in a substantially straight line, but may extend while curved.

[0043] As shown in FIG. 3, the rib 241 has notches 242 on the edge that comes into contact with the cask 1. In the example shown in FIG. 3, a plurality of notches 242 are provided on the lower edge of the first rib portion 41, spaced apart from one another in the radial direction. Furthermore, a plurality of notches 242 are provided on the inner edge of the second rib portion 42, spaced apart from one another in the longitudinal direction. This allows each pair of circumferentially adjacent communication channels 30 to communicate with each other via the plurality of notches 242. This improves the circumferential temperature uniformity of the high-temperature gas between the buffer structure 2 and the cask 1. As a result, heat from the cask 1 is efficiently dissipated approximately uniformly in the circumferential direction, further improving the heat removal performance of the buffer structure 2.

[0044] In the example shown in Fig. 3, the shape of the notch 242 when viewed in the circumferential direction is approximately semicircular, but this shape may be modified in various ways. Furthermore, the sizes of the multiple notches 242 are approximately the same, but may be different. The number and arrangement of the notches 242 provided in the rib 241 may also be modified in various ways. For example, the notches 242 may be provided only in the first rib portion 41 or the second rib portion 42. Furthermore, the number of notches 242 provided in each rib 241 may be one, or two or more.

[0045] In the rib 241, instead of or in addition to the notches 242, through holes may be provided that penetrate the rib 241 in the circumferential direction (i.e., the thickness direction of the rib 241). In the example shown in FIG. 4, a plurality of through holes 243, the same number as the plurality of notches 242 shown in FIG. 3, are provided in the first rib portion 41 and the second rib portion 42 of the rib 241 instead of the plurality of notches 242. In this case, similarly to the case where the notches 242 are provided, each two circumferentially adjacent communication channels 30 communicate with each other via the through holes 243, thereby improving the temperature uniformity of the gas between the buffer structure 2 and the cask 1 in the circumferential direction. As a result, the heat removal performance of the buffer structure 2 is further improved.

[0046] 4, the shape of the through holes 243 when viewed in the circumferential direction is substantially circular, but this shape may be modified in various ways. Furthermore, the sizes of the multiple through holes 243 are substantially the same, but may be different. The number and arrangement of the through holes 243 provided in the rib 241 may also be modified in various ways. For example, the through holes 243 may be provided only in the first rib portion 41 or the second rib portion 42. Furthermore, the number of through holes 243 provided in each rib 241 may be one, or two or more.

[0047] 1 and 2, the buffer structure 2 is provided with a plurality of third flow paths 36. In the example shown in Fig. 1, the same number of third flow paths 36 as the plurality of communication flow paths 30 (i.e., 16) are arranged at approximately equal angular intervals in the circumferential direction. Each third flow path 36 is arranged between the first rib portions 41 of two ribs 241 adjacent to each other in the circumferential direction.

[0048] In the example shown in FIG. 2, the third flow path 36 extends upward in a substantially linear manner from the upper end of the first flow path 34 along the direction of gravity (i.e., the longitudinal direction) and penetrates the first buffer section 21. The third flow path 36 guides the high-temperature gas in the first flow path 34 upward and dissipates it into the space above the buffer structure 2. This promotes the release of the high-temperature gas between the buffer structure 2 and the cask 1 to the outside, further improving the heat removal performance of the buffer structure 2. In the example shown in FIG. 1, the cross-sectional shape of the third flow path 36 perpendicular to the longitudinal direction is, for example, substantially circular. The cross-sectional shape may be modified in various ways.

[0049] In the buffer structure 2, the number and arrangement of the third flow paths 36 may be modified in various ways. For example, the third flow path 36 may be disposed vertically above the second flow path 35, extend upward in a substantially straight line in the direction of gravity from the upper end of the connection between the first flow path 34 and the second flow path 35, and penetrate the first buffer section 21. In this case, the third flow path 36 guides the high-temperature gas in the first flow path 34 and the second flow path 35 upward and dissipates it into the space above the buffer structure 2. This promotes the release of high-temperature gas between the buffer structure 2 and the cask 1 to the outside, further improving the heat removal performance of the buffer structure 2.

[0050] Furthermore, the third flow paths 36 do not necessarily need to extend along the direction of gravity, but may extend obliquely upward from the first flow paths 34 and penetrate the first buffer section 21. Alternatively, the third flow paths 36 may extend substantially horizontally or obliquely upward from the second flow paths 35 and penetrate the second buffer section 22. In the buffer structure 2, the multiple third flow paths 36 do not necessarily need to be arranged at substantially equal angular intervals, but may be arranged at unequal angular intervals in the circumferential direction. The number of third flow paths 36 provided in the buffer structure 2 may be one, or two or more. The same applies to the third flow paths 36a described below.

[0051] As described above, the storage buffer structure 2 (i.e., the buffer structure 2) is attached to the end of the cylindrical cask 1 during storage of the cask 1 accommodating fuel assemblies. The buffer structure 2 includes a first buffer 21, a second buffer 22, and a spacer 24. The first buffer 21 faces the cask end face 11, which is the longitudinal end face of the cask 1, while being spaced apart in the longitudinal direction. The first buffer 21 extends radially outward beyond the outer circumferential edge of the cask end face 11. The second buffer 22 extends radially outward beyond the outer circumferential edge of the cask end face 11, from the first buffer 21 along the cask side face 12, which is the side face of the cask 1. The second buffer 22 is a cylindrical portion facing the cask side face 12 while being spaced apart in the radial direction.

[0052] The spacer 24 is disposed between the first buffer 21 and the cask end surface 11, and forms a first flow path 34 through which gas can pass between the first buffer 21 and the cask end surface 11. The spacer 24 is also disposed between the second buffer 22 and the cask side surface 12, and forms a second flow path 35 through which gas can pass between the second buffer 22 and the cask side surface 12. The second flow path 35 communicates with the first flow path 34.

[0053] As a result, as described above, the high-temperature gas heated by the cask 1 can be dissipated from between the buffer structure 2 and the cask 1 to the outside via the first flow path 34 and the second flow path 35, which are connected to each other, thereby improving the heat removal performance of the buffer structure 2. This suppresses the temperature rise of the buffer structure 2 and reduces the thermal impact on the buffer material 31, etc. As a result, it is possible to suppress the deterioration of the buffer performance of the buffer structure 2 due to the thermal impact. Furthermore, it is possible to suppress the temperature rise of the cask 1 and suppress the deterioration of the gaskets and neutron shielding of the cask 1. As a result, it is also possible to suppress the deterioration of the sealing performance and shielding performance of the cask 1.

[0054] As described above, the spacer 24 preferably includes a plurality of ribs 241 arranged radially in the circumferential direction. Each of the plurality of ribs 241 includes a first rib portion 41 extending radially between the first buffer portion 21 and the cask end surface 11, and a second rib portion 42 extending longitudinally between the second buffer portion 22 and the cask side surface 12. The first rib portion 41 is a plate-shaped portion perpendicular to the cask end surface 11. The second rib portion 42 is a plate-shaped portion continuous with the radially outer end of the first rib portion 41. Among the plurality of ribs 241, for each pair of circumferentially adjacent ribs 241, the gap between the first rib portions 41 of the pair of ribs 241 is the first flow path 34, and the gap between the second rib portions 42 of the pair of ribs 241 is the second flow path 35.

[0055] In this way, by dividing the space between the buffer structure 2 and the cask 1 into a plurality of communicating passages 30 using the plurality of plate-like ribs 241, it is possible to increase the volume of each communicating passage 30 (i.e., the volume of each of the first passages 34 and each of the second passages 35). As a result, it is possible to increase the flow rate of high-temperature gas flowing between the buffer structure 2 and the cask 1, and further improve the heat removal performance of the buffer structure 2.

[0056] As described above, the ribs 241 are preferably made of metal. This allows the ribs 241 to function effectively as heat dissipation fins, and allows heat transferred from the cask 1 to the ribs 241 to be efficiently dissipated from the surfaces of the ribs 241 into the surrounding gas. This reduces the heat transferred to the buffer body 20 (i.e., the first buffer section 21 and the second buffer section 22) via the ribs 241. As a result, the heat removal performance of the buffer structure 2 can be further improved, and a decrease in the buffer performance of the buffer structure 2 due to thermal influences can be further suppressed. From the viewpoint of improving the fin efficiency of the ribs 241 and further improving the heat removal performance of the buffer structure 2, the material of the ribs 241 is preferably aluminum or copper-clad aluminum, which have high heat dissipation properties.

[0057] As described above, each of the plurality of ribs 241 preferably has a notch 242 on the side that contacts the cask 1, or a through-hole 243 that penetrates in the thickness direction. This improves the circumferential temperature uniformity of the high-temperature gas between the buffer structure 2 and the cask 1. As a result, the heat removal performance of the buffer structure 2 can be further improved.

[0058] As described above, the buffer structure 2 is preferably provided with the third flow path 36 extending from the first flow path 34 or the second flow path 35 and penetrating the first buffer section 21. This can promote the release of high-temperature gas between the buffer structure 2 and the cask 1 to the outside, thereby further improving the heat removal performance of the buffer structure 2.

[0059] As described above, the first buffer section 21 and the second buffer section 22 preferably include a buffer material 31, an outer wall 32, and a heat insulating material 33. The outer wall 32 covers the outer surface of the buffer material 31. The heat insulating material 33 has a lower thermal conductivity than the outer wall 32 and is disposed between the outer wall 32 and the buffer material 31 at a position facing the cask 1. This makes it possible to suppress the transfer of heat from the high-temperature gas flowing between the buffer structure 2 and the cask 1 and radiant heat from the cask 1 to the buffer material 31. As a result, the thermal effects on the buffer material 31 and the like can be further reduced, thereby further suppressing the deterioration of the buffering performance of the buffer structure 2 due to the thermal effects.

[0060] It should be noted that the heat insulating material 33 does not necessarily have to be provided in both the first buffering section 21 and the second buffering section 22, but may be provided in at least one of the first buffering section 21 and the second buffering section 22. Even in this case, the thermal influence on the buffering material 31 and the like can be reduced, and therefore, the deterioration of the buffering performance of the buffer structure 2 due to the thermal influence can be suppressed.

[0061] As described above, the buffer structure 2 can reduce the thermal effects on the buffer material 31, etc., and therefore the structure of the buffer structure 2 is particularly suitable for cases where the buffer material 31 is made of hard foam resin or wood, which are relatively susceptible to thermal effects.

[0062] In the above-described buffer structure 2, for example, the number of the ribs 241 arranged in the circumferential direction may be increased in order to improve the fin efficiency of the ribs 241. In this case, by reducing the thickness of each rib 241 (i.e., the thickness in the circumferential direction), the total volume of the plurality of communicating flow paths 30 can be maintained relatively large.

[0063] The buffer structure 2 may further include plate-shaped fins protruding toward the cask 1 from at least one of the surface of the first buffer section 21 facing the cask end surface 11 (i.e., the lower surface) and the surface of the second buffer section 22 facing the cask side surface 12 (i.e., the inner surface). This can promote heat dissipation from the surface of the buffer structure 2. As a result, the heat removal performance of the buffer structure 2 can be further improved. The number of fins provided on the buffer structure 2 may be one or more.

[0064] 5, a plurality of fins 244 protruding from the inner surface of the second buffer section 22 toward the cask side surface 12 are arranged in the circumferential direction. Specifically, two fins 244 are arranged circumferentially spaced apart between the second rib sections 42 of each pair of circumferentially adjacent ribs 241. The radially inner ends of the plurality of fins 244 may be in contact with the cask side surface 12 or may be spaced radially outward from the cask side surface 12. When the plurality of fins 244 are in contact with the cask 1, heat dissipation from the surface of the cask 1 can also be promoted.

[0065] 5, multiple fins 245 protruding from the lower surface of the first buffer section 21 toward the cask end face 11 are arranged in the circumferential direction. Specifically, one fin 245 is disposed between the first rib portions 41 of each pair of circumferentially adjacent ribs 241, close to the central space 211. The lower ends of the multiple fins 245 may be in contact with the cask end face 11, or may be spaced upward from the cask end face 11. When the multiple fins 245 are in contact with the cask 1, heat dissipation from the surface of the cask 1 can also be promoted.

[0066] The number and arrangement of the fins 244, 245 provided in the buffer structure 2 may be changed in various ways. For example, the multiple fins 245 may be omitted, and only the fin 244 may be provided. Alternatively, the multiple fins 244 may be omitted, and only the fin 245 may be provided.

[0067] When the cask 1 is stored in an upright position (i.e., placed with the longitudinal direction approximately perpendicular to the direction of gravity), the above-described buffer structures 2 are attached to both longitudinal ends of the cask 1, as shown in FIG. 6. FIG. 6 is a vertical cross-sectional view of two buffer structures 2 attached to both ends of the cask 1. The buffer structure 2 on the left side in FIG. 6 shows a cross section including the rib 241. The buffer structure 2 on the right side in FIG. 6 is shifted in the circumferential direction from the buffer structure 2 on the left side, and shows a cross section including the communicating flow path 30.

[0068] In the buffer structure 2 attached to the cask 1 in the lying down position, high-temperature gas heated in the second flow passages 35 located on the lower side in the direction of gravity (i.e., the lower side in FIG. 6 ) among the plurality of second flow passages 35 arranged in the circumferential direction around the cask 1 passes through the communicating first flow passages 34 and flows out into the central space 211. Part of the high-temperature gas flows longitudinally within the central space 211 and is dissipated from the opening at the longitudinal end of the central space 211 (i.e., the end opposite the cask end face 11) into the space to the side of the buffer structure 2. Another part of the high-temperature gas that has flowed into the central space 211 passes through the plurality of first flow passages 34 and the plurality of second flow passages 35 located on the upper side in the direction of gravity (i.e., the upper side in FIG. 6 ) among the plurality of first flow passages 34 arranged in the circumferential direction, and is dissipated into the space above the buffer structure 2.

[0069] In this way, in the buffer structure 2 attached to the cask 1 in the lying down state, a high-temperature gas flow is formed that flows from the lower communicating flow path 30 in the direction of gravity to the upper communicating flow path 30 in the direction of gravity. This makes it possible to prevent high-temperature gas from accumulating between the cask 1 and the buffer structure 2, thereby improving the heat removal performance of the buffer structure 2. As a result, it is possible to prevent a decrease in the buffer performance of the buffer structure 2 due to thermal effects.

[0070] 6, the buffer structure 2 is provided with a third flow path 36 that extends upward along the direction of gravity from the second flow path 35 on the upper side in the direction of gravity and penetrates the second buffer part 22. This can promote the release of high-temperature gas between the buffer structure 2 and the cask 1 to the outside, and can further improve the heat removal performance of the buffer structure 2.

[0071] 7, the buffer structure 2 attached to the cask 1 in the lying-down state may be provided with a lid member 246 attached to the inside of the central space 211 (i.e., the through-hole in the radial center of the first buffer section 21) to close the central space 211. The lid member 246 faces the cask end surface 11 in the longitudinal direction at approximately the same longitudinal position as the surface of the first buffer section 21 facing the cask end surface 11. This allows the flow of high-temperature gas flowing from the lower communicating flow passage 30 in the direction of gravity to the upper communicating flow passage 30 in the direction of gravity to be rectified between the upper and lower communicating flow passages 30 (i.e., at a position corresponding to the central space 211). As a result, it is possible to promote the release of high-temperature gas between the buffer structure 2 and the cask 1 to the outside, and it is possible to further improve the heat removal performance of the buffer structure 2.

[0072] The above-mentioned cover member 246 is preferably detachably attached to the inside of the central space 211. This allows the cover member 246 to be removed when inspecting devices and the like provided on the cask end face 11, so that the inspection can be easily performed through the central space 211. Furthermore, the cover member 246 may be provided with holes or the like for passing cables or the like, as long as it can substantially close the central space 211.

[0073] Next, a buffer structure 2a according to a second embodiment of the present invention will be described. The buffer structure 2a is attached to both longitudinal ends of the cask 1 in a lying-down state (i.e., placed so that the longitudinal direction is horizontal). Fig. 8 is a front view of the buffer structure 2a attached to the cask 1, as seen from one longitudinal side. Fig. 9 is a side view showing a plurality of side ribs 247a provided on the right side of the buffer structure 2a shown in Fig. 8. In Fig. 9, the buffer main body 20 is shown in a vertical cross section including the central axis J1.

[0074] In the buffer structure 2a, the spacer 24a has, instead of the multiple ribs 241 (see FIG. 1) extending in the radial direction, multiple ribs 241a extending substantially parallel to the direction of gravity when attached to the cask 1. Other configurations of the buffer structure 2a are substantially the same as those of the above-described buffer structure 2, and in the following description, the same reference numerals as those of the corresponding configurations of the buffer structure 2 will be used for the components of the buffer structure 2a.

[0075] As shown in FIG. 8, the multiple ribs 241a are arranged horizontally and spaced apart from one another. Each rib 241a includes a first rib portion 41a and a second rib portion 42a. The first rib portion 41a is a substantially flat portion substantially perpendicular to the cask end surface 11 and extends substantially linearly in the direction of gravity between the first buffer portion 21 and the cask end surface 11. The first rib portion 41a is fixed to the first buffer portion 21, and the end of the first rib portion 41a opposite the first buffer portion 21 contacts the cask end surface 11. The width of the first rib portion 41a in the longitudinal direction is, for example, 30 mm to 70 mm. Above the central axis J1, the upper end of the first rib portion 41a is located at substantially the same radial position as the cask side surface 12. Below the central axis J1, the lower end of the first rib portion 41a is located at substantially the same radial position as the cask side surface 12.

[0076] The second rib portion 42a is a substantially flat portion that is substantially perpendicular to the cask side surface 12 (i.e., perpendicular to the tangent to the cask side surface 12 at the contact portion with the cask side surface 12) and extends substantially linearly along the longitudinal direction between the second buffer portion 22 and the cask side surface 12. The second rib portion 42a is fixed to the inner surface of the second buffer portion 22, and the radially inner end of the second rib portion 42a contacts the cask side surface 12. The second rib portion 42a on the lower side in the direction of gravity supports the weight of the cask 1. The height of the second rib portion 42a in the radial direction is, for example, 30 mm to 70 mm. The height of the second rib portion 42a in the radial direction is, for example, the same as the width of the first rib portion 41a in the longitudinal direction.

[0077] The second rib portion 42a extends from between the inner surface of the second buffer portion 22 and the cask side surface 12 to the outside in the longitudinal direction beyond the cask end surface 11, and one longitudinal end of the second rib portion 42a is continuous with the radially outer end of the first rib portion 41a. In other words, the rib 241a is a substantially L-shaped member. The other longitudinal end edge of the second rib portion 42a is located at substantially the same position as the longitudinal end edge of the second buffer portion 22. Note that the second rib portion 42a may protrude in the longitudinal direction from between the inner surface of the second buffer portion 22 and the cask side surface 12.

[0078] In the buffer structure 2a, among the plurality of ribs 241a, in each pair of horizontally adjacent ribs 241a, the gap between the first rib portions 41a of each pair of the ribs 241a forms a first flow path 34a through which gas can pass. Also, the gap between the second rib portions 42a of each pair of the ribs 241a forms a second flow path 35a through which gas can pass.

[0079] In the buffer structure 2a, a plurality of side ribs 247a are provided on both sides of the second buffer section 22 in the left-right direction in Fig. 8 (i.e., the direction perpendicular to the direction of gravity and the longitudinal direction). In the example shown in Figs. 8 and 9, five side ribs 247a are provided on each side of the second buffer section 22. The five side ribs 247a provided on the left side of the second buffer section 22 and the five side ribs 247a provided on the right side are approximately symmetrical with respect to an imaginary line that passes through the central axis J1 and extends in the direction of gravity in a front view.

[0080] The multiple side ribs 247a provided on each side of the second buffer section 22 are arranged at a distance from each other in the direction of gravity. Each side rib 247a is a substantially flat plate-shaped member fixed to the inner surface of the second buffer section 22 and protruding from the inner surface toward the cask side surface 12. The radially inner end of each side rib 247a contacts the cask side surface 12.

[0081] Each side rib 247a extends upward in the direction of gravity (i.e., the up-and-down direction in FIG. 9 ) from one side to the other in the longitudinal direction between the inner surface of the second buffer section 22 and the cask side surface 12. In the example shown in FIG. 9 , each side rib 247a extends obliquely upward in the longitudinal direction from the second buffer section 22 to the first buffer section 21. Contrary to the example shown in FIG. 9 , each side rib 247a may extend obliquely upward in the longitudinal direction from the first buffer section 21 to the second buffer section 22. The multiple side ribs 247a provided on each side of the second buffer section 22 are arranged approximately parallel to each other.

[0082] The gaps between the multiple side ribs 247a provided on each side of the second buffer 22 form side channels 37a that communicate with the space between the first buffer 21 and the cask end surface 11 at each side. In the example shown in Figure 9, high-temperature gas between each side of the second buffer 22 and the cask side surface 12 moves obliquely upward by the side channels 37a, is guided to the first channels 34a between the first buffer 21 and the cask end surface 11, and is dispersed into the space above the buffer structure 2a via the second channels 35a above the first channels 34a. Furthermore, if the multiple side ribs 247a are inclined in the opposite direction to that shown in Figure 9, the high-temperature gas between each side of the second buffer 22 and the cask side surface 12 moves obliquely upward by the side channels 37a in a direction away from the cask end surface 11 and is dispersed to the periphery of the buffer structure 2a from the end of the second buffer 22 opposite the first buffer 21.

[0083] As described above, in the buffer structure 2a that is mounted on the end of the cask 1 placed so that its longitudinal direction is horizontal (i.e., placed in a lying-down state), the spacer 24a preferably includes a plurality of ribs 241a arranged in the horizontal direction. Each of the plurality of ribs 241a includes a first rib portion 41a that extends in the direction of gravity between the first buffer portion 21 and the cask end surface 11, and a second rib portion 42a that extends in the longitudinal direction between the second buffer portion 22 and the cask side surface 12. The first rib portion 41a is a plate-shaped portion that is perpendicular to the cask end surface 11. The second rib portion 42a is a plate-shaped portion that is continuous with one end of the first rib portion 41a in the direction of gravity. Among the multiple ribs 241a, for each two horizontally adjacent ribs 241a, the gap between the first rib portions 41a of each two ribs 241a is the first flow path 34a, and the gap between the second rib portions 42a of each two ribs 241a is the second flow path 35a.

[0084] In this way, by dividing the space between the buffer structure 2a and the cask 1 into multiple communication channels 30a using the multiple plate-like ribs 241a, the volume of each communication channel 30a (i.e., the volume of each first channel 34a and each second channel 35a) can be increased. This increases the flow rate of high-temperature gas flowing between the buffer structure 2a and the cask 1, improving the heat removal performance of the buffer structure 2a. As a result, deterioration in the buffer performance of the buffer structure 2a due to thermal influences can be suppressed.

[0085] Furthermore, since the first rib portion 41a of each rib 241a extends in the direction of gravity, it is possible to prevent the first rib portion 41a from blocking the flow of high-temperature gas rising in the space between the first buffer portion 21 and the cask end surface 11. This makes it possible to increase the flow velocity of the high-temperature gas flowing between the buffer structure 2a and the cask 1, thereby further improving the heat removal performance of the buffer structure 2a.

[0086] As with the above-described rib 241, each of the ribs 241a preferably has a notch 242a on the side that contacts the cask 1, or a through-hole 243 (see FIG. 4) that penetrates through the thickness direction. This improves the temperature uniformity of the high-temperature gas between the buffer structure 2a and the cask 1 in the horizontal and / or circumferential directions. As a result, the heat removal performance of the buffer structure 2a can be further improved.

[0087] As described above, it is preferable that the buffer structure 2a further includes a plurality of side ribs 247a fixed to the second buffer 22 and in contact with the cask side surface 12 on each of both side portions of the second buffer 22 in the left-right direction (i.e., the direction perpendicular to the direction of gravity and the longitudinal direction). The plurality of side ribs 247a extend upward in the direction of gravity as they extend from one side to the other in the longitudinal direction between the second buffer 22 and the cask side surface 12. The gaps between the plurality of side ribs 247a form side flow paths 37a that communicate with the space between the first buffer 21 and the cask end surface 11.

[0088] In this way, by providing the side flow passages 37a facing diagonally upward on both the left and right sides of the cask 1, it is possible to prevent high-temperature gas from accumulating between the second buffer 22 and the cask side surface 12 and promote the dissipation of the high-temperature gas to the outside, thereby improving the heat removal performance of the buffer structure 2a.

[0089] In the buffer structure 2a, similarly to the buffer structure 2, it is preferable to provide a third flow path 36a that extends from the first flow path 34a or the second flow path 35a in the direction of gravity and penetrates the first buffer part 21 or the second buffer part 22. This can promote the release of high-temperature gas between the buffer structure 2a and the cask 1 to the outside, and can further improve the heat removal performance of the buffer structure 2a.

[0090] In the buffer structure 2a, the above-described lid member 246 (see FIG. 7) may be attached to the central space 211, similarly to the buffer structure 2. This rectifies the flow of rising high-temperature gas at a position corresponding to the central space 211, as described above, thereby further improving the heat removal performance of the buffer structure 2a. In addition, by removing the lid member 246, inspection of devices and the like provided on the cask end face 11 can be easily performed.

[0091] Next, a buffer structure 2b according to a third embodiment of the present invention will be described. The buffer structure 2b is attached to the end of the cask 1 in an upright or lying position. FIG. 10 is a plan view of the buffer structure 2b attached to the upper end of the cask 1 in an upright position. FIG. 11 is a longitudinal cross-sectional view of the buffer structure 2b taken along line XI-XI in FIG. 10. In the buffer structure 2b, the spacer 24b has a plurality of first protrusions 248b and a plurality of second protrusions 249b instead of the plurality of ribs 241 (see FIG. 1). The other configuration of the buffer structure 2b is substantially the same as that of the buffer structure 2 described above, and in the following description, the same reference numerals as those of the corresponding configuration of the buffer structure 2 will be used for the components of the buffer structure 2b.

[0092] The multiple first protrusions 248b are fixed to a surface of the first buffer 21 facing the cask end face 11 (hereinafter also referred to as the "first buffer inner surface 212"). The multiple first protrusions 248b are dispersed and spaced apart from one another across the entire first buffer inner surface 212. The multiple first protrusions 248b are arranged, for example, in a staggered pattern. The multiple first protrusions 248b protrude from the first buffer inner surface 212 toward the cask end face 11 and come into contact with the cask end face 11. Each first protrusion 248b is, for example, substantially flat with a main surface substantially perpendicular to the direction of gravity, and is fixed to the first buffer 21 by bolts or the like. Each first protrusion 248b preferably comes into surface contact with the cask end face 11. In the example shown in FIG. 10, the shape of each first protrusion 248b in a plan view is substantially circular, but this shape may be modified in various ways. Between the first buffer inner surface 212 of the buffer structure 2b and the cask end surface 11, the spaces between the multiple first protrusions 248b form first flow paths 34b.

[0093] The multiple second protrusions 249b are fixed to an inner surface of the second buffer 22 facing the cask side surface 12 (hereinafter also referred to as the "second buffer inner surface 222"). The multiple second protrusions 249b are dispersed and spaced apart from one another throughout the entire second buffer inner surface 222. The multiple second protrusions 249b are arranged, for example, in a staggered pattern. The multiple second protrusions 249b protrude from the second buffer inner surface 222 toward the cask side surface 12 and come into contact with the cask side surface 12. Each second protrusion 249b has, for example, a substantially plate shape that curves along the cask side surface 12 and is fixed to the second buffer 22 by bolts or the like. Each second protrusion 249b preferably comes into surface contact with the cask side surface 12. The shape of each second protrusion 249b in a side view is, for example, substantially circular, but this shape may be modified in various ways. The spaces between the second convex portions 249b form second flow paths 35b between the second buffer inner surface 222 of the buffer structure 2b and the cask side surface 12. The second flow paths 35b communicate with the first flow paths 34b outside the outer peripheral edge of the cask end surface 11.

[0094] When the buffer structure 2b is attached to the cask 1 in an upright position, the high-temperature gas between the second buffer section 22 and the cask side surface 12 rises through the second flow path 35b, flows radially inward through the first flow path 34b together with the high-temperature gas between the first buffer section 21 and the cask end surface 11, and is dissipated from the central space 211 to the space above the buffer structure 2b.

[0095] When the buffer structure 2b is attached to the cask 1 in the upright position, a portion of the high-temperature gas in the region of the second flow path 35b located on the lower side in the direction of gravity passes through the communicating first flow path 34b and the region of the second flow path 35b located on the upper side in the direction of gravity, and is dispersed into the space above the buffer structure 2b. Another portion of the high-temperature gas in the region of the second flow path 35b located on the lower side in the direction of gravity passes through the communicating first flow path 34b and flows into the central space 211. The portion of the high-temperature gas that flows into the central space 211 is dispersed into the space to the side of the buffer structure 2b from the opening at the longitudinal end of the central space 211. The other portion of the high-temperature gas that flows into the central space 211 passes through the region of the first flow path 34b located on the upper side in the direction of gravity and the region of the second flow path 35b located on the upper side in the direction of gravity, and is dispersed into the space above the buffer structure 2b.

[0096] As described above, in the buffer structure 2b, the spacer 24b includes a plurality of first protrusions 248b and a plurality of second protrusions 249b. The plurality of first protrusions 248b are spaced apart and distributed over the entire first buffer inner surface 212, which is the surface of the first buffer 21 facing the cask end surface 11, and protrude toward the cask end surface 11. The plurality of second protrusions 249b are spaced apart and distributed over the entire second buffer inner surface 222, which is the surface of the second buffer 22 facing the cask side surface 12, and protrude toward the cask side surface 12. The spaces between the plurality of first protrusions 248b are first flow paths 34b, and the spaces between the plurality of second protrusions 249b are second flow paths 35b.

[0097] This prevents high-temperature gas from accumulating between the cask 1 and the buffer structure 2b, improving the heat removal performance of the buffer structure 2b. As a result, it is possible to prevent a decrease in the buffer performance of the buffer structure 2b due to thermal influences. In addition, the impact load applied to the cask 1 when the cask 1 overturns, for example, can be dispersed by the multiple first convex portions 248b and / or the multiple second convex portions 249b, thereby reducing the impact load. The multiple first convex portions 248b and the multiple second convex portions 249b are formed of, for example, stainless steel.

[0098] In the buffer structure 2b, the region of the first buffer inner surface 212 that contacts the plurality of first protrusions 248b is defined as the first contact region, and the region of the second buffer inner surface 222 that contacts the plurality of second protrusions 249b is defined as the second contact region. The ratio of the total area of ​​the first contact region and the second contact region to the total area of ​​the first buffer inner surface 212 and the second buffer inner surface 222 is preferably 5% or more, and more preferably 25% or more. This allows the cask 1 to be favorably supported and the impact load when the cask 1 overturns, etc. to be favorably reduced. Furthermore, this ratio is preferably 60% or less, and more preferably 40% or less. This allows the volumes of the first flow path 34b and the second flow path 35b to be relatively large, favorably improving the heat removal performance of the buffer structure 2b.

[0099] In the buffer structure 2b, similarly to the buffer structure 2, it is preferable to provide a third flow path 36b that extends from the first flow path 34b or the second flow path 35b in the direction of gravity and penetrates the first buffer part 21 or the second buffer part 22. This can promote the release of high-temperature gas between the buffer structure 2b and the cask 1 to the outside, and can further improve the heat removal performance of the buffer structure 2b.

[0100] In the buffer structure 2b, the above-described lid member 246 (see FIG. 7) may be attached to the central space 211, similarly to the buffer structure 2. This rectifies the flow of rising high-temperature gas at a position corresponding to the central space 211, as described above, thereby further improving the heat removal performance of the buffer structure 2b. In addition, by removing the lid member 246, inspection of devices and the like provided on the cask end face 11 can be easily performed.

[0101] Next, a buffer structure 2c according to a fourth embodiment of the present invention will be described with reference to FIG. 12. FIG. 12 is a longitudinal cross-sectional view of the buffer structure 2c, corresponding to FIG. 2 described above. The buffer structure 2c is attached to the end of the cask 1c in an upright or lying position. In the example shown in FIG. 12, the buffer structure 2c is attached to the upper end of the cask 1c in an upright position. The cask 1c has a structure substantially similar to the above-described cask 1, except that the outer periphery of the cask end face 11c (i.e., the longitudinal end face) protrudes in the longitudinal direction beyond the radially inner portion of the outer periphery. In the following description, the outer periphery of the cask end face 11c (i.e., the approximately cylindrical portion protruding in the longitudinal direction) is also referred to as the "cask protrusion 13c."

[0102] In the buffer structure 2c, the outer periphery of the lower surface of the first buffer section 21c is recessed upward relative to the radially inner portion of the outer periphery to form a first buffer recess 213c. The lower surface of the first buffer recess 213c contacts the upper surface of the cask protrusion 13c over substantially the entire circumference. The shape of the contact area between the lower surface of the first buffer recess 213c and the upper surface of the cask protrusion 13c is a substantially annular surface. The lower surface of the first buffer section 21c faces the cask end surface 11c, spaced apart in the vertical direction, at a position radially inner than the cask protrusion 13c.

[0103] The buffer structure 2c includes a spacer 24c having a structure substantially similar to the rib 241 described above, except for the region of the buffer body 20 that contacts the cask protrusion 13c, and the spacer 24c includes multiple ribs 241c arranged substantially similarly to the rib 241. Furthermore, instead of the third flow path 36 shown in FIG. 2, the buffer structure 2c includes a third flow path 36c adjacent to the cask protrusion 13c on the radially inner side and a third flow path 36d adjacent to the cask protrusion 13c on the radially outer side. In this embodiment, the multiple third flow paths 36c and the multiple third flow paths 36d are arranged at substantially equal angular intervals in the circumferential direction around the central axis J1. Other configurations of the buffer structure 2c are substantially similar to those of the buffer structure 2 described above. In the following description, the components of the buffer structure 2c are denoted by the same reference numerals as the corresponding components of the buffer structure 2.

[0104] The rib 241c includes a first rib portion 41c and a second rib portion 42c. The first rib portion 41c is a substantially flat member substantially perpendicular to the cask end surface 11c. It is disposed radially inside the cask protrusion 13c and extends substantially linearly along the radial direction between the lower surface of the first buffer portion 21c and the cask end surface 11c. The first rib portion 41c is fixed to the lower surface of the first buffer portion 21c, and the lower end of the first rib portion 41c contacts the cask end surface 11c. In plan view, the radially inner end of the first rib portion 41c may or may not protrude radially inward from the inner surface of the first buffer portion 21c into the central space 211. The radially outer end of the first rib portion 41c contacts, for example, the inner surface of the cask protrusion 13c. A notch 242 is provided on the edge of the first rib portion 41c that contacts the cask 1c. Alternatively, instead of the notch 242, a through hole 243 (see FIG. 4) may be provided in the first rib portion 41c.

[0105] Similar to the second rib portion 42 described above, the second rib portion 42c is a substantially flat plate-shaped member substantially perpendicular to the cask side surface 12 and extends substantially linearly along the longitudinal direction between the inner surface of the second buffer portion 22 and the cask side surface 12. The second rib portion 42c is fixed to the inner surface of the second buffer portion 22, and the radially inner end of the second rib portion 42c contacts the cask side surface 12. The second rib portion 42c may or may not protrude downward from the lower end of the second buffer portion 22. The upper end of the second rib portion 42c contacts, for example, the lower surface of the first buffer recess 213c. The first rib portion 41c and the second rib portion 42c are not continuous. A notch 242 is provided in the second rib portion 42c on the side that contacts the cask 1c. Alternatively, a through-hole 243 (see FIG. 4) may be provided in the second rib portion 42c instead of the notch 242.

[0106] In the buffer structure 2c, multiple first rib portions 41c are arranged at approximately equal angular intervals in the circumferential direction. The space surrounded by each pair of circumferentially adjacent first rib portions 41c, the lower surface of the first buffer portion 21c, and the cask end surface 11c is the first flow path 34c through which gas can pass. The above-mentioned third flow path 36c extends approximately linearly upward from the upper end of the first flow path 34c along the gravity direction (i.e., the longitudinal direction) at the radially outer end of the first flow path 34c and penetrates the first buffer portion 21c. The cross-sectional shape of the third flow path 36c perpendicular to the longitudinal direction is, for example, approximately circular. The cross-sectional shape may be modified in various ways. Furthermore, the third flow path 36c does not necessarily have to extend along the gravity direction, but may extend obliquely upward from the first flow path 34c and penetrate the first buffer portion 21c. The third flow path 36c dissipates high-temperature gas in the first flow path 34c into the space above the buffer structure 2c. This promotes the release of high-temperature gas between the buffer structure 2c and the cask 1c to the outside, improving the heat removal performance of the buffer structure 2c.

[0107] In the buffer structure 2c, multiple second rib portions 42c are arranged at approximately equal angular intervals in the circumferential direction. The space surrounded by each pair of circumferentially adjacent second rib portions 42c, the inner surface of the second buffer portion 22, and the cask side surface 12 is a second flow path 35c through which gas can pass. The second flow path 35c is isolated from the first flow path 34c by the cask protrusion 13c and does not substantially communicate with the first flow path 34c.

[0108] The third flow passage 36d extends upward in a substantially linear manner from the upper end of the second flow passage 35c in the direction of gravity and penetrates the first buffer portion 21c. The cross-sectional shape of the third flow passage 36d perpendicular to the longitudinal direction is, for example, substantially circular. The cross-sectional shape may be modified in various ways. Furthermore, the third flow passage 36d does not necessarily have to extend in the direction of gravity. It may extend obliquely upward from the upper end of the second flow passage 35c and penetrate the first buffer portion 21c. Alternatively, the third flow passage 36d may extend obliquely upward or radially outward from the upper end of the second flow passage 35c and penetrate the second buffer portion 22. The third flow passage 36d dissipates high-temperature gas in the second flow passage 35c into the space surrounding the buffer structure 2c. This further improves the heat removal performance of the buffer structure 2c. The buffer structure 2c may be provided with only one of the third flow passage 36c and the third flow passage 36d.

[0109] 12, a portion of the lower surface of the first buffer section 21c of the buffer structure 2c contacts the cask end surface 11c over substantially the entire periphery, thereby isolating the first flow path 34c and the second flow path 35c, but instead of or in addition to this contact, a portion of the inner surface of the second buffer section 22 may contact the cask side surface 12 over the entire periphery, thereby isolating the first flow path 34c and the second flow path 35c. Also, in the buffer structure 2c, the first buffer recess 213c may not be provided, and the lower surface of the first buffer section 21c may be a substantially flat surface located at substantially the same position in the up-down direction over substantially the entire surface.

[0110] In the buffer structure 2c illustrated in FIG. 12, ribs 241c having substantially the same structure and arrangement as the ribs 241 are provided in the buffer body 20 except for the region that contacts the cask protrusion 13c, but this is not limiting. For example, ribs having substantially the same structure and arrangement as the ribs 241a of the spacer 24a may be provided in the buffer body 20 except for the region that contacts the cask protrusion 13c. In other words, the buffer structure 2a described above may be attached to the cask 1c. In this case, the ribs 241a are omitted in the region of the buffer body 20 of the buffer structure 2a that contacts the cask protrusion 13c. Alternatively, convex portions having substantially the same structure and arrangement as the first convex portion 248b and the second convex portion 249b of the spacer 24b may be provided in the buffer body 20 except for the region that contacts the cask protrusion 13c. In other words, the buffer structure 2b described above may be attached to the cask 1c. In this case, the spacer 24b is omitted from the region of the buffer body 20 of the buffer structure 2b that comes into contact with the cask protrusion 13c.

[0111] The buffer structure 2c may not require the above-described spacers. In this case, for example, the first flow path 34c and the second flow path 35c may be formed by contacting a plurality of ribs or protrusions provided on the cask end surface 11c and / or the cask side surface 12 with the buffer body 20 of the buffer structure 2c.

[0112] As described above, the buffer structure 2c includes a first buffer section 21c and a second buffer section 22. The first buffer section 21c faces the cask end face 11c, which is the longitudinal end face of the cask 1c, in the longitudinal direction. The first buffer section 21c extends radially outward from the outer circumferential edge of the cask end face 11c. The second buffer section 22 extends radially outward from the outer circumferential edge of the cask end face 11c, along the cask side face 12, which is the side face of the cask 1c, from the first buffer section 21c. The second buffer section 22 is a cylindrical section facing the cask side face 12 in the radial direction.

[0113] In the buffer structure 2c, a first flow path 34c through which gas can pass is formed between the first buffer section 21c and the cask end surface 11c. In addition, a second flow path 35c through which gas can pass is formed between the second buffer section 22 and the cask side surface 12. In the buffer structure 2c, a third flow path 36c or a third flow path 36d is provided, extending from the first flow path 34c or the second flow path 35c and penetrating the first buffer section 21c or the second buffer section 22.

[0114] As described above, this allows the high-temperature gas heated by the cask 1c to be dissipated from between the buffer structure 2c and the cask 1c to the outside via the third flow path 36c or the third flow path 36d, thereby improving the heat removal performance of the buffer structure 2c. This suppresses the temperature rise of the buffer structure 2c, thereby reducing the thermal impact on the buffer material 31 and the like. As a result, it is possible to suppress the deterioration of the buffer performance of the buffer structure 2c due to the thermal impact. Furthermore, it is possible to suppress the temperature rise of the cask 1c, thereby suppressing the deterioration of the gaskets and neutron shielding of the cask 1c. As a result, it is also possible to suppress the deterioration of the sealing performance and shielding performance of the cask 1c.

[0115] In the buffer structure 2c, the spacer 24c preferably includes a plurality of ribs 241c arranged radially in the circumferential direction, similar to the above-described spacer 24. Each of the plurality of ribs 241c includes a first rib portion 41c extending radially between the first buffer portion 21c and the cask end surface 11c, and a second rib portion 42c extending longitudinally between the second buffer portion 22 and the cask side surface 12. The first rib portion 41c is a plate-shaped portion perpendicular to the cask end surface 11. Of the plurality of first rib portions 41c, the gap between each two circumferentially adjacent first rib portions 41c is a first flow path 34c, and the gap between each two circumferentially adjacent second rib portions 42c is a second flow path 35c.

[0116] In this way, by dividing the space between the buffer structure 2c and the cask 1c into a plurality of first flow paths 34c and a plurality of second flow paths 35c using the plurality of plate-like ribs 241c, it is possible to increase the volume of each of the first flow paths 34c and each of the second flow paths 35c. As a result, it is possible to increase the flow rate of high-temperature gas flowing between the buffer structure 2c and the cask 1c, and further improve the heat removal performance of the buffer structure 2c.

[0117] As described above, each of the plurality of ribs 241c preferably has a notch 242 on the side that contacts the cask 1c, or a through-hole 243 (see FIG. 4) that penetrates in the thickness direction. This improves the temperature uniformity of the high-temperature gas between the buffer structure 2c and the cask 1c in the circumferential direction. As a result, the heat removal performance of the buffer structure 2c can be further improved.

[0118] In the buffer structure 2c, similar to the buffer structure 2, the first buffer section 21c and the second buffer section 22 preferably include a buffer material 31, an outer wall 32, and a heat insulating material 33. The outer wall 32 covers the outer surface of the buffer material 31. The heat insulating material 33 has a lower thermal conductivity than the outer wall 32 and is disposed between the outer wall 32 and the buffer material 31 at a position facing the cask 1c. This prevents the heat of the high-temperature gas flowing between the buffer structure 2c and the cask 1c and the radiant heat from the cask 1c from being transferred to the buffer material 31. As a result, the thermal effects on the buffer material 31 and the like can be further reduced, further preventing a decrease in the buffering performance of the buffer structure 2c due to the thermal effects.

[0119] When the cask 1c is stored in a lying-down state (i.e., placed with its longitudinal direction horizontal), the above-described buffer structures 2c are attached to both longitudinal ends of the cask 1c, as shown in FIG. 13. FIG. 13 is a vertical cross-sectional view of two buffer structures 2c attached to the respective ends of the cask 1c. The left-hand buffer structure 2c in FIG. 13 shows a cross-section including the rib 241c. The right-hand buffer structure 2c in FIG. 13 shows a cross-section shifted circumferentially from the left-hand buffer structure 2c, including the first flow path 34c and the second flow path 35c.

[0120] In the buffer structure 2c attached to the cask 1c in a lying-down position, among the multiple second flow passages 35c arranged circumferentially around the cask 1c, high-temperature gas heated in the second flow passages 35c located on the lower side in the direction of gravity (i.e., the lower side in FIG. 13 ) passes through the notches 242 of the second rib portion 42c and moves circumferentially to the second flow passages 35c located on the upper side in the direction of gravity. The high-temperature gas is dissipated from the second flow passages 35c located on the upper end of the buffer structure 2c to the outside via the third flow passage 36d and the end opening of the second flow passage 35c opposite the third flow passage 36d. Note that in the example shown in FIG. 13 , the third flow passage 36d may be omitted from the buffer structure 2c. In this case, the high-temperature gas in the second flow passages 35c located on the upper side in the direction of gravity is dissipated to the outside via the end opening of the second flow passage 35c opposite the first buffer portion 21c.

[0121] Furthermore, the high-temperature gas heated in the first flow passage 34c located on the lower side in the direction of gravity flows into the central space 211 through the opening at the radially inner end of the first flow passage 34c. A portion of the high-temperature gas flowing from the first flow passage 34c into the central space 211 is dissipated to the outside through the opening at the longitudinal end of the central space 211. Another portion of the high-temperature gas flows into the first flow passage 34c located on the upper side in the direction of gravity and is dissipated to the outside via the third flow passage 36c together with the high-temperature gas heated in the first flow passage 34c. This improves the heat removal performance of the buffer structure 2c. As a result, the deterioration of the buffer performance of the buffer structure 2c due to thermal effects can be suppressed.

[0122] The buffer structure 2c attached to the cask 1c in the lying-down state may be provided with a lid member 246 (see FIG. 7) attached to the inside of the central space 211 to close the central space 211. The lid member 246 faces the cask end surface 11c in the longitudinal direction at approximately the same longitudinal position as the surface of the first buffer 21c facing the cask end surface 11c. This allows the flow of high-temperature gas from the lower first flow passage 34c in the direction of gravity to the upper first flow passage 34c in the direction of gravity to be rectified between the upper and lower first flow passages 34c (i.e., at a position corresponding to the central space 211). As a result, it is possible to promote the release of high-temperature gas between the buffer structure 2c and the cask 1c to the outside, further improving the heat removal performance of the buffer structure 2c.

[0123] The above-mentioned lid member 246 is preferably detachably attached to the inside of the central space 211. This allows the lid member 246 to be removed when inspecting devices and the like provided on the cask end surface 11c, and the inspection can be easily performed through the central space 211. Furthermore, the lid member 246 may be provided with holes or the like for passing cables or the like, as long as it can substantially close the central space 211.

[0124] The above-described buffer structures 2, 2a, 2b, and 2c can be modified in various ways.

[0125] For example, in the buffer structure 2, the central space 211 may be omitted, and the first buffer portion 21 may be made substantially cylindrical. The same applies to the buffer structures 2a, 2b, and 2c.

[0126] In the buffer structure 2, the structure of the buffer body 20 is not necessarily limited to the above-described structure having the buffer material 31, the outer wall 32, and the heat insulating material 33, and may be modified in various ways. For example, the heat insulating material 33 may be omitted from the buffer body 20. The same applies to the buffer structures 2a, 2b, and 2c.

[0127] The above-mentioned notches 242 and through-holes 243 do not necessarily have to be provided in the rib 241 of the buffer structure 2. The same applies to the rib 241a of the buffer structure 2a and the rib 241c of the buffer structure 2c.

[0128] The first rib portion 41 does not necessarily have to be fixed to the first buffer portion 21, and does not necessarily have to be in contact with the first buffer portion 21. The second rib portion 42 does not necessarily have to be fixed to the second buffer portion 22, and does not necessarily have to be in contact with the second buffer portion 22. The rib 241 does not necessarily have to be fixed to the first buffer portion 21 and the second buffer portion 22, but is preferably fixed to the buffer main body 20. The rib 241 may be disposed between the buffer main body 20 and the cask 1 without being fixed to the buffer main body 20. The same applies to the first rib portions 41a, 41c, the second rib portions 42a, 42c, and the ribs 241a, 241c.

[0129] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory. [Explanation of symbols]

[0130] 1.1c cask 2,2a,2b,2c buffer structure 11,11c Cask end face 12 Cask side 20 Buffer body 21,21c 1st buffer section 22 Second buffer section 24, 24a, 24b, 24c spacers 31 Cushioning material 32 Exterior Wall 33 Insulation 34, 34a, 34b, 34c First flow path 35, 35a, 35b, 35c Second flow path 36, 36a, 36b, 36c, 36d Third flow path 37a Side channel 41, 41a, 41c First rib section 42, 42a, 42c Second rib section 211 Central space 212 Inner surface of the first buffer section 222 Inner surface of second buffer section 241, 241a, 241c Ribs 242 Notch 243 Through Hole 244,245 Finn 246 Lid member 247a Side rib 248b First convex part 249b Second convex part

Claims

1. A storage buffer structure that is attached to an end of a cylindrical cask that contains a fuel assembly during storage of the cask, a first buffer portion facing a cask end surface, which is an end surface of the cask in the longitudinal direction, while being spaced apart in the longitudinal direction, and extending radially outward beyond the outer circumferential edge of the cask end surface; a cylindrical second buffer section extending in a longitudinal direction from the first buffer section along a cask side surface that is a side surface of the cask, radially outward of the outer peripheral edge of the cask end surface, and facing the cask side surface while being spaced apart in the radial direction; a spacer disposed between the first buffer section and the end surface of the cask, forming a first flow path through which gas can pass between the first buffer section and the end surface of the cask, and disposed between the second buffer section and the side surface of the cask, forming a second flow path through which gas can pass, the second flow path communicating with the first flow path, between the second buffer section and the side surface of the cask; A storage buffer structure comprising:

2. 2. The storage cushioning structure of claim 1, the spacer includes a plurality of ribs arranged radially in a circumferential direction; Each of the plurality of ribs is a plate-shaped first rib portion extending along a radial direction between the first buffer portion and the cask end surface and perpendicular to the cask end surface; a plate-shaped second rib portion that is continuous with a radially outer end of the first rib portion and extends along the longitudinal direction between the second buffer portion and the side surface of the cask; Equipped with A storage buffer structure characterized in that, in each two circumferentially adjacent ribs among the plurality of ribs, the gap between the first rib portions of each of the two ribs is the first flow path, and the gap between the second rib portions of each of the two ribs is the second flow path.

3. 3. The storage cushioning structure according to claim 2, A storage buffer structure characterized in that each of the plurality of ribs has a through hole penetrating in the thickness direction, or a notch is provided on the edge that contacts the cask.

4. 2. The storage cushioning structure of claim 1, The cask is placed so that its longitudinal direction is horizontal, the spacer includes a plurality of ribs arranged in a horizontal direction; Each of the plurality of ribs is a plate-shaped first rib portion extending along the direction of gravity between the first buffer portion and the end surface of the cask and perpendicular to the end surface of the cask; a plate-like second rib portion that is continuous with one end of the first rib portion in the gravity direction and extends along the longitudinal direction between the second buffer portion and the side surface of the cask; Equipped with A storage buffer structure characterized in that, in each two horizontally adjacent ribs among the plurality of ribs, the gap between the first rib portions of each of the two ribs is the first flow path, and the gap between the second rib portions of each of the two ribs is the second flow path.

5. 5. The storage cushioning structure according to claim 4, the second buffer section further includes a plurality of side ribs at both left and right sides perpendicular to the direction of gravity and the longitudinal direction, the side ribs extending upward in the direction of gravity from one side to the other side in the longitudinal direction between the second buffer section and the cask side surface, and fixed to the second buffer section to come into contact with the cask side surface; A storage buffer structure, characterized in that the gaps between the plurality of side ribs are side flow paths that communicate with the space between the first buffer section and the end surface of the cask.

6. 5. The storage cushioning structure according to claim 4, A storage buffer structure characterized in that each of the plurality of ribs has a through hole penetrating in the thickness direction, or a notch is provided on the edge that contacts the cask.

7. 2. The storage cushioning structure of claim 1, A storage buffer structure characterized by further comprising a plate-shaped fin protruding toward the cask from at least one of the surfaces of the first buffer portion facing the end surface of the cask and the surface of the second buffer portion facing the side surface of the cask.

8. 2. The storage cushioning structure of claim 1, The spacer is a plurality of first protrusions that are spaced apart from one another and distributed over the entire inner surface of the first buffer, which is a surface of the first buffer facing the cask end surface, and that protrude toward the cask end surface; a plurality of second protrusions that are spaced apart from one another and distributed over the entire inner surface of the second buffer portion, which is a surface of the second buffer portion that faces the cask side surface, and that protrude toward the cask side surface; Equipped with A storage buffer structure, characterized in that the spaces between the plurality of first convex portions are the first flow paths, and the spaces between the plurality of second convex portions are the second flow paths.

9. 9. A storage cushioning structure according to any one of claims 1 to 8, A storage buffer structure, comprising: a third flow path extending from the first flow path or the second flow path and passing through the first buffer portion or the second buffer portion.

10. A storage buffer structure that is attached to an end of a cylindrical cask that contains a fuel assembly during storage of the cask, a first buffer portion that faces a cask end surface, which is an end surface of the cask in the longitudinal direction, in the longitudinal direction and extends radially outward beyond the outer circumferential edge of the cask end surface; a cylindrical second buffer portion extending in a longitudinal direction from the first buffer portion along a cask side surface that is a side surface of the cask, radially outward of the outer peripheral edge of the cask end surface, and facing the cask side surface in the radial direction; Equipped with a spacer is disposed between the first buffer section and the end surface of the cask, thereby forming a first flow path through which gas can pass between the first buffer section and the end surface of the cask; a spacer is disposed between the second buffer portion and the side surface of the cask, thereby forming a second flow path through which gas can pass between the second buffer portion and the side surface of the cask; A storage buffer structure, comprising: a third flow path extending from the first flow path or the second flow path and passing through the first buffer portion or the second buffer portion.

11. 11. The storage cushioning structure according to claim 1 or 10, At least one of the first buffer section and the second buffer section is Cushioning material, an outer wall covering the outer surface of the buffer material; a heat insulating material that is disposed between the outer wall and the buffer material at a position facing the cask and has a lower thermal conductivity than the outer wall; A storage buffer structure comprising:

12. 11. The storage cushioning structure according to claim 1 or 10, the first buffer portion is a cylindrical portion having a through hole in a radial center portion, The storage buffer structure is characterized in that it further comprises a lid member that is attached inside the through hole to block the through hole and that faces the end face of the cask in the longitudinal direction at the same position as the surface of the first buffer section that faces the end face of the cask.

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