Shock absorbing structure

Abstract

To enhance shock absorbing capacity while securing strength of a support structure in a shock absorbing structure.SOLUTION: The shock absorbing structure 2 is attached to an end portion 11 of a cylindrical cask 1 that houses a fuel assembly. A first annular plate 31 extending radially inward and outward from an end portion of the cylindrical member 33 on the side of the cask 1, a second annular plate 32 extending radially inward from a position of the cylindrical member 33 away from the first annular plate 31, a plurality of reinforcing members 35 connecting an inner peripheral surface of the cylindrical member 33, the first annular plate 31, and the second annular plate 32 and arranged in a circumferential direction, and a shock-absorbing part 4 including a shock-absorbing material and extending radially outward from an outer peripheral surface of the cylindrical member 33 to the outside of the outer peripheral edge of the cask 1. 111 J1.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a cushioning structure. [Background technology]

[0002] Conventionally, casks are used to house spent fuel assemblies (hereinafter simply referred to as "fuel assemblies") removed from nuclear reactors. A cask is a cylindrical container in which the fuel assemblies are transported or stored. During transport or storage of the cask, buffer structures (buffers) are attached to both ends of the cask to absorb or reduce the impact on the cask body in the unlikely event of a fall or other accident.

[0003] For example, the buffer body of Patent Document 1 is composed of an end surface side member, a peripheral surface side member, and a shock absorber. The end surface side member has two plates that are arranged along the end surface of the cask and face each other with a gap between them, and multiple end surface reinforcing members that connect the two plates. The peripheral surface side member has a cylindrical body joined to the two plates. When the end surface side member is attached to the end surface of the cask, the peripheral surface side member covers the outer peripheral surface of the end of the cask. The shock absorber is disposed outside the outer peripheral surface of the cylindrical body. In addition, in the buffer body for a cask of Patent Document 2, wooden shock absorbing blocks are combined in a ring shape to form the shock absorber, and the shock absorbing blocks are provided with spaces for adjusting the shock absorption characteristics. The buffer structure of Patent Document 3 has a first section formed of a porous material and a second section formed of a porous material having a density different from that of the first section and vertically overlapping the first section. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4681681 [Patent Document 2] Patent No. 4523980 [Patent Document 3] Patent Publication No. 2021-4831 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, in the buffer structure (buffer) of Patent Document 1, a buffer section (shock absorber) is arranged on the outside of the outer peripheral surface of a cylindrical body, and two plates and multiple end reinforcing members are arranged inside the cylindrical body. In this buffer structure, the cylindrical body, two plates, and multiple end reinforcing members can be considered to form a support structure that supports the buffer section from the inside. Meanwhile, in the buffer structure, by increasing the size of the buffer section, it is possible to easily reduce the impact on the cask in the event of a drop accident, etc., but in reality, there are limitations on the external size of the buffer structure. In the buffer structure of Patent Document 1, the cylindrical body is arranged along the outer peripheral surface of the end of the cask, so the width of the buffer section that can be arranged outside the cylindrical body in the radial direction is small, making it difficult to improve the shock absorption capacity.

[0006] The present invention has been made in consideration of the above-mentioned problems, and has as its object to increase the shock absorbing capacity of a cushioning structure while ensuring the strength of the support structure. [Means for solving the problem]

[0007] A first aspect of the present invention is a buffer structure attached to the end of a cylindrical cask that contains a fuel assembly, and when the buffer structure is attached to the cask, the buffer structure comprises a cylindrical member that is centered on the central axis of the cask and faces one end face of the cask radially inward from the outer peripheral edge of the cask, a first annular plate that extends radially inward and outward from the cask-side end of the cylindrical member, a second annular plate that extends radially inward from a position on the cylindrical member away from the first annular plate, a plurality of reinforcing members that connect the inner peripheral surface of the cylindrical member, the first annular plate, and the second annular plate and are arranged circumferentially, and a buffer section that includes buffer material and extends radially from the outer peripheral surface of the cylindrical member to outside the outer peripheral edge of the cask.

[0008] A second aspect of the present invention is a cushioning structure of the first aspect, wherein the cushioning portion comprises a first cushioning block formed from a porous material and arranged on the outer surface side of the cylindrical member, and a second cushioning block arranged outside the first cushioning block in the radial direction and formed from a porous material having a density different from that of the first cushioning block.

[0009] A third aspect of the present invention is the cushioning structure of the second aspect, wherein the density of the first cushioning block is higher than the density of the second cushioning block.

[0010] A fourth aspect of the present invention is the cushioning structure of the first aspect (which may be any one of the first to third aspects), in which no other reinforcing members are provided inside the plurality of reinforcing members in the radial direction.

[0011] A fifth aspect of the present invention is the buffer structure of any one of the first to fourth aspects, further comprising a perforated plate covering the opening of the second annular plate. [Effects of the Invention]

[0012] According to the present invention, it is possible to increase the impact absorption capacity while ensuring the strength of the support structure formed by the cylindrical member, the first annular plate, the second annular plate, and the plurality of reinforcing members. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. [Figure 2] FIG. 2 is a vertical cross-sectional view showing the cushioning structure. [Figure 3] FIG. [Figure 4] FIG. 10 is a perspective view showing a support structure of a comparative example. [Figure 5] 10A and 10B are diagrams illustrating other examples of the cushioning structure. DETAILED DESCRIPTION OF THE INVENTION

[0014] Fig. 1 is a plan view showing a buffer structure 2 according to one embodiment of the present invention. Fig. 2 is a longitudinal cross-sectional view of the 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.

[0015] The cask 1 is a substantially cylindrical container centered on a central axis J1 extending in the vertical direction in Fig. 2, and contains a fuel assembly (i.e., a spent fuel assembly). The cask 1 has a shielding function for shielding against radiation, a sealing function for sealing in radioactive materials, a subcriticality maintaining function for maintaining the fuel assembly in a subcritical state, and a heat removal function for dissipating heat from the fuel assembly.

[0016] The buffer structures 2 are attached to both end portions 11 of the cask 1 in the direction of the central axis J1. The two buffer structures 2 provided at both end portions 11 are symmetrical with respect to a plane perpendicular to the central axis J1. The buffer structures 2 absorb or reduce impacts on the cask body in the event of a fall or other accident during transportation or storage of the cask 1. Hereinafter, the state in which the buffer structures 2 are attached to the cask 1 will be referred to as the "attached state," and the explanation will focus on one of the buffer structures 2 in the attached state, but the other buffer structure 2 also has a similar structure. Furthermore, for convenience of explanation, the up and down are defined in accordance with Figure 2, but the up and down direction is not limited to the vertical direction.

[0017] As shown in FIGS. 1 and 2, the buffer structure 2 includes a support structure 3, a buffer section 4, and a cover plate 51. The cover plate 51 is a disk-shaped member centered on a central axis J1 and made of metal such as steel. The cover plate 51 directly faces the center of the end face 111 at the end 11 of the cask 1 (hereinafter also referred to as the "cask end 11"). The cover plate 51 is attached to a second annular plate 32 of the support structure 3, which will be described later.

[0018] FIG. 3 is a perspective view showing the support structure 3, illustrating the buffer structure 2 without the buffer section 4 and cover plate 51. The support structure 3 is a main plate (support) or skeletal structure that supports the buffer section 4, and is directly fixed to the cask 1. As shown in FIGS. 1 to 3, the support structure 3 includes a first annular plate 31, a second annular plate 32, a first cylindrical member 33, a second cylindrical member 34, a plurality of first reinforcing members 35, a plurality of second reinforcing members 36, and an auxiliary annular plate 37. These components are formed of, for example, a metal such as steel.

[0019] The first annular plate 31 is an annular plate member centered on the central axis J1 and directly faces the outer edge of the end face 111 of the cask end 11. For example, the first annular plate 31 is in approximate contact with the end face 111 of the cask end 11. In this specification, "approximately in contact" between two members means that the two members are in contact with or close to each other (for example, close to each other within 100 mm). The outer diameter (radius) of the first annular plate 31 is approximately the same as the outer diameter of the cask end 11. The inner diameter of the first annular plate 31 is not particularly limited, but is, for example, 1 / 3 or more and 2 / 3 or less of the outer diameter of the first annular plate 31. As shown in FIGS. 1 and 3 , the buffer section 4 and the first annular plate 31 are provided with a plurality of through holes 49, 39 arranged in the circumferential direction (the circumferential direction centered on the central axis J1). The support structure 3 is fixed to the cask end 11 by bolts inserted into each through hole 49, 39.

[0020] 2, the second annular plate 32 is disposed slightly above the first annular plate 31 and is substantially parallel to the first annular plate 31. The first annular plate 31 and the second annular plate 32 face each other in the direction of the central axis J1. The outer diameter of the second annular plate 32 is smaller than the outer diameter of the cask end portion 11 and the outer diameter of the first annular plate 31. The inner diameter of the second annular plate 32 is, for example, equal to or larger than the inner diameter of the first annular plate 31 (less than the outer diameter of the first annular plate 31).

[0021] The first cylindrical member 33 has a cylindrical shape centered on the central axis J1, and the outer diameter of the first cylindrical member 33 is smaller than the outer diameter of the cask end portion 11. The lower end of the first cylindrical member 33 is fixed to the upper surface of the first annular plate 31 by welding or the like, and faces the end surface 111 of the cask end portion 11 via the first annular plate 31. In other words, the first annular plate 31 extends radially inward and outward (radially around the central axis J1) from the end of the first cylindrical member 33 facing the cask end portion 11 over its entire circumference. The upper end of the first cylindrical member 33 is fixed to the outer peripheral edge of the second annular plate 32 by welding or the like. That is, the second annular plate 32 extends radially inward over its entire circumference from the upper end of the first cylindrical member 33. The first cylindrical member 33 may protrude above the second annular plate 32, as long as the second annular plate 32 is connected to the first cylindrical member 33 at a position spaced apart from the first annular plate 31.

[0022] Each of the multiple first reinforcing members 35 is a so-called rib, and has a plate shape that is approximately parallel to the radial direction and the direction of the central axis J1. Each first reinforcing member 35 is disposed in a space surrounded by the inner circumferential surface of the first cylindrical member 33, the upper surface of the first annular plate 31, and the lower surface of the second annular plate 32, and is fixed to these surfaces by welding or the like. That is, the first reinforcing member 35 connects the inner circumferential surface of the first cylindrical member 33, the first annular plate 31, and the second annular plate 32. Typically, the multiple first reinforcing members 35 are arranged at equal angular intervals in the circumferential direction (at 30° intervals in the examples of FIGS. 1 and 3). The first reinforcing members 35 may be shaped like a block or the like, other than a plate.

[0023] As shown in Fig. 3, when the cover plate 51 is omitted, none of the components constituting the buffer structure 2 are arranged radially inside the first annular plate 31, the plurality of first reinforcing members 35, and the second annular plate 32. Therefore, the end face 111 of the cask end portion 11 is exposed. In practice, as shown in Figs. 1 and 2, the outer peripheral edge of the cover plate 51 is fixed to the inner peripheral edge of the second annular plate 32 by welding or the like, and the cover plate 51 closes the opening of the second annular plate 32 (i.e., the area inside the inner peripheral edge). This prevents workers from coming into contact with the end face 111 of the cask end portion 11, which is at high temperature.

[0024] The second cylindrical member 34 is cylindrical and centered on the central axis J1, and is arranged around the outer circumferential surface of the cask end 11. The upper end of the second cylindrical member 34 is fixed to the outer circumferential edge of the first annular plate 31 by welding or the like. The second cylindrical member 34 is a member that hangs down from the outer circumferential edge of the first annular plate 31 around its entire circumference. The auxiliary annular plate 37 is an annular plate member that is centered on the central axis J1, and surrounds the outer circumferential surface of the cask end 11. The inner circumferential edge of the auxiliary annular plate 37 is fixed to the lower end of the second cylindrical member 34 by welding or the like. The auxiliary annular plate 37 protrudes radially outward from the lower end of the second cylindrical member 34 around its entire circumference.

[0025] Each of the multiple second reinforcing members 36 is a so-called rib, and has a plate shape that is approximately parallel to the radial direction and the direction of the central axis J1. Each second reinforcing member 36 is fixed to the outer circumferential surface of the second cylindrical member 34 and the upper surface of the auxiliary annular plate 37 by welding or the like. The multiple second reinforcing members 36 are arranged at equal angular intervals in the circumferential direction (at 30° intervals in the example of FIG. 3). The second reinforcing members 36 may be in a shape other than a plate, such as a block.

[0026] As shown in FIGS. 1 and 2, the buffer unit 4 has a generally annular shape centered on the central axis J1 and includes a cover unit 46, a first buffer block 41, a second buffer block 42, and a third buffer block 43. The cover unit 46 is formed of a metal such as stainless steel (SUS), and is indicated by a thick line in FIG. 2. The cover unit 46 includes a first portion 461, a second portion 462, a third portion 463, and a fourth portion 464. The first portion 461 is generally cylindrical and extends upward from the upper end of the first cylindrical member 33. The second portion 462 is generally annular and extends radially outward from the upper end of the first portion 461. The third portion 463 is generally cylindrical and extends downward from the outer circumferential edge of the second portion 462. The fourth portion 464 has a substantially annular plate shape, and extends radially inward from the lower end of the third portion 463 to connect to the outer periphery of the auxiliary annular plate 37. In the buffer structure 2, the cover portion 46, and the first cylindrical member 33, first annular plate 31, second cylindrical member 34, and auxiliary annular plate 37 of the support structure 3 form an annular storage space R centered on the central axis J1. Depending on the design of the buffer portion 4, a portion of the cover portion 46 may also be provided at a position facing the support structure 3, and the storage space R may be formed by the cover portion 46 alone.

[0027] Each of the first buffer block 41, the second buffer block 42, and the third buffer block 43 is made of a molded buffer material and has an annular shape centered on the central axis J1. The buffer material is made of a porous material, and a preferred example is a hard foamed resin such as hard polyurethane foam. The buffer material may also be made of other porous materials (for example, foamed metal or wood). In this embodiment, the same porous material is used for the first to third buffer blocks 41 to 43, but different porous materials may also be used.

[0028] The first to third buffer blocks 41-43 are arranged in the storage space R. Preferably, the storage space R is densely filled with buffer material. In one example, each of the buffer blocks 41-43 is made up of a plurality of divided members divided at equal angular intervals in the circumferential direction. In other words, the buffer blocks 41-43 are an assembly of a plurality of divided members. The buffer blocks 41-43 may also be formed from a single annular member. Depending on the design of the buffer section 4, each of the buffer blocks 41-43 may be divided in the radial direction.

[0029] In the storage space R, the first cushioning material block 41 is disposed on the outer peripheral surface side of the first cylindrical member 33. In the example of FIG. 2, the first cushioning material block 41 is in substantial contact with the outer peripheral surface of the first cylindrical member 33 and the upper surface of the first annular plate 31. The second cushioning material block 42 is disposed radially outward of the first cushioning material block 41 and is directly sandwiched between the first cushioning material block 41 and the third portion 463 of the cover portion 46. The second cushioning material block 42 also covers the upper part of the first cushioning material block 41. The third cushioning material block 43 is in substantial contact with the auxiliary annular plate 37 and the fourth portion 464 of the cover portion 46. In the example of FIG. 2, on the fourth portion 464 side of the storage space R, the entire space between the second cylindrical member 34 and the third portion 463 is filled with the third cushioning material block 43.

[0030] The densities (bulk densities) of the first to third buffer material blocks 41 to 43 are different from one another. The density of the first buffer material block 41 is higher than the density of the second buffer material block 42 and lower than the density of the third buffer material block 43. In this embodiment, in which the same porous material is used, the porosity of the first buffer material block 41 is lower than the porosity of the second buffer material block 42 and higher than the porosity of the third buffer material block 43. In the first to third buffer material blocks 41 to 43 in FIG. 2, the higher the density, the narrower the spacing between the hatched lines.

[0031] Here, a support structure in a buffer structure of a comparative example will be described. Fig. 4 is a perspective view showing a support structure 9 of the comparative example. In the support structure 9 of the comparative example, compared to the support structure 3 of Fig. 3, the second annular plate 32 and the first reinforcing member 35 are omitted, and the first annular plate 31 is changed to a disk-shaped support plate 91. In addition, an auxiliary cylindrical member 92 is provided in the center of the support plate 91, and a plurality of reinforcing plates 94 are attached, extending radially from the outer circumferential surface of the auxiliary cylindrical member 92 and connecting to a cylindrical member 93 (a cylindrical main plate corresponding to the first cylindrical member 33).

[0032] In the support structure 9 of the comparative example, multiple reinforcing plates 94 are provided to prevent the cylindrical member 93, which is in radial contact with the buffer portion, from deforming into an elliptical shape when a cask equipped with a buffer structure including the support structure 9 is dropped horizontally (dropped with the central axis J1 oriented substantially horizontally). However, when an actual drop test using a 1 / 3-scale model was conducted, the cylindrical member 93 of the comparative example did not deform into an elliptical shape, but instead deformed radially inward between adjacent reinforcing plates 94. This may affect the control of the degree of collapse of the buffer portion, potentially preventing the desired (i.e., designed) shock absorption capacity from being achieved. Note that even when the cask is dropped vertically (dropped with the central axis J1 oriented substantially vertically), the cylindrical member 93 may be pushed radially inward by the crushed buffer material and deformed.

[0033] In contrast, the buffer structure 2 described above, when attached to the cask 1, includes a first annular plate 31 extending radially inward and outward from the end of the first cylindrical member 33 facing the cask 1, a second annular plate 32 extending radially inward from a position on the first cylindrical member 33 away from the first annular plate 31, and a plurality of first reinforcing members 35 arranged circumferentially and connecting the inner circumferential surface of the first cylindrical member 33, the first annular plate 31, and the second annular plate 32. In the buffer structure 2, the first cylindrical member 33 is reinforced over the entire circumference by the second annular plate 32 (in other words, the cylindrical main plate has a three-dimensional structure), thereby improving the strength (and rigidity) of the support structure 3. As a result, in the event of a drop of the cask 1 or other accident, radial inward deformation of the first cylindrical member 33 is prevented or suppressed, and the buffer structure 2 can more reliably exhibit the desired shock absorption capacity. In fact, when a dynamic analysis (dynamic structural analysis) was performed on the above-mentioned buffer structure 2, it was confirmed that the deformation behavior of the first cylindrical member (cylindrical main plate) was significantly smaller than that of the buffer structure having the comparative support structure 9, and that the amount of crushing of the buffer section approached the expected value.

[0034] Furthermore, in the above-described buffer structure 2, the strength of the support structure 3 can be ensured without providing the disk-shaped support plate 91 and auxiliary cylindrical member 92 as in the support structure 9 of the comparative example. In other words, it is possible to improve the strength of the support structure 3 only by using a small space near the inside of the first cylindrical member 33, without providing other reinforcing members radially inside the plurality of first reinforcing members 35. As a result, the weight of the buffer structure 2 can be reduced. Note that, depending on the design of the buffer structure 2, other reinforcing members may be provided inside the plurality of first reinforcing members 35.

[0035] As mentioned above, there is a limit to the external size of the buffer structure. Therefore, when a cylindrical member that contacts the inside of the buffer section in the radial direction is provided along the outer circumferential surface of the cask end, as in Japanese Patent No. 4681681 (the above-mentioned Patent Document 1), the width of the buffer section that can be arranged outside the cylindrical member becomes small, making it difficult to improve the shock absorption capacity.

[0036] Meanwhile, in the above-mentioned buffer structure 2 in the installed state, the first cylindrical member 33 faces one end surface 111 of the cask 1 radially inside the outer circumferential edge of the cask 1. Also, the buffer section 4 including the buffer material extends radially from the outer circumferential surface of the first cylindrical member 33 (i.e., from inside the outer circumferential edge of the cask 1) to outside the outer circumferential edge of the cask 1. This increases the radial width of the buffer section 4, i.e., increases the crushing stroke of the buffer material, and easily improves the shock absorption capacity of the buffer structure 2.

[0037] Preferably, the buffer section 4 includes a first buffer block 41 and a second buffer block 42. The first buffer block 41 is formed of a porous material and is disposed on the outer peripheral surface side of the first cylindrical member 33. The second buffer block 42 is disposed radially outward of the first buffer block 41 and is formed of a porous material having a different density from that of the first buffer block 41. By using the first buffer block 41 and the second buffer block 42 having different densities in this manner, a design with improved shock absorption capacity can be easily achieved. Furthermore, in the buffer structure 2, the radial width of the buffer section 4 can be increased, making it easy to arrange the first buffer block 41 and the second buffer block 42.

[0038] Preferably, the density of the first buffer block 41 is higher than the density of the second buffer block 42. The buffer material of the buffer section 4 in this embodiment has heat shrinkability, and the density of the inner first buffer block 41, which is more susceptible to the heat of the cask 1, is higher than the density of the outer second buffer block 42, thereby preventing deformation of the buffer material due to the heat of the cask 1.

[0039] Fig. 5 is a diagram showing another example of the buffer structure 2, and is a vertical cross-sectional view corresponding to Fig. 2. The buffer structure 2 of Fig. 5 differs from the buffer structure 2 of Fig. 2 in that a cover plate 51a having a plurality of holes 511 (hereinafter referred to as a "perforated plate 51a" to distinguish it from the cover plate 51 of Fig. 2) is provided. The other configuration is the same as in Fig. 2, and the same components are denoted by the same reference numerals.

[0040] The perforated plate 51a is, for example, a punched metal or a mesh plate, and has a large number of holes 511 uniformly formed therein. The outer peripheral edge of the perforated plate 51a is fixed to the second annular plate 32 by welding or the like, and the opening of the second annular plate 32 is covered by the perforated plate 51a. As a result, the space surrounded by the first cylindrical member 33 in the radial direction communicates with the space above the perforated plate 51a through the multiple holes 511. The buffer structure 2 in FIG. 5 can efficiently dissipate heat from the end surface 111 of the cask end 11 and prevent workers from coming into contact with the high-temperature end surface 111.

[0041] The buffer structure 2 can be modified in various ways.

[0042] Depending on the design of the buffer section 4, the density of the first buffer block 41 may be equal to or less than the density of the second buffer block 42. Furthermore, the density of the buffer material may be constant throughout the entire buffer section 4.

[0043] In cases where the amount of heat generated in the cask 1 is small, the cover plates 51, 51a may be omitted.

[0044] 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]

[0045] 1 cask 2 Buffer structure 3 Support structure 4 Buffer section 31 First annular plate 32 Second annular plate 33 First cylindrical member 35 First reinforcing member 41 First buffer block 42 Second buffer block 51a Perforated plate 111 (Cask) End J1 center axis

Claims

1. A buffer structure attached to an end of a cylindrical cask that accommodates a fuel assembly, a cylindrical member that is cylindrical about the central axis of the cask when the buffer structure is attached to the cask and faces one end surface of the cask radially inward of the outer circumferential edge of the cask; a first annular plate extending radially inward and outward from the cask-side end of the cylindrical member; a second annular plate extending radially inward from a position in the cylindrical member away from the first annular plate; a plurality of reinforcing members that connect an inner circumferential surface of the cylindrical member, the first annular plate, and the second annular plate and are arranged in a circumferential direction; a buffer portion including a buffer material and extending from the outer peripheral surface of the cylindrical member to a position outside the outer peripheral edge of the cask in the radial direction; A buffer structure comprising:

2. 2. The cushioning structure according to claim 1, The buffer section is a first buffer block formed of a porous material and disposed on the outer peripheral surface side of the cylindrical member; a second buffer block disposed outside the first buffer block in the radial direction and formed of a porous material having a density different from that of the first buffer block; A buffer structure comprising:

3. The cushioning structure according to claim 2, A cushioning structure in which the density of the first cushioning block is higher than the density of the second cushioning block.

4. 2. The cushioning structure according to claim 1, A buffer structure in which no other reinforcing members are provided inside the plurality of reinforcing members in the radial direction.

5. 5. The cushioning structure according to claim 1, The buffer structure further includes a perforated plate covering the opening of the second annular plate.

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