Cask

Abstract

To provide a cask having a structure capable of preventing breakage of a buffer mounting bolt during horizontal falling.SOLUTION: A cask 100 comprises: a cylindrical container body 1 with a bottom that stores a radioactive substance; a lid 4 that closes an opening part of the container body 1; a buffer 5 that covers an outer periphery of the lid 4, where the buffer 5 has a buffer recess part F in which the lid 4 and a flange part 7 of the container body 1 are fitted; a plurality of buffer mounting bolts that fixes the buffer 5 to the flange part 7; and a plurality of lid mounting bolts 17 that fixes the lid 4 to the flange part 7. At outer peripheral corner parts of the lid 4, a space excluding the space for passing the shafts of the buffer mounting bolts and a space for storing the heads of the lid mounting bolts 17 is filled with a member.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a cask for storing radioactive material. [Background technology]

[0002] As described in Patent Documents 1 and 2, a cask is a container for storing radioactive materials (such as spent fuel), which includes, for example, a cylindrical cask body with a bottom, and three lids (a primary lid, a secondary lid, and a tertiary lid) that close the opening of the cask body. In addition, even if an accident (falling phenomenon) occurs during transportation of the cask, buffers for protecting the cask from impact are attached to the upper and lower parts of the outer periphery, respectively, so that the functions of the cask (heat removal function, sealing function, shielding function, and subcriticality maintenance function) are not impaired.

[0003] As can be seen from Fig. 2 of Patent Document 1 and Fig. 3 of Patent Document 2, conventionally, the upper surface of the outer peripheral corner of the tertiary lid is an annular surface (annular surface) that is continuous around the entire circumference and is one step lower than the upper surface of the lid so that the head of the tertiary lid mounting bolt does not protrude from the upper surface of the lid. The lower surface of the head of the tertiary lid mounting bolt abuts against this annular surface. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6633922 [Patent Document 2] Patent No. 6180123 Summary of the Invention [Problem to be solved by the invention]

[0005] It is assumed that the cask falls horizontally with its central axis in a horizontal position. During a horizontal fall, the outer surface of the buffer body attached to the upper part of the outer periphery of the cask (the buffer body covering the outer periphery of the tertiary lid) collides with the floor, and the inner surface of the buffer body collides with the cask body and the side of the tertiary lid.

[0006] In this case, in the case of a tertiary lid having the annular surface as described in Patent Documents 1 and 2, a space exists around the entire circumference of the cask between the outer corner of the tertiary lid and the inner surface of the buffer body facing the outer corner, so that a bending moment originating from the outer edge of the annular surface acts on the inner surface of the buffer body. This bending moment deforms the buffer body, and a shear force acts on the buffer body mounting bolts that fix the buffer body to the cask body. As a result, the buffer body mounting bolts may break.

[0007] An object of the present invention is to provide a cask having a structure capable of preventing breakage of the buffer mounting bolts when dropped horizontally. [Means for solving the problem]

[0008] The cask disclosed in the present application comprises a bottomed, cylindrical container body for storing radioactive material, a lid body for closing the opening of the container body, a buffer body covering the outer periphery of the lid body, the buffer body having a buffer body recess into which the lid body and the flange portion of the container body fit, a plurality of buffer body mounting bolts for fixing the buffer body to the flange portion, and a plurality of lid body mounting bolts for fixing the lid body to the flange portion, and at the outer periphery corners of the lid body, the space except for the space for passing the shaft portion of the buffer body mounting bolt and the space for accommodating the head of the lid body mounting bolt is filled with material. Effect of the Invention

[0009] According to the cask having the above configuration, it is possible to prevent the shock absorber mounting bolts from breaking when dropped horizontally. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a cross-sectional view of the top of a cask in accordance with one embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged view of part A shown in FIG. [Diagram 3] FIG. 3 is a cross-sectional view of a portion of a shock absorber mounting bolt, which corresponds to FIG. 2. [Figure 4] This is a view corresponding to Figure 2 and showing a cross section of a portion of the cask in the circumferential direction where there are no lid mounting bolts or buffer mounting bolts. [Diagram 5] This is a plan view of a portion (1 / 4 portion) of the tertiary lid. [Figure 6] 6 is a view corresponding to FIG. 5, showing a modified example of the tertiary lid shown in FIG. 5. [Figure 7] 1. FIG. 5 is a view corresponding to FIG. 4, showing a modified example of the cask shown in FIG. [Figure 8] 1. FIG. 5 is a view corresponding to FIG. 4, showing a modified example of the cask shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0012] The cask 100 is used to contain, transport, and store radioactive materials such as spent fuel, and as shown in Fig. 1, comprises a container body 1 that contains the radioactive materials, three lid bodies (2, 3, 4) that close the opening of the container body 1, and a buffer body 5. The three lid bodies are a primary lid 2, a secondary lid 3, and a tertiary lid 4.

[0013] Although the bottom is not shown in FIG. 1, the container body 1 has a bottomed cylindrical shape (a cylindrical shape with a bottom). The upper end of the container body 1, where an opening is provided, is a flange portion 7 to which three lid bodies (2, 3, 4) are attached. The flange portion 7 includes, in order from the lower side, a primary lid mounting portion 12, a secondary lid mounting portion 13, and a tertiary lid mounting portion 14. In addition, in order to suppress the emission of neutrons from inside the container body 1 to the outside, a side neutron shielding layer 6 is provided on the outer circumferential surface side of the container body 1. In addition, a plurality of trunnions (not shown) for handling are attached to the outer periphery of the container body 1. The material of the container body 1 is a metal (for example, carbon steel, alloy steel, or stainless steel) (the same is true for the three lid bodies (2, 3, 4)). The neutron shielding material constituting the side neutron shielding layer 6 is, for example, a resin such as epoxy resin or polyester resin, or a rubber such as silicone rubber or ethylene polypropylene rubber (the same applies to the cover neutron shielding layer 11 described later). In the following description, the direction parallel to the central axis of the container body 1 is defined as the axial direction X. The direction perpendicular to the central axis of the container body 1 (axis perpendicular direction) is defined as the radial direction Y.

[0014] The primary lid 2 is a lid body that seals the opening of the container body 1. The primary lid 2 is fixed to the primary lid mounting portion 12 of the flange portion 7 by a plurality of primary lid mounting bolts 15. A through hole 2a into which the shaft portion of the primary lid mounting bolt 15 is inserted is provided at the radial Y end portion (flange portion) of the primary lid 2. A seal member 8 is attached to the underside of the primary lid 2 slightly inside the through hole 2a. The seal member 8 is, for example, a metal gasket.

[0015] Further, the primary lid mounting portion 12 is provided with a female screw hole 12a into which the shaft of the primary lid mounting bolt 15 is screwed to fasten the primary lid mounting bolt 15.

[0016] The secondary lid 3 is disposed outside the primary lid 2 in the axial direction X, and is a lid body that maintains the pressure in the space S1 between it and the primary lid 2 together with the primary lid 2 and the vessel body 1. Like the primary lid 2, the secondary lid 3 is also a lid body that closes the opening of the vessel body 1. Inside the secondary lid 3, a lid neutron shielding layer 11 is provided.

[0017] The secondary lid 3 is fixed to the secondary lid mounting portion 13 of the flange portion 7 by a plurality of secondary lid mounting bolts 16. A through hole 3a into which the shaft portion of the secondary lid mounting bolt 16 is inserted is provided at the radial Y end portion (flange portion) of the secondary lid 3. A seal member 9 is attached to the underside of the secondary lid 3 slightly inside the through hole 3a. The seal member 9 is, for example, a metal gasket.

[0018] Further, the secondary lid mounting portion 13 is provided with a female screw hole 13a into which the shaft of the secondary lid mounting bolt 16 is screwed to fasten the secondary lid mounting bolt 16.

[0019] The tertiary lid 4 is a lid body installed outside the secondary lid 3 in the axial direction X. The tertiary lid 4 is a lid body that is attached when the cask 100 is transported, and is removed except in special cases when the cask 100 is in a storage state after the cask 100 is transported. The tertiary lid 4 is also a lid body that closes the opening of the container body 1, like the primary lid 2 and the secondary lid 3.

[0020] The tertiary lid 4 is fixed to the tertiary lid mounting portion 14 of the flange portion 7 by a plurality of tertiary lid mounting bolts 17 (lid body mounting bolts). A through hole 4a is provided at the radial Y end portion (flange portion) of the tertiary lid 4, into which a shaft portion 17a (see FIG. 2) of the tertiary lid mounting bolt 17 is inserted. A seal member 10 is attached to the underside of the tertiary lid 4 slightly inside the through hole 4a. The seal member 10 is, for example, a rubber O-ring.

[0021] In addition, a countersunk hole 4d for accommodating the head 17b of the tertiary lid mounting bolt 17 is provided on the outer circumferential corner E of the tertiary lid 4 above the through hole 4a and concentric with the through hole 4a. As shown in FIG. 5, this countersunk hole 4d is provided independently for each tertiary lid mounting bolt 17. The diameter of the countersunk hole 4d is larger than the diameter of the through hole 4a. The depth of the countersunk hole 4d is set to be equal to or greater than the height of the head 17b of the tertiary lid mounting bolt 17. The countersunk hole 4d is provided in the tertiary lid 4, and the head 17b of the tertiary lid mounting bolt 17 is accommodated in the countersunk hole 4d, so that the head 17b of the tertiary lid mounting bolt 17 does not protrude from the top surface of the tertiary lid 4. The countersunk hole 4d forms a space for accommodating the head 17b of the tertiary lid mounting bolt 17.

[0022] The tertiary lid mounting part 14 is provided with a female screw hole 14a into which the tertiary lid mounting bolt 17 is fastened by screwing in the shaft part 17a of the tertiary lid mounting bolt 17. As shown by the reference numerals in FIG. 2 and the like, in a portion where the tertiary lid 4 and the tertiary lid mounting part 14 are fitted in the axial direction X, a convex part 4b is formed on the tertiary lid 4, and a step part 14b (concave part) that fits with the convex part 4b is formed on the tertiary lid mounting part 14. This configuration prevents the tertiary lid 4 from shifting laterally (shifting in the radial direction Y) relative to the container body 1. Note that, contrary to this configuration, a convex part may be formed on the tertiary lid mounting part 14, and a concave part that fits with the convex part in the axial direction X may be formed on the tertiary lid 4.

[0023] In this embodiment, the convex portion 4b is an annular convex portion that continues around the entire circumference of the cask 100. The stepped portion 14b is an annular recessed portion that continues around the entire circumference of the cask 100.

[0024] The buffer 5 is attached when the cask 100 is transported, and serves to protect the cask 100 from impact in the unlikely event that the cask 100 falls. The buffer 5 is attached to the upper part (head) of the vessel body 1. In other words, the buffer 5 is an upper buffer. Although not shown in the figure, a similar buffer (lower buffer) is also attached to the lower part (bottom) of the vessel body 1.

[0025] The buffer 5 is composed of an annular main shock absorber 18, a columnar auxiliary shock absorber 19, and a cover plate 20. The cover plate 20 is a plate that covers the main shock absorber 18 and the auxiliary shock absorber 19. The cover plate 20 is composed of an outer cover plate 22 and an inner cover plate 23. The main shock absorber 18 has a predetermined thickness in the axial direction X and the radial direction Y, and has an appropriate shock transmission area in each direction. The material of the main shock absorber 18 and the auxiliary shock absorber 19 is, for example, wood, foamed resin such as urethane foam, or foamed metal such as aluminum foam. The material of the cover plate 20 is metal (for example, carbon steel or stainless steel). By covering the main shock absorber 18 and the auxiliary shock absorber 19 with the cover plate 20, it is possible to prevent the shock absorbers 18 and 19 from being crushed and scattered when colliding with the floor surface. The buffer 5 covers the outer periphery of the tertiary lid 4. The buffer 5 has a buffer recess F into which the tertiary lid 4 and the flange portion 7 of the container body 1 fit.

[0026] As shown in Fig. 3, the buffer 5 is fixed to the tertiary lid mounting portion 14 of the flange portion 7 by a plurality of buffer mounting bolts 21. A through hole 4c (through hole for buffer mounting bolt) into which the shaft portion 21a of the buffer mounting bolt 21 is inserted is provided at the radial direction Y end portion (flange portion) of the tertiary lid 4. The through hole 4c forms a space through which the shaft portion 21a of the buffer mounting bolt 21 passes. The through hole 4c is provided independently for each buffer mounting bolt 21 at an outer circumferential corner portion E of the tertiary lid 4.

[0027] The tertiary lid mounting portion 14 is provided with a female screw hole 14c into which the shaft portion 21a of the buffer mounting bolt 21 is screwed to fasten the buffer mounting bolt 21.

[0028] Further, the main shock absorber 18 constituting the buffer 5 is provided with a first through hole 18a extending in the axial direction X. The inner cover plate 23 is provided with a second through hole 23a that is concentric with the first through hole 18a and has a smaller diameter than the first through hole 18a. The shaft 21a of the buffer mounting bolt 21 is passed through the second through hole 23a. The head 21b of the buffer mounting bolt 21 housed in the first through hole 18a is pressed against the upper surface of the inner cover plate 23.

[0029] FIG. 5 is a plan view of a part (1 / 4 part) of the tertiary lid 4. FIG. 5 shows a plurality of through holes 4a into which the shaft portion 17a of the tertiary lid mounting bolt 17 is inserted, a countersunk hole 4d for accommodating the head portion 17b, and a plurality of through holes 4c into which the shaft portion 21a of the buffer mounting bolt 21 is inserted. As can be seen from FIG. 5, the plurality of through holes 4a, the countersunk hole 4d, and the plurality of through holes 4c are provided on the same circumference at the radial Y end of the tertiary lid 4. That is, the plurality of tertiary lid mounting bolts 17 and the plurality of buffer mounting bolts 21 are arranged on the same circumference. FIG. 2, which shows a cross section of the tertiary lid mounting bolt 17 portion, corresponds to the BB cross section in FIG. 5, which shows only the tertiary lid 4. FIG. 3, which shows a cross section of the buffer mounting bolt 21 portion, corresponds to the CC cross section in FIG. 5. 4 is a diagram showing a cross section of a portion where tertiary cover mounting bolts 17 and buffer body mounting bolts 21 are not present, and corresponds to the cross section taken along line DD in FIG.

[0030] In the cask 100 of this embodiment, as shown in Fig. 2 and Fig. 5, the space for accommodating the head 17b of the tertiary lid mounting bolt 17 is formed by the countersunk hole 4d provided independently for each tertiary lid mounting bolt 17, and as shown in Fig. 3 and Fig. 5, the space for passing the shaft portion 21a of the buffer mounting bolt 21 is formed by the through hole 4c provided independently for each buffer mounting bolt 21. As a result, at the outer peripheral corner portion E of the tertiary lid 4, the periphery of the countersunk hole 4d and the through hole 4c (see Fig. 2, Fig. 3, Fig. 5), between the countersunk hole 4d and the through hole 4c adjacent in the circumferential direction (see Fig. 5), and between the countersunk holes 4d adjacent in the circumferential direction (see Fig. 4, Fig. 5) are solid structures. That is, the space other than the space for passing the shaft portion 21a of the buffer mounting bolt 21 and the space for accommodating the head 17b of the tertiary lid mounting bolt 17 is filled with the steel material (member) constituting the tertiary lid 4.

[0031] Here, it is assumed that the cask 100 falls horizontally with its central axis horizontal. During the horizontal fall, the outer surface (outer cover plate 22) of the buffer body 5 collides with the floor surface, and the flange portion 7 and the side surface of the tertiary lid 4 collide with the inner surface (inner cover plate 23).

[0032] At this time, in the cask 100 of this embodiment, as described above, the space at the outer circumferential corner E of the tertiary lid 4, except for the space through which the shaft portion 21a of the buffer mounting bolt 21 passes and the space for accommodating the head portion 17b of the tertiary lid mounting bolt 17, is filled with the steel material (member) constituting the tertiary lid 4 (solid structure). As a result, the shock load is easily transmitted in the direction perpendicular to the axis from the buffer 5 (main shock absorber 18) to the tertiary lid 4. Therefore, in the cask 100 of this embodiment, when the cask 100 collides with the floor during horizontal drop, a bending moment (bending moment M shown by the two-dot chain line in Figs. 2 to 4) acting on the inner cover plate 23 of the buffer 5 is unlikely to occur, as in the case of a cask equipped with a tertiary lid (a tertiary lid having a space at the outer circumferential corner around the entire circumference of the cask) described in Patent Documents 1 and 2. Since bending moment M is unlikely to occur, bending deformation is unlikely to occur in the inner cover plate 23, and as a result, shear force is unlikely to act on the buffer mounting bolt 21 that fixes the buffer 5 to the container body 1, preventing the buffer mounting bolt 21 from breaking.

[0033] In this embodiment, the countersunk holes 4d and through holes 4c are machined in the tertiary lid 4, so that the space at the outer circumferential corner E of the tertiary lid 4 is solid, except for the space through which the shaft 21a of the buffer mounting bolt 21 passes and the space for accommodating the head 17b of the tertiary lid mounting bolt 17. This makes it easy to realize a solid structure that prevents the buffer mounting bolt 21 from breaking. In other words, this embodiment is excellent in terms of ease of manufacturing the cask.

[0034] In the cask 100 of this embodiment, a convex portion 4b is formed on the tertiary lid 4 at a portion where the tertiary lid 4 and the flange portion 7 fit together in the axial direction X, and a step portion 14b (concave portion) that fits with the convex portion 4b is formed on the tertiary lid mounting portion 14. As described above, a convex portion may be formed on the tertiary lid mounting portion 14, and a concave portion that fits with the convex portion in the axial direction X may be formed on the tertiary lid 4.

[0035] According to this configuration, when the cask 100 falls horizontally, the load of the tertiary lid 4 (load acting in the radial direction Y) can be supported by the flange portion 7, so that shear forces are less likely to act on the buffer mounting bolts 21 and the tertiary lid mounting bolts 17, thereby preventing their breakage.

[0036] Here, it is desirable that the maximum radial gap S1 between the shaft portion 21a of the buffer mounting bolt 21 and the through hole 4c into which the shaft portion 21a is inserted is larger than the maximum radial gap S2 between the convex portion 4b and the step portion 14b (concave portion).

[0037] The maximum radial Y gap S1 refers to the radial Y gap between the shaft portion 21a and the through hole 4c when the shaft portion 21a of the buffer mounting bolt 21 abuts against the inner surface of the through hole 4c, in other words, when the axis of the shaft portion 21a is most displaced in the radial Y from the center of the through hole 4c.

[0038] 3 shows a case where the axis of the buffer mounting bolt 21 coincides with the center of the through hole 4c. When the radial Y gap between the shaft portion 21a and the through hole 4c at this time is S1a, the radial Y maximum gap S1 = S1a x 2. Similarly, FIG. 3 shows a case where the axis of the tertiary lid 4 coincides with the axis of the container body 1. When the radial Y gap between the convex portion 4b and the step portion 14b (concave portion) at this time is S2a, the radial Y maximum gap S2 = S2a x 2.

[0039] If the radial Y maximum gap S1 is made larger than the radial Y maximum gap S2, even if the tertiary lid 4 shifts when the cask 100 collides with the floor surface when it is dropped horizontally and the radial Y gap between the convex portion 4b on the floor collision side and the step portion 14b (concave portion) disappears, a gap remains between the shaft portion 21a of the buffer mounting bolt 21 and the through hole 4c. This makes it possible to prevent the shaft portion 21a of the buffer mounting bolt 21 from colliding with the inner surface of the through hole 4c, and as a result, it is possible to prevent the buffer mounting bolt 21 from breaking due to a shear force.

[0040] In addition, it is desirable that the maximum radial Y gap S3 between the head 21b of the buffer mounting bolt 21 and the first through hole 18a provided in the buffer 5, and the maximum radial Y gap S4 between the shaft portion 21a of the buffer mounting bolt 21 and the second through hole 23a provided in the buffer 5 (inner cover plate 23) are all larger than the maximum radial Y gap S5 between the outer peripheral surface of the flange portion 7 and the inner surface of the buffer recess F, and the maximum radial Y gap S6 between the outer peripheral surface of the tertiary cover 4 and the inner surface of the buffer recess F.

[0041] The maximum radial Y gap S3 is the radial Y gap between the head 21b of the buffer mounting bolt 21 and the first through hole 18a when the head 21b abuts against the inner surface of the first through hole 18a, in other words, when the axis of the head 21b is most displaced in the radial Y from the center of the first through hole 18a.

[0042] 3 shows a case where the axis of the shock absorber mounting bolt 21 coincides with the center of the first through hole 18a. When the radial Y gap between the head 21b and the first through hole 18a at this time is S3a, the radial Y maximum gap S3 = S3a x 2. Similarly, FIG. 3 shows a case where the axis of the shock absorber mounting bolt 21 coincides with the center of the second through hole 23a. When the radial Y gap between the shaft 21a and the second through hole 23a at this time is S4a, the radial Y maximum gap S4 = S4a x 2.

[0043] FIG. 3 shows a case where the axis of the container body 1 (flange portion 7) coincides with the axis of the buffer 5 (buffer recess F). When the radial Y gap between the outer circumferential surface of the flange portion 7 and the inner surface of the buffer recess F is S5a, the radial Y maximum gap S5=S5a×2. Similarly, FIG. 3 shows a case where the axis of the tertiary lid 4 coincides with the axis of the buffer 5 (buffer recess F). When the radial Y gap between the outer circumferential surface of the tertiary lid 4 and the inner surface of the buffer recess F is S6a, the radial Y maximum gap S6=S6a×2. Note that, in FIG. 3, the outer circumferential surface of the tertiary lid 4 and the outer circumferential surface of the flange portion 7 are flush with each other, but the outer diameter of the tertiary lid 4 and the outer diameter of the flange portion 7 may be slightly different in size.

[0044] The radial Y gap between the outer circumferential surface of the flange portion 7 and the inner surface of the buffer recess F, and the radial Y gap between the outer circumferential surface of the tertiary lid 4 and the inner surface of the buffer recess F are designed taking into consideration manufacturing tolerances and workability. These radial Y gaps are easily crushed (eliminated) when the cask 100 collides with the floor when dropped horizontally.

[0045] If both the radial Y maximum gap S3 and the radial Y maximum gap S4 are larger than the radial Y maximum gap S5 and the radial Y maximum gap S6, gaps are likely to remain between the head 21b of the buffer mounting bolt 21 and the first through hole 18a, and between the shaft 21a of the buffer mounting bolt 21 and the second through hole 23a when the cask 100 collides with the floor surface when it is dropped horizontally. This makes it possible to prevent the head 21b of the buffer mounting bolt 21 from colliding with the inner surface of the first through hole 18a, and the shaft 21a of the buffer mounting bolt 21 from colliding with the inner surface of the second through hole 23a, and as a result, it is possible to prevent the buffer mounting bolt 21 from breaking due to a shear force.

[0046] FIG. 6 is a view corresponding to FIG. 5, showing a modified example of the tertiary lid 4 shown in FIG.

[0047] The difference between the tertiary lid 4 shown in Fig. 5 and the tertiary lid 4 shown in Fig. 6 is the shape of the countersunk hole 4d for accommodating the head 17b of the tertiary lid mounting bolt 17. The countersunk hole 4d shown in Fig. 5 is circular in plan view. In contrast, the countersunk hole 4d shown in Fig. 6 is U-shaped in plan view. The countersunk hole 4d shown in Fig. 6 opens on the side surface of the tertiary lid 4.

[0048] In the case of the circular countersunk hole 4d shown in Fig. 5, depending on the cask, only a small gap may be provided between the countersunk hole 4d and the side surface of the tertiary lid 4 in a plan view. In such a case, the thickness between the countersunk hole 4d and the side surface of the tertiary lid 4 becomes very thin. In such a case, the countersunk hole 4d is made U-shaped as shown in Fig. 6.

[0049] Even in the case of a U-shaped countersunk hole 4d as shown in Fig. 6, the space for accommodating the head 17b of the tertiary lid mounting bolt 17 is formed by the countersunk hole 4d provided independently for each tertiary lid mounting bolt 17. Therefore, at the outer peripheral corner E of the tertiary lid 4, most of the space between adjacent countersunk holes 4d in the circumferential direction becomes a solid structure. Therefore, similar to the case of the circular countersunk hole 4d shown in Fig. 5, when the cask 100 falls horizontally and hits the floor, the shock load is easily transmitted in the axis-perpendicular direction from the buffer 5 (main shock absorber 18) to the tertiary lid 4.

[0050] FIG. 7 is a view corresponding to FIG. 4, showing a modification of the cask 100 shown in FIG.

[0051] The cask 101 shown in Figure 7 differs from the cask 100 shown in Figure 1 in the material that fills the space at the outer corner E of the tertiary lid 4, except for the space for passing the shaft portion 21a of the buffer mounting bolt 21 and the space for accommodating the head portion 17b of the tertiary lid mounting bolt 17.

[0052] In the cask 100 shown in Fig. 1, the above-mentioned excluding space is filled (solid structure) by the steel material constituting the tertiary lid 4, in other words, by a portion of the tertiary lid 4. In contrast, in the cask 101 shown in Fig. 7, the above-mentioned excluding space is filled (solid structure) by a portion of the buffer body 5.

[0053] Specifically, a part of the corner of the buffer recess F in the buffer 5 is formed into a convex shape (convex portion 24) that protrudes toward the outer circumferential corner E of the tertiary lid 4, so that the space at the outer circumferential corner E of the tertiary lid 4, except for the space through which the shaft portion 21a of the buffer mounting bolt 21 passes and the space that houses the head portion 17b of the tertiary lid mounting bolt 17, is filled with a part of the buffer 5 (solid structure). The convex portion 24 is composed of the main shock absorber 18 and an inner cover plate 23 that covers it. A plurality of convex portions 24 are provided. Each convex portion 24 is formed into an arc shape in a plan view.

[0054] With the above structure, as in the case of the cask 100 shown in Fig. 1, the shock load is easily transmitted in the direction perpendicular to the axis from the buffer 5 (main shock absorber 18) to the tertiary lid 4. Therefore, when the cask collides with the floor during a horizontal drop, a bending moment acting on the inner cover plate 23 of the buffer 5 is unlikely to occur, as in the case of a cask equipped with a tertiary lid (a tertiary lid with spaces at the outer corners around the entire circumference of the cask) described in Patent Documents 1 and 2. Since the bending moment M is unlikely to occur, bending deformation is unlikely to occur in the inner cover plate 23, and as a result, a shear force is unlikely to act on the buffer mounting bolts 21 that fix the buffer 5 to the vessel body 1, and breakage of the bolts can be prevented.

[0055] The upper surface of the radial end portion (flange portion) of the tertiary lid 4 is an annular surface (annular surface) that is continuous around the entire circumference and is one step lower than the lid upper surface.

[0056] FIG. 8 is a view corresponding to FIG. 4, showing a further modification of the cask 100 shown in FIG.

[0057] The cask 102 shown in Figure 8 is the same as the modified example shown in Figure 7, but differs from the cask 100 shown in Figure 1 in the material that fills the space at the outer corner E of the tertiary lid 4, except for the space for passing the shaft portion 21a of the buffer mounting bolt 21 and the space for accommodating the head portion 17b of the tertiary lid mounting bolt 17.

[0058] In the cask 100 shown in Fig. 1, as a result of machining the tertiary lid 4 with the countersunk hole 4d and the like, the above-mentioned remaining space is filled (solid structure) with a portion of the tertiary lid 4. In contrast, in the cask 102 shown in Fig. 8, the above-mentioned remaining space is filled (solid structure) with a block member 25 that is attached to the tertiary lid 4 later.

[0059] There are a plurality of block members 25, each of which has an arc shape in a plan view. The space except for the space through which the shaft portion 21a of the buffer mounting bolt 21 passes and the space for accommodating the head portion 17b of the tertiary lid mounting bolt 17 is filled with the plurality of arc-shaped block members 25. The block members 25 are attached to the tertiary lid 4 by, for example, welding. The material of the block members 25 is metal (for example, carbon steel, alloy steel, or stainless steel).

[0060] Incidentally, the upper surface of the radial Y end portion (flange portion) of the tertiary lid 4 before the block member 25 is attached is an annular surface (annular surface) that is continuous around its entire circumference and is one step lower than the lid upper surface.

[0061] The present invention is not limited to the above-described embodiments, and it is possible to combine elements of the above-described embodiments as appropriate and to make various modifications to the above-described embodiments without departing from the spirit of the present invention.

[0062] For example, the above embodiment can be modified as follows.

[0063] The casks 100, 101, and 102 in the above embodiments are all used to contain, transport, and store radioactive materials, and include a primary lid 2, a secondary lid 3, and a tertiary lid 4. On the other hand, in the case of a cask dedicated to transportation, a cask that includes only the primary lid 2, i.e., only one lid body, may be used.

[0064] In this case, the buffer 5 is located on the upper surface of the primary lid 2, and the primary lid 2 and the flange portion 7 of the container body 1 are fitted into the buffer recess F. Therefore, in the case of the primary lid 2, the space at the outer circumferential corner of the lid, excluding the space through which the shaft portion 21a of the buffer mounting bolt 21 passes and the space for accommodating the head of the lid mounting bolt, is filled with a member. In other words, the present invention may be applied to a cask having only one lid, rather than a cask having multiple lids. [Explanation of symbols]

[0065] 1: Container body 4: Tertiary lid (lid body) 4b: Convex part 4c: Through hole (for the shock absorber mounting bolt) 4d: Counterbore 5:Buffer 7: Flange part 14b: Step portion (recess) 17: Tertiary lid mounting bolt (lid body mounting bolt) 17b:Head 18a: 1st through hole 21: Shock absorber mounting bolt 21a: Shaft part 21b:Head 23a: 2nd through hole 24: Convex part (convex shape) 100, 101, 102: Cask E: Outer periphery corner F: Cushion recess X: Axial direction Y: Radial direction

Claims

1. A cylindrical container body with a bottom for storing radioactive material; A lid that closes the opening of the container body; a buffer body covering an outer periphery of the lid body, the buffer body having a buffer body recess into which the lid body and a flange portion of the container body are fitted; A plurality of shock absorber mounting bolts that fix the shock absorber to the flange portion; A plurality of lid mounting bolts for fixing the lid to the flange portion; Equipped with the space for accommodating the head of the lid body mounting bolt is formed by a countersunk hole provided in the outer circumferential corner of the lid independently for each lid body mounting bolt, and the space for passing the shank of the buffer body mounting bolt is formed by a buffer body mounting bolt through hole provided in the outer circumferential corner independently for each buffer body mounting bolt, so that at the outer circumferential corner, the space except for the space for passing the shank of the buffer body mounting bolt and the space for accommodating the head of the lid body mounting bolt is filled with a member, a maximum radial gap between a head of the buffer mounting bolt and a first through hole provided in the buffer that accommodates the head of the buffer mounting bolt, and a maximum radial gap between a shaft portion of the buffer mounting bolt and a second through hole provided in the buffer through which the shaft portion of the buffer mounting bolt passes, are all larger than a maximum radial gap between an outer peripheral surface of the flange portion and an inner side surface of the buffer recess, and a maximum radial gap between an outer peripheral surface of the cover body and the inner side surface. Cask.

2. A cylindrical container body with a bottom for storing radioactive material; A lid that closes the opening of the container body; a buffer body covering an outer periphery of the lid body, the buffer body having a buffer body recess into which the lid body and a flange portion of the container body are fitted; A plurality of shock absorber mounting bolts that fix the shock absorber to the flange portion; A plurality of lid mounting bolts for fixing the lid to the flange portion; Equipped with A part of the corner of the buffer recess is formed into a convex shape that protrudes toward the outer circumferential corner of the lid, so that the space at the outer circumferential corner, except for a space for passing the shaft of the buffer mounting bolt and a space for accommodating the head of the lid mounting bolt, is filled with a member. Cask.

3. A cylindrical container body with a bottom for storing radioactive material; A lid that closes the opening of the container body; a buffer body covering an outer periphery of the lid body, the buffer body having a buffer body recess into which the lid body and a flange portion of the container body are fitted; A plurality of shock absorber mounting bolts that fix the shock absorber to the flange portion; A plurality of lid mounting bolts for fixing the lid to the flange portion; Equipped with the space for accommodating the head of the lid body mounting bolt is formed by a countersunk hole provided in the outer circumferential corner of the lid independently for each lid body mounting bolt, and the space for passing the shank of the buffer body mounting bolt is formed by a buffer body mounting bolt through hole provided in the outer circumferential corner independently for each buffer body mounting bolt, so that at the outer circumferential corner, the space other than the space for passing the shank of the buffer body mounting bolt and the space for accommodating the head of the lid body mounting bolt is filled with a member, a protrusion is formed on one of the cover body and the flange portion at a portion where the cover body and the flange portion are fitted together in the axial direction, and a recess that fits with the protrusion is formed on the other of the cover body and the flange portion, a maximum radial gap between a shaft portion of the shock absorber mounting bolt and the shock absorber mounting bolt through hole is larger than a maximum radial gap between the convex portion and the concave portion; Cask.

4. A cylindrical container body with a bottom for storing radioactive material; A lid that closes the opening of the container body; a buffer body covering an outer periphery of the lid body, the buffer body having a buffer body recess into which the lid body and a flange portion of the container body are fitted; A plurality of shock absorber mounting bolts that fix the shock absorber to the flange portion; A plurality of lid mounting bolts for fixing the lid to the flange portion; Equipped with At the outer circumferential corner of the lid, a space other than a space for passing a shaft portion of the buffer body mounting bolt and a space for accommodating a head portion of the lid body mounting bolt is filled with a member, a maximum radial gap between a head of the buffer mounting bolt and a first through hole provided in the buffer that accommodates the head of the buffer mounting bolt, and a maximum radial gap between a shaft portion of the buffer mounting bolt and a second through hole provided in the buffer through which the shaft portion of the buffer mounting bolt passes, are all larger than a maximum radial gap between an outer peripheral surface of the flange portion and an inner side surface of the buffer recess, and a maximum radial gap between an outer peripheral surface of the cover body and the inner side surface. Cask.

5. The cask according to claim 2 or 3, a maximum radial gap between a head of the buffer mounting bolt and a first through hole provided in the buffer that accommodates the head of the buffer mounting bolt, and a maximum radial gap between a shaft portion of the buffer mounting bolt and a second through hole provided in the buffer through which the shaft portion of the buffer mounting bolt passes, are all larger than a maximum radial gap between an outer peripheral surface of the flange portion and an inner side surface of the buffer recess, and a maximum radial gap between an outer peripheral surface of the cover body and the inner side surface. Cask.

6. In the cask according to any one of claims 1, 2, 4 and 5, At a portion where the lid body and the flange portion are fitted together in the axial direction, a convex portion is formed on one of the lid body and the flange portion, and a concave portion that fits with the convex portion is formed on the other of the lid body and the flange portion. Cask.

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