JP2023059088A - Basket of used fuel transportation cask or storage cask - Google Patents

Abstract

To provide a basket of a used fuel transportation cask or a storage cask which can avoid the buckling of a neutron absorption plate material at a vertical fall of the fuel transportation cask or the storage cask.SOLUTION: A basket of a used fuel transportation cask or a storage cask has a basket main body 2 which is accommodated in the used fuel transportation cask or the storage cask. The basket main body 2 is formed by laminating lattice members formed into lattice shapes in a plurality of pieces in an axial direction B of the used fuel transportation cask or the storage cask by a combination of the plate-shaped members in a plurality of pieces. At least a part of the plate-shaped members is constituted by superimposing a stiff plate material 11 being a stiff member, and a neutron absorption plate material 12 having neutron absorption performance, and larger than the stiff plate material 11 in a linear expansion coefficient. In the axial direction B, a dimension of the neutron absorption plate material 12 is smaller than a dimension of the stiff plate material 11. In an entire use temperature range of the basket main body 2, the stiff plate materials 11 which adjoin each other in the axial direction B abut on each other, and a clearance a is formed between the neutron absorption plate materials 12 which adjoin each other in the axial direction B.SELECTED DRAWING: Figure 5

Description

The present invention relates to baskets contained in spent fuel transportation or storage casks.

In Patent Literature 1, a rigid plate material that serves as a strength member and a neutron absorbing plate material that serves as a neutron absorber are laminated in the lateral direction to form a basket that is stored in a spent fuel transportation or storage cask (cask). is configured. By varying the neutron absorption performance of the neutron absorption plate material in the vertical direction (cask axial direction), rational neutron absorption performance is obtained in accordance with the vertical neutron flux characteristics of radioactive materials.

JP 2015-4576 A

By the way, in Patent Document 1, a rigid plate member and a neutron absorbing plate member are laminated without any gap in the axial direction of the cask. When the spent fuel is stored in the cask, the temperature of the basket rises and both the rigid plates and the neutron absorbing plates thermally expand. In a typical basket construction, the rigid plate material is a steel material such as stainless steel, and the neutron absorbing plate material is an aluminum material such as a boron-added aluminum alloy. Since the boron-added aluminum alloy has a higher coefficient of linear expansion than stainless steel, when both the rigid plate material and the neutron absorbing plate material thermally expand, a gap is generated between the rigid plate materials adjacent to each other in the axial direction of the cask.

The IAEA transportation regulations, which are representative transportation requirements for casks, stipulate design requirements for a 9m drop event (vertical drop, etc.). Also, even storage casks may hang vertically during cask handling, and vertical drops may occur. When the rigid plate material and the neutron absorbing plate material both thermally expand and gaps are created between the rigid plate materials adjacent to each other in the axial direction of the cask, when the cask falls vertically, the impact force generated on the basket is measured by the strength member. A neutron-absorbing plate will receive it instead of some rigid plate. In this case, buckling may occur in the neutron absorbing plate material.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a spent fuel transportation or storage cask basket that is capable of avoiding buckling of the neutron absorbing plates during vertical drop of the spent fuel transportation or storage cask.

The present invention has a basket body to be stored in a spent fuel transportation or storage cask, and the basket body has a lattice member formed in a grid shape by combining a plurality of plate-like members. Or it is formed by laminating a plurality of layers in the axial direction of the storage cask, and at least some of the plate-shaped members are composed of a rigid plate material that is a strength member and a linear expansion coefficient that is higher than that of the rigid plate material that has neutron absorption performance. The size of the neutron absorbing plate material is smaller than the size of the rigid plate material in the axial direction, and the neutron absorbing plate material is adjacent to the basket body in the entire operating temperature range in the axial direction. The mating rigid plate members are in contact with each other, and a gap is formed between some or all of the neutron absorbing plate members adjacent to each other in the axial direction.

According to the present invention, the axially adjacent rigid plate members of the spent fuel transport or storage cask are in contact with each other over the entire operating temperature range of the basket body, and the axially adjacent neutron absorbing plate members are partially or A gap is formed between them. When the spent fuel is stored in the basket body, the temperature of the basket body rises, and both the rigid plate material and the neutron absorbing plate material thermally expand. Although the coefficient of linear expansion of the neutron absorbing plate material is larger than that of the rigid plate material, gaps occur between some or all of the neutron absorbing plate materials adjacent to each other in the axial direction over the entire operating temperature range of the basket body. Therefore, the axially adjacent rigid plate members are kept in contact with each other over the entire operating temperature range of the basket body. As a result, when the spent fuel transportation or storage cask vertically drops, the rigid plate member, which is a strength member, receives the impact force generated in the basket body. Thus, it is possible to avoid buckling of the neutron absorbing plate during vertical drop of the spent fuel transportation or storage cask.

1 is a partially cutaway perspective view of a cask; FIG. 1 is a vertical cross-sectional view of a cask; FIG. FIG. 3 is a cross-sectional view taken along the line AA of FIG. 2; It is a perspective view which shows the state which is assembling the basket main body. It is the figure which looked at FIG. 4 from the C direction, and is a figure which shows the basket main body at normal temperature. FIG. 5 is a view of FIG. 4 viewed from direction C, showing the basket body in a high temperature state.

Preferred embodiments of the present invention will be described below with reference to the drawings.

(Configuration of spent fuel transport or storage cask)
A spent fuel transportation or storage cask (cask) according to this embodiment is used for transportation and storage of spent fuel. As shown in FIG. 1, which is a partially cutaway perspective view, the cask 100 has a cylindrical container body 41 with a bottom and no lid, a lid portion 42, and a trunnion 55. As shown in FIG. Also, the cask 100 accommodates the basket 1 therein. The basket 1 is formed of a plurality of grids, has an open top, and contains spent fuel 30, which is a radioactive material.

The container body 41 has a body shell 47 , an outer cylinder 45 and a neutron shield 46 . The main trunk 47 is cylindrical with a bottom and accommodates the basket 1 . The main body shell 47 is made of carbon steel, alloy steel, or stainless steel for securing gamma ray shielding function and structural strength.

The outer cylinder 45 has a cylindrical shape with a bottom, and is provided with a space on the outer side of the body shell 47 . The outer cylinder 45 is made of carbon steel or stainless steel.

The neutron shield 46 is arranged in the space between the main shell 47 and the outer cylinder 45 . The neutron shield 46 is mainly made of a material such as resin or rubber. Heat transfer fins 51 made of copper are provided between the neutron shields 46 for transferring heat from the body shell 47 to the outer cylinder 45 in order to remove the decay heat of the spent fuel 30 . A plurality of neutron shields 46 are provided in the circumferential direction of the body trunk 47, and heat transfer fins 51 are provided between adjacent neutron shields 46. As shown in FIG.

The lid portion 42 is configured to close the upper opening of the container body 41 . The lid portion 42 has a primary lid 43 and a secondary lid 44 . The primary lid 43 is disk-shaped and is attached to an opening provided above the body barrel 47 . The primary lid 43 is made of carbon steel, alloy steel or stainless steel. The outer peripheral portion of the primary lid 43 is crimped to the end face of the cask 100 via a gasket and fixed by bolting.

The secondary lid 44 is disc-shaped and attached to the outside of the primary lid 43 . As shown in FIG. 2, which is a vertical cross-sectional view of the cask 100, the secondary lid 44 is made of carbon steel, alloy steel, or stainless steel, and has an external structural member 44b and a neutron shielding member 44c. The external structural material 44b is made of carbon steel or stainless steel. The neutron shielding material 44c is arranged inside the external structural material 44b. The neutron shielding material 44c is made of a material having a high hydrogen density, such as resin or rubber.

Returning to FIG. 1, a flange is attached to the outer circumference of the end plate of the secondary lid 44 . The secondary lid 44 is crimped to the end face of the cask 100 via this flange. The secondary lid 44 is bolted and attached to the cask 100 as a sealing structure.

A seal monitoring device 52 is provided between the primary lid 43 and the secondary lid 44 . The seal monitor 52 monitors the pressure between the primary lid 43 and the secondary lid 44, which are sealed under pressure greater than 1 atmosphere, during long term storage. Then, the sealing monitoring device 52 notifies with an alarm that some kind of leak has occurred in the primary lid 43 or the secondary lid 44 by detecting a pressure drop.

As shown in FIG. 2, below the body shell 47 of the cask 100, a disc-shaped bottom plate 53 made of the same material as the body shell 47 is welded and fixed integrally with the body shell 47. As shown in FIG. A neutron shielding material 53a is attached to the outside of the bottom plate 53 while being covered with a bottom resin cover 54 to form a shielding layer.

As shown in FIGS. 1 and 2 , a plurality of trunnions 55 are attached to the outer peripheral surface of the outer cylinder 45 . The trunnions 55 are for gripping the cask 100 . The trunnion 55 is attached to the cask 100 by a transfer crane or the like to raise it upright, lay it down, lift it up and move it, or tie it down during transportation or storage. The trunnions 55 are fitted to the side surfaces of the upper end and the lower end of the body barrel 47, respectively. In this embodiment, the trunnions 55 are fitted in the body trunk 47 in the circumferential direction at intervals of 90°. Note that the installation location of the trunnion 55 is not limited to this. Also, the trunnion 55 may be fastened with a plurality of bolts.

(Basket configuration)
As shown in FIG. 3, which is a cross-sectional view taken along line AA of FIG. A basket 1 is a basket for BWR fuel, and has a basket body 2 and a support member 3 .

As shown in FIG. 4, which is a perspective view showing a state in which the basket body 2 is being assembled, the basket body 2 has a grid member 20 formed in a grid shape by combining a plurality of plate-like members 10, and the cask 100. It is formed by stacking a plurality of layers in the axial direction B. By assembling the plate-like members 10 in a grid pattern, a plurality of storage units 5 capable of storing the spent fuel 30 are formed.

A plurality of recesses 10a are formed on each of both end surfaces of the plate-like member 10 in the axial direction B so that the plate-like members 10 are fitted together when the plate-like members 10 are combined.

At least a part of the plate-like member 10 is configured by stacking a rigid plate member 11 and a neutron absorbing plate member 12 . The rigid plate material 11 is a strength member and is made of a steel material such as stainless steel. The neutron absorbing plate material 12 is made of an aluminum material such as a boron-added aluminum alloy having neutron absorbing performance. The linear expansion coefficient of the neutron absorbing plate material 12 is larger than that of the rigid plate material 11 . The rigid plate material 11 is not limited to stainless steel, and the neutron absorbing plate material 12 is not limited to boron-added aluminum alloy.

In this embodiment, part of the plate-like member 10 is configured by stacking a rigid plate member 11 and a neutron absorbing plate member 12 on top of each other. That is, as shown in FIG. 3, the plate members 10 on the outermost periphery of the cross section of the basket and on the second row from the outermost periphery are composed only of the rigid plate member 11, but the plate member 10 in the central portion is It is constructed by stacking a rigid plate material 11 and a neutron absorbing plate material 12 on top of each other. This is because the neutron absorbing plate material 12 necessary for preventing the criticality of the cask system functions effectively when it is installed in the central part of the cross section of the basket in the region where there are many adjacent fuel assemblies. At both ends of the basket body 2 that face the trunnions 55 , the rigid plate members 11 may be thicker than the central part of the basket body 2 that does not face the trunnions 55 . The reason for this is that, as will be described later, at both ends of the basket body 2 facing the trunnions 55, relatively high-energy gamma rays are emitted due to the activation of the structural materials at the upper and lower ends in the axial direction of the spent fuel assembly. Therefore, gamma ray shielding performance is more important than neutron shielding performance.

As shown in FIG. 3 , the support member 3 is arranged on the outer periphery of the basket body 2 and housed in the body trunk 47 of the container body 41 together with the basket body 2 . The support member 3 has a length extending from one end of the basket body 2 to the other end. Each plate member 10 is fixed to the support member 3 with a bolt.

As shown in FIG. 5 , which is a view of FIG. 4 viewed from direction C, the dimension of the neutron absorbing plate member 12 is smaller than the dimension of the rigid plate member 11 in the axial direction B of the cask 100 . Therefore, while the rigid plate members 11 adjacent in the axial direction B are in contact with each other, a gap a is formed between the neutron absorbing plate members 12 adjacent in the axial direction B. Here, FIG. 5 shows the basket body 2 at room temperature, and at room temperature, a gap a of about 1 mm is formed between the neutron absorbing plate members 12 adjacent to each other in the axial direction B. As shown in FIG. The dimension of this gap a is appropriately set according to the temperature of the basket body 2 and the difference in the amount of thermal expansion caused by the difference in linear expansion coefficient between the rigid plate member 11 and the neutron absorbing plate member 12, and is not limited to this size. .

In this embodiment, as shown in FIG. 5, the gap a is formed between all the neutron absorbing plate members 12 adjacent in the axial direction B, but the neutron absorbing plate members 12 adjacent in the axial direction B A gap a may be formed between a part of the . Specifically, a gap a is not formed between two neutron absorbing plate members 12 adjacent to each other in the axial direction B, and the neutron absorbing plate members 12 adjacent to these two neutron absorbing plate members 12 in the axial direction B and these two neutron absorbing plate members 12 The gap a may be alternately arranged in the axial direction B, such that the gap a is formed between two neutron absorbing plate members 12 .

When the spent fuel 30 is stored in the basket body 2, the temperature of the basket body 2 rises to about 200.degree. FIG. 6 shows a diagram of FIG. 4 viewed from direction C in a high temperature state (about 200° C.). Both the rigid plate member 11 and the neutron absorbing plate member 12 thermally expand in a high temperature state. Since the linear expansion coefficient of the neutron absorbing plate material 12 is larger than that of the rigid plate material 11, the gap a between the neutron absorbing plate materials 12 adjacent to each other in the axial direction B is smaller than 1 mm but larger than 0 mm. . Therefore, even in a high temperature state, while the rigid plate members 11 adjacent in the axial direction B are in contact with each other, a gap a is formed between the neutron absorbing plate members 12 adjacent in the axial direction B (not shown). In other words, the dimension of the neutron absorbing plate members 12 in the axial direction B is set so that the gap a is formed between the neutron absorbing plate members 12 adjacent to each other in the axial direction B even in a high temperature state. In this manner, the rigid plate members 11 adjacent in the axial direction B are in contact with each other over the entire operating temperature range of the basket body 2, and the gap a is formed between the neutron absorbing plate members 12 adjacent in the axial direction B. be.

IAEA transportation regulations, which are representative transportation requirements for the cask 100, define design requirements for a 9m drop event (vertical drop, etc.). The vertical drop of the cask 100 means that the cask 100 drops in a posture in which the central axis of the cask 100 is vertical. As in Patent Document 1, when the rigid plate material 11 and the neutron absorbing plate material 12 are stacked without gaps in the axial direction B of the cask 100, when both the rigid plate material 11 and the neutron absorbing plate material 12 thermally expand, A gap is generated between the rigid plate members 11 adjacent to each other in the axial direction B of the cask 100 . In this state, if the cask 100 falls vertically, the impact force generated in the basket body 2 will be received by the neutron absorbing plate member 12 instead of the rigid plate member 11 as a strength member. In this case, buckling may occur in the neutron absorbing plate material 12 .

On the other hand, in the present embodiment, the gap a is generated between the neutron absorbing plate members 12 adjacent in the axial direction B over the entire operating temperature range of the basket body 2. The state in which the plate members 11 are in contact with each other is maintained. As a result, when the cask 100 vertically drops, the rigid plate member 11 as a strength member receives the impact force generated in the basket body 2 . Therefore, it is possible to avoid buckling of the neutron absorbing plate member 12 when the cask 100 vertically drops.

Further, as in Patent Document 1, when the rigid plate material 11 and the neutron absorbing plate material 12 are stacked without gaps in the axial direction B of the cask 100, the bolt holes of the neutron absorbing plate material 12 are displaced in the axial direction due to thermal expansion. . Then, the end of the bolt hole interferes with the bolt, possibly deforming or damaging the bolt. Alternatively, the bolt hole may be deformed and the neutron absorbing plate material 12 may be damaged. In these cases, the rigidity of the basket body 2 cannot be maintained.

On the other hand, in this embodiment, the gap a is generated between the neutron absorbing plate members 12 adjacent to each other in the axial direction B over the entire operating temperature range of the basket body 2. deformation can be avoided. Thereby, the rigidity of the basket body 2 can be preferably maintained.

Further, as shown in FIG. 4, when a plurality of plate-like members 10 are combined, the gap formed between the recesses 10a that are fitted to each other is , is wider than the gap a formed between the neutron absorbing plate members 12 adjacent to each other in the axial direction B. As shown in FIG. In other words, the depth of the recesses 10a is adjusted so that the gap formed between the recesses 10a that are fitted to each other is wider than the gap a formed between the neutron absorbing plate members 12 that are adjacent to each other in the axial direction B. is set. Specifically, the depth of the recess 10a is greater than 1/4 of the dimension of the plate member 10 in the axial direction B. As shown in FIG. Therefore, the bottom surfaces of the recesses 10a that are fitted to each other do not come into contact with each other over the entire operating temperature range of the basket body 2 . In the embodiment shown in FIG. 4, the recesses 10a to be fitted with each other have a depth of about 1/4 from both sides of the plate-like member 10 in the axial direction B, but a depth of about 1/4 from one side of the plate-like member 10 in the axial direction B. It may be two deep.

If the bottom surfaces of the recessed portions 10a that are fitted to each other come into contact with each other, stress is concentrated on this portion, which may damage the plate-like member 10 . Therefore, stress can be prevented from concentrating on this portion by preventing the bottom surfaces of the recesses 10a that are fitted to each other from coming into contact with each other.

As shown in FIG. 2, in the axial direction B of the cask 100, in the case of BWR fuel, a structural member such as a lower tie plate is provided below the spent fuel 30, and above the spent fuel 30, Structural members such as a handle portion and an upper grid portion are provided. A spring made of stainless steel or the like is built in the upper plenum portion of the fuel rod. Structural materials provided on the lower portion and the upper portion of the spent fuel 30 differ depending on the type of the spent fuel 30 (for example, BWR fuel and PWR fuel).

In the axial direction B of the cask 100, the central portion (fuel effective portion) of the spent fuel 30 contains spent fuel pellets, which emit neutrons. The neutrons emitted from the fuel effective part of the spent fuel 30 activate the structural materials below and above the spent fuel 30 . This causes the lower and upper portions of the spent fuel 30 to emit relatively high-energy gamma rays (eg, gamma rays from ⁶⁰ Co). The lower and upper portions of the spent fuel 30 are positioned at the upper and lower end portions of the main shell 47 and face the trunnion 55 .

Therefore, the plate thickness of the rigid plate member 11 in the portion of the basket body 2 facing the trunnion 55 is made thicker than the plate thickness of the rigid plate member 11 in the other portion of the basket body 2 . As a result, a sufficient shielding thickness for shielding gamma rays can be ensured. The rigid plate members 11 adjacent to each other in the axial direction B of the cask 100 are in contact with each other over the entire operating temperature range of the basket body 2, and there is no gap between them, so that gamma rays can be suitably shielded.

(effect)
As described above, according to the spent fuel transportation or storage cask basket 1 according to the present embodiment, the rigid plate members 11 adjacent to each other in the axial direction B of the cask 100 are A gap a is formed between the neutron absorbing plate members 12 that are in contact and adjacent to each other in the axial direction B. As shown in FIG. When the spent fuel 30 is stored in the basket body 2, the temperature of the basket body 2 rises, and both the rigid plate member 11 and the neutron absorbing plate member 12 thermally expand. The linear expansion coefficient of the neutron absorbing plate material 12 is larger than that of the rigid plate material 11, but the gap a exists between the neutron absorbing plate materials 12 adjacent to each other in the axial direction B over the entire operating temperature range of the basket body 2. Therefore, the rigid plate members 11 adjacent to each other in the axial direction B are kept in contact with each other over the entire operating temperature range of the basket body 2 . As a result, when the cask 100 vertically drops, the rigid plate member 11 as a strength member receives the impact force generated in the basket body 2 . Therefore, it is possible to avoid buckling of the neutron absorbing plate member 12 when the cask 100 vertically drops.

Also, the support member 3 to which each plate member 10 is fixed with bolts is housed in the cask 100 together with the basket body 2 . When the rigid plate 11 and the neutron absorbing plate 12 are stacked without any gap in the axial direction B of the cask 100 as in Patent Document 1, the bolt holes of the neutron absorbing plate 12 are displaced in the axial direction B due to thermal expansion. Then, the end of the bolt hole interferes with the bolt, possibly deforming or damaging the bolt. Alternatively, the bolt hole may be deformed and the neutron absorbing plate material 12 may be damaged. In these cases, the rigidity of the basket body 2 cannot be maintained. On the other hand, in the entire operating temperature range of the basket body 2, since the gap a is generated between the neutron absorbing plate members 12 adjacent to each other in the axial direction B, the bolts and the bolt holes are deformed. can be avoided. Thereby, the rigidity of the basket body 2 can be preferably maintained.

Further, when a plurality of plate-like members 10 are combined, the gaps formed between the recesses 10a that are fitted to each other are equal to the axial direction B of the cask 100 when the plurality of lattice members 20 are stacked. is wider than the gap a formed between the neutron absorbing plate members 12 adjacent to each other. Therefore, the bottom surfaces of the recesses 10a that are fitted to each other do not come into contact with each other over the entire operating temperature range of the basket body 2 . If the bottom surfaces of the recessed portions 10a that are fitted to each other come into contact with each other, stress is concentrated on this portion, which may damage the plate-like member 10 . Therefore, stress can be prevented from concentrating on this portion by preventing the bottom surfaces of the recesses 10a that are fitted to each other from coming into contact with each other.

Further, the plate thickness of the rigid plate member 11 in the portion of the basket body 2 facing the trunnion 55 is made thicker than the plate thickness of the rigid plate member 11 in the other portion of the basket body 2 . The ends of the cask 100 with trunnions 55 attached thereto are located below and above the spent fuel 30 and emit relatively high energy gamma rays. Therefore, by making the plate thickness of the rigid plate member 11 in the portion facing the trunnion 55 of the basket body 2 thicker than the plate thickness of the rigid plate member 11 in the other portion of the basket body 2, the shielding thickness for shielding the gamma rays is increased. can be sufficiently secured. The rigid plate members 11 adjacent to each other in the axial direction B of the cask 100 are in contact with each other over the entire operating temperature range of the basket body 2, and there is no gap between them, so that gamma rays can be suitably shielded.

Although the embodiments of the present invention have been described above, the specific examples are merely illustrated, and the present invention is not particularly limited. Further, the actions and effects described in the embodiments of the invention are merely enumerations of the most suitable actions and effects resulting from the present invention, and the actions and effects of the present invention are described in the embodiments of the invention. are not limited to those listed.

1 Basket 2 Basket Body 3 Support Member 5 Storage Part 10 Plate-like Member 10a Recess 11 Rigid Plate Material 12 Neutron Absorption Plate Material 20 Lattice Member 30 Spent Fuel 41 Container Body 42 Lid Part 43 Primary Lid 44 Secondary Lid 45 Outer Cylinder 46 Neutron Shielding Body 47 Body trunk 51 Heat transfer fin 52 Seal monitoring device 53 Bottom plate 54 Bottom resin cover 55 Trunnion 100 Cask (spent fuel transportation or storage cask)

Claims (4)

having a basket body that is housed in a spent fuel transportation or storage cask,
The basket body is formed by stacking a plurality of grid members formed in a grid shape by combining a plurality of plate members in the axial direction of the spent fuel transportation or storage cask,
At least a part of the plate-shaped member is configured by superimposing a rigid plate material as a strength member and a neutron absorbing plate material having neutron absorption performance and a linear expansion coefficient larger than that of the rigid plate material,
In the axial direction, the dimension of the neutron absorbing plate is smaller than the dimension of the rigid plate,
Over the entire operating temperature range of the basket body, the axially adjacent rigid plate members are in contact with each other, and a gap is formed between some or all of the axially adjacent neutron absorbing plate members. A spent fuel transportation or storage cask basket characterized by: 2. The method according to claim 1, further comprising a support member arranged on the outer edge side of said basket body, each plate-shaped member being fixed with bolts, and accommodated in said spent fuel transportation or storage cask together with said basket body. A spent fuel transportation or storage cask basket as described. A plurality of recesses that are fitted to each other when the plate-like members are combined are formed on each of both end surfaces of the plate-like member in the axial direction,
When a plurality of the plate-like members are combined, the gaps formed between the recesses that are fitted to each other are such that when the plurality of lattice members are stacked, the neutrons adjacent to each other in the axial direction 3. A spent fuel transport or storage cask basket according to claim 1 or 2, wherein the basket is wider than the gap formed between the absorber plates. trunnions are attached to the sides of both ends of the spent fuel transportation or storage cask in the axial direction, respectively;
4. A plate thickness of said rigid plate member in a portion of said basket body facing said trunnion is thicker than a plate thickness of said rigid plate member in other portions of said basket body. Baskets of spent fuel transportation or storage casks as described in paragraph 1.

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