Metal cask basket

Abstract

To provide a basket for a metal cask that achieves reduction in material costs and suppresses a product price of the metal cask to be low.SOLUTION: A basket for a metal cask comprises: a first basket plate group 21A composed from a plurality of basket plates 21 aligned in parallel to each other toward one direction; and a second basket plate group 21B composed from a plurality of basket plates 21 aligned in parallel to each other toward a direction that is orthogonal to the one direction. The basket for a metal cask is comprised of a laminate obtained by arranging the first basket plate group and the second basket plate group in an alternately laminated manner in an axial direction. The laminate comprises: a basket plate 21 formed of a boron-added steel plate to which boron has been added; and a basket plate 21 formed of a boron-free steel plate to which boron has not been added.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a basket for a metal cask that can reduce the usage rate of neutron absorbing material. [Background technology]

[0002] A storage method using metal casks has been known as a method for safely storing spent fuel on or off the site of a nuclear power plant. A metal cask has a basket inside its shell for storing assemblies of spent fuel. The basket has a plurality of lattice-like compartments and is configured to store the assemblies of spent fuel while separating them into individual assemblies. A conventional structure for fixing a basket to a shell body is disclosed in Patent Document 1. In the metal cask of Patent Document 1, multiple grooves are formed on the inner surface of the shell body, and the basket is fixed to the shell body by inserting the ends of the basket plates constituting the basket into each groove. The basket plates in Patent Document 1 are formed from the same boron-doped steel plate that contains boron as a neutron absorbing material.

[0003] On the other hand, a basket formed by combining a basket plate made of boron-added steel plate with a basket plate made of boron-free steel plate is also known (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-171135 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-212385 Summary of the Invention [Problem to be solved by the invention]

[0005] In general, boron is a rare resource, and boron-added steel plates are special materials, so that the availability of the material is low and the price is high. The basket for a metal cask in Patent Document 2 uses boron-free steel plates in part, but because the basket plates that make up the basket have a large shape that extends over the entire axial direction of the barrel body, there is a risk that the locations where the boron-free steel plates can be used will be limited, and as a result, there is a risk that the material cost will be high.

[0006] SUMMARY OF THE INVENTION The present invention aims to solve the above-mentioned problems and provide a basket for a metal cask that can reduce material costs and keep the product price of the metal cask low. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the basket for a metal cask of the present invention is a basket for a metal cask that is provided in the shell body of a cylindrical metal cask for storing or transporting spent fuel, and that forms a plurality of lattice-like compartments for accommodating a plurality of the spent fuels, and includes a first basket plate group consisting of a plurality of basket plates aligned parallel to one another in one direction, and a second basket plate group consisting of a plurality of basket plates aligned parallel to one another in a direction perpendicular to the one direction, and is configured as a stack in which the first basket plate group and the second basket plate group are alternately stacked in the axial direction, and the stack is configured of the basket plates formed from boron-added steel plates to which boron has been added, and the basket plates formed from boron-free steel plates to which boron has not been added. At least one of the first basket plate group and the second basket plate group includes basket plates having different heights, and a stack boundary between the first basket plate group and the second basket plate group at an intermediate position in the axial direction coincides with each other. It is characterized by the presence of [Effects of the Invention]

[0008] According to the basket for a metal cask of the present invention, it is possible to reduce material costs and keep the product price of the metal cask low. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view showing a shell body and a basket to which a basket for a metal cask according to a first embodiment of the present invention is applied. [Figure 2] 2 is a diagram showing a shell body and a basket to which a basket for a metal cask according to a first embodiment of the present invention is applied, and is a schematic vertical cross-sectional view taken along line II-II in FIG. 1. FIG. [Figure 3] 1 is an exploded perspective view showing a part of the configuration of a shell body and a basket to which a basket for a metal cask according to a first embodiment of the present invention is applied. [Figure 4] 1. FIG. 2 is a diagram showing a shell body and basket to which a basket for a metal cask according to a second embodiment of the present invention is applied, and is a schematic longitudinal cross-sectional view corresponding to the cross-section along line II-II in FIG. [Figure 5] 1. FIG. 2 is a diagram showing a shell body and basket to which a basket for a metal cask according to a third embodiment of the present invention is applied, and is a schematic longitudinal cross-sectional view corresponding to the cross-section along line II-II in FIG. [Figure 6] 1. FIG. 2 is a diagram showing a shell body and a basket to which a basket for a metal cask according to a fourth embodiment of the present invention is applied, and is a schematic longitudinal cross-sectional view corresponding to the cross-section along line II-II in FIG. [Figure 7] 1. FIG. 1 is a diagram showing a shell body and a basket to which a basket for a metal cask according to a fifth embodiment of the present invention is applied, and is a schematic longitudinal cross-sectional view corresponding to the cross-section along line II-II in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. In each embodiment, the same parts are designated by the same reference numerals, and duplicated explanations will be omitted. In the description of each embodiment, the term "axial direction" refers to a direction parallel to the central axis of the cylindrical metal cask, and the term "radial direction" refers to a direction perpendicular to the axial direction. In Fig. 2 and Figs. 4 to 7, the cross section of the basket plate on the side perpendicular to the paper surface is shown as a partial cross section of the part that engages with the slit.

[0011] (First embodiment) As shown in Figure 1, a metal cask 10 is used to store or transport spent fuel assemblies 11 (hereinafter referred to as "fuel assemblies 11"; see Figure 4). Inside a barrel body (inner cylinder) 12, the metal cask 10 is provided with a metal cask basket 20 (hereinafter sometimes simply referred to as "basket 20") that has multiple compartments 13 with a lattice-like cross section for loading the fuel assemblies 11.

[0012] The trunk body 12 has the function of shielding radiation (gamma rays) generated from the fuel assemblies 11. The trunk body 12 is, for example, a cylindrical container with a bottom made of carbon steel. The outer periphery of the trunk body 12 is filled with a neutron shielding material (not shown). As shown in FIG. 3, a plurality of grooves 15 (see FIG. 3) extending in the direction of the axis O1 of the trunk body 12 (see FIG. 2) are formed on the inner surface of the trunk body 12. The plurality of grooves 15 function as insertion grooves for the basket plates 21 that constitute the basket 20. The upper opening of the trunk body 12 is closed by a plurality of cover members (not shown).

[0013] Next, the basket 20 will be described. The basket 20 has a criticality prevention function and a shielding function. As shown in Figures 2 and 3, the basket 20 has a plurality of plate-shaped basket plates 21 that are orthogonally intersected and assembled in a lattice pattern to form a plurality of compartments 13 (see Figure 1) that store the fuel assemblies 11 one by one. Each compartment 13 has a rectangular cylindrical opening in cross section (as viewed from the direction of the axial center O1 of the trunk main body 12) and is large enough to store the fuel assemblies 11.

[0014] As shown in Fig. 3, the basket 20 includes a first basket plate group 21A and a second basket plate group 21B, which are alternately stacked in the axial center O1 direction of the trunk main body 12 to form a stack (a stacked structure). As shown in Figs. 1 to 3, the first basket plate group 21A is made up of a plurality of basket plates 21 (ten in this embodiment, illustrated with reference numerals 21a to 21j) aligned parallel to one another in one direction (the vertical direction on the paper surface of Fig. 1). The second basket plate group 21B is made up of a plurality of basket plates 21 (ten in this embodiment, illustrated with reference numerals 21k to 21t) aligned parallel to one another in a direction perpendicular to the one direction (the horizontal direction on the paper surface of Fig. 1). Note that, hereinafter, the basket plates 21a to 21j and 21k to 21t may be simply referred to as basket plates 21 (each individually).

[0015] 2 and 3, the first basket plate group 21A and the second basket plate group 21B are assembled in a lattice pattern by engaging cut grooves 23 formed at the intersections of the basket plates 21 that face each other in the direction of the axis O1. Hereinafter, the stacked groups of the first basket plate group 21A will be referred to as odd-numbered groups A1 to A9 in the stacking arrangement order from the lower side (bottom side) of the trunk main body 12 in the direction of the axis O1 to the upper side (opening side) in the direction of the axis O1, as shown in Fig. 2, and the stacked groups of the second basket plate group 21B will be referred to as even-numbered groups B2 to B8 in the stacking arrangement order from the bottom side to the opening side.

[0016] The basket plates 21a-21j of the A9 group (only the basket plates 21f are shown in FIG. 2, and the same applies below) that are arranged at the top of the first basket plate group 21A in the direction of the axis O1 have a height that is approximately half that of the basket plates 21a-21j of the A3-A7 groups. Also, the basket plates 21a-21j of the A1 group that are arranged at the bottom of the first basket plate group 21A in the direction of the axis O1 have a height that is somewhat smaller than that of the basket plates 21a-21j of the A3-A7 groups.

[0017] On the other hand, in the second basket plate group 21B, the basket plates 21k-21t of the B4 to B8 groups (only the basket plates designated by the reference numeral 21p are shown in FIG. 2, and the same applies below) have the same height as the basket plates 21a-21j of the A3 to A7 groups of the first basket plate group 21A. In addition, in the second basket plate group 21B, the basket plates 21k-21t of the B2 group, which is arranged at the bottom in the direction of the axis O1, have a height that is somewhat larger than the basket plates 21k-21t of the B4 to B8 groups. In the first basket plate group 21A and the second basket plate group 21B, the height dimensions of the basket plates 21a to 21j and 21k to 21t can be appropriately changed and set for each group.

[0018] Each basket plate 21 has a rectangular shape and is provided with a plurality of engagement grooves 23 (see FIGS. 2 and 3) at equal intervals in the longitudinal direction. The intervals between the grooves 23 correspond to the width of the cross section of the fuel assemblies 11 to be stored. The depth of each groove 23 is set to an appropriate dimension, for example, about 1 / 2 to 1 / 4 of the height of each basket plate 21, so that the basket plates 21 of each group can be stacked together without any gaps in the direction of the axis O1.

[0019] The basket plates 21 of this embodiment are of two types: one formed from boron-added steel plates made of stainless steel plates containing boron (boron with high absorption capacity as a neutron absorber), and the other formed from boron-free steel plates made of stainless steel plates that do not contain boron. In other words, the stack that constitutes the basket 20 is made of basket plates 21 made of boron-added steel plates and basket plates 21 made of boron-free steel plates. The amount of boron added to the boron-added steel plates is preferably about several mass percent. 1, in the present embodiment, basket plates 21 made of boron-free steel plates are applied to basket plates 21a, 21j, 21k, and 21t that are arranged in each of the first basket plate groups 21A and each of the second basket plate groups 21B at positions that are farthest radially outward from the axis O1 of the trunk main body 12. The other basket plates 21 are basket plates 21 made of boron-added steel plates. That is, the basket plates 21a, 21j, 21k, and 21t, which are arranged in positions that are unlikely to affect the criticality prevention function and shielding function of the basket 20, are made of boron-free steel plates, thereby achieving low material costs. The boron-free steel plate is not limited to being made of stainless steel, but may be made of various materials. Here, the boron-added steel sheets are marked with a stamp indicating that boron has been added, whereas the boron-free steel sheets are not marked with a stamp, making them visually distinguishable from the boron-added steel sheets.

[0020] When assembling the basket 20 to the trunk main body 12, the basket plates 21 of group A1 are inserted into the inner surface of the trunk main body 12 along the grooves 15 (see FIG. 3 ) of the trunk main body 12. Then, the basket plates 21 are inserted in the order of group B2, group A3, and groups B4 to A9, while engaging the respective cut grooves 23. As a result, the basket plates 21 of each group are stacked in the direction of the axis O1, and the basket 20 is assembled inside the trunk main body 12.

[0021] The metal cask basket 20 of this embodiment described above includes basket plates 21a, 21j, 21k, and 21t formed from boron-free steel plates, which reduces material costs compared to a basket plate 21 made entirely from boron-added steel plates. This allows the product price of the metal cask 10 to be kept low.

[0022] In addition, the basket plates 21a, 21j, 21k, and 21t, which are formed from boron-free steel plates, are positioned at the position radially outwardly furthest from the axis O1 of the trunk main body 12, so that the criticality prevention function and shielding function of the basket 20 can be maintained in an optimal manner.

[0023] Furthermore, since the boron-added steel plates are stamped and the non-boron-added steel plates are not stamped, the basket plates 21 can be installed in the appropriate positions while visually checking these when assembling the basket 20. Therefore, incorrect installation can be prevented in advance, and installation is easy.

[0024] (Second embodiment) A metal cask basket according to a second embodiment will be described with reference to Fig. 4. Fig. 4 is a diagram showing a shell body and basket to which a metal cask basket according to the second embodiment of the present invention is applied, and is a schematic longitudinal cross-sectional view corresponding to the cross-section along line II-II in Fig. 1. The metal cask basket 20 according to this embodiment differs from the first embodiment in that basket plates 21 made of boron-free steel plates are arranged in accordance with the configuration of the fuel assembly 11, with the remaining configuration remaining unchanged.

[0025] 4, the fuel assembly 11 includes an effective fuel portion 11a, which is an area where fuel is packed, and non-effective fuel portions 11b, 11b, which are located above and below the effective fuel portion 11a and do not correspond to the effective fuel portion 11a. In the figure, the line marked with the symbol BO indicates the boundary between the effective fuel portion 11a and the non-effective fuel portion 11b.

[0026] In this embodiment, basket plates 21 made of boron-free steel plates are used for basket plates 21a-21j of groups A7 and A9 (see FIGS. 1 and 2; only basket plate 21f is shown in FIG. 4; the same applies below) and basket plates 21k-21t of group B8 (see FIGS. 1 and 2; only basket plate 21p is shown in FIG. 4; the same applies below), which are arranged corresponding to the upper non-fuel effective portion 11b. In FIG. 4, groups A7, A9, and B8 are indicated by dark dots to clearly distinguish them. The basket plates 21 arranged in the other groups A1 to A5 and B2 to B6 are made of boron-added steel plates except for the basket plates 21a, 21j, 21k, and 21t (boron-free steel plates).

[0027] Since each basket plate 21 of group B6 is a plate arranged to straddle the boundary portion BO between the upper non-effective fuel portion 11b and the effective fuel portion 11a, it is made of boron-added steel plate in consideration of the criticality prevention function and shielding function. Even when straddling the boundary portion BO in this way, if the shielding function can be ensured, each basket plate 21 in the straddling portion can also be made of boron-free steel plate.

[0028] According to the metal cask basket 20 of this embodiment described above, each basket plate 21 arranged corresponding to the non-effective fuel portion 11b on the upper side of the fuel assembly 11 is made of boron-free steel plate, which makes it possible to reduce material costs. This allows the product price of the metal cask 10 to be kept low.

[0029] Furthermore, since the basket plate 21 formed of a boron-free steel plate is disposed in the non-active fuel portion 11b on the upper side of the fuel assembly 11, the criticality prevention function and shielding function of the basket 20 can be suitably maintained.

[0030] (Third embodiment) A metal cask basket according to a third embodiment will be described with reference to Figure 5. Figure 5 is a diagram showing a shell body and basket to which a metal cask basket according to a third embodiment of the present invention is applied, and is a schematic longitudinal cross-sectional view corresponding to the cross-section along line II-II in Figure 1. The metal cask basket 20 of this embodiment differs from the second embodiment in that basket plates 21 formed from boron-doped steel plates with different boron doping rates (hereinafter referred to as "basket plates 21 with different doping rates") are arranged in accordance with the configuration of the fuel assembly 11, with the other configuration remaining unchanged. In Figure 5, a light dot pattern is applied to the group in which basket plates 21 with different doping rates are arranged.

[0031] As shown in Fig. 5, the basket plates 21 with different additive rates are applied to the basket plates 21k to 21t of the B6 group (see Figs. 1 and 2, only the one designated by reference numeral 21p is shown in Fig. 5, the same applies below) that are arranged on the upper side of the basket 20, straddling the boundary portion BO between the effective fuel portion 11a and the non-effective fuel portion 11b of the fuel assembly 11. Also, the basket plates 21 with different additive rates are applied to the basket plates 21a to 21j of the A1 group (see Figs. 1 and 2, only the one designated by reference numeral 21f is shown in Fig. 5, the same applies below) that are arranged on the lower side of the basket 20, straddling the boundary portion BO between the effective fuel portion 11a and the non-effective fuel portion 11b. In other words, the basket plates 21 with different additive rates are arranged only in the boundary portion BO between the effective fuel portion 11a and the non-effective fuel portion 11b of the fuel assembly 11 and in the region near the boundary portion BO (regions where the neutron dose equivalent rate is relatively small).

[0032] The basket plates 21 with different additive rates have a smaller boron additive rate (smaller boron additive amount) than the basket plates 21 made of boron-added steel plates other than those in the effective fuel portion 11a. The basket plates 21 with different additive rates are marked with markings that are different from the markings marked on the boron-added steel plates, allowing them to be visually distinguished during assembly.

[0033] According to the metal cask basket 20 of this embodiment described above, each basket plate 21 arranged corresponding to the upper non-effective fuel portion 11b of the fuel assembly 11 is made of boron-free steel plate, and in addition, each basket plate 21 of the B6 group and the A1 group arranged at a position straddling the upper-lower boundary portion BO is made of boron-added steel plate with a different (smaller) boron addition rate. Therefore, it is possible to achieve optimal shielding function in the region where the neutron dose equivalent rate is relatively small near the upper-lower boundary portion BO, while maintaining criticality prevention function and achieving low material costs. This allows the product price of the metal cask 10 to be kept lower.

[0034] (Fourth embodiment) A metal cask basket according to a fourth embodiment will be described with reference to Fig. 6. Fig. 6 is a diagram showing a shell body and a basket to which a metal cask basket according to a fourth embodiment of the present invention is applied, and is a schematic longitudinal cross-sectional view corresponding to the cross-section along line II-II in Fig. 1. The metal cask basket 20 according to this embodiment differs from the first to third embodiments in that the stacking boundary between the first basket plate group 21A and the second basket plate group 21B is set so as to correspond to the boundary portion BO of the fuel assembly 11; the rest of the configuration is the same. In Fig. 6, a dark dot pattern is applied to the group in which basket plates 21 made of boron-free steel plates are arranged.

[0035] As shown in Fig. 6, the first basket plate group 21A includes basket plates 21a to 21j (see Figs. 1 and 2, only the one designated by reference numeral 21f is shown in Fig. 6, the same applies below) of the A3a group and the A3 group to the A7a group corresponding to the active fuel portion 11a of the fuel assembly 11. The first basket plate group 21A also includes basket plates 21a to 21j (see Figs. 1 and 2, only the one designated by reference numeral 21f is shown in Fig. 6, the same applies below) of the A1a group corresponding to the non-active fuel portion 11b on the lower side of the fuel assembly 11. The first basket plate group 21A also includes basket plates 21a to 21j (see Figs. 1 and 2, only the one designated by reference numeral 21f is shown in Fig. 6, the same applies below) of the A9a group and the A11a group corresponding to the non-active fuel portion 11b on the upper side of the fuel assembly 11.

[0036] On the other hand, the second basket plate group 21B includes basket plates 21k-21t (see FIGS. 1 and 2; only the one designated by reference numeral 21p is shown in FIG. 6, and the same applies below) of the B4b group to the B6 group corresponding to the active fuel portion 11a of the fuel assembly 11. The second basket plate group 21B also includes basket plates 21k-21t (see FIGS. 1 and 2; only the one designated by reference numeral 21p is shown in FIG. 6, and the same applies below) of the B2b group corresponding to the non-active fuel portion 11b on the lower side of the fuel assembly 11. The second basket plate group 21B also includes basket plates 21k-21t (see FIGS. 1 and 2; only the one designated by reference numeral 21p is shown in FIG. 6, and the same applies below) of the B8b group corresponding to the non-active fuel portion 11b on the upper side of the fuel assembly 11.

[0037] The basket plates 21a-21j of the A3a and A7a groups corresponding to the active fuel portion 11a of the fuel assembly 11 have height dimensions that are approximately half that of the basket plates 21a-21j of the A3-A5 groups. Note that the basket plates 21k-21t of the B4b-B6 groups corresponding to the active fuel portion 11a are similar to the basket plates 21 of the A3-A5 groups.

[0038] In contrast, the basket plates 21 of the A1a group, A9a group, A11a group, B2b group, and B8b group, which correspond to the non-effective fuel portion 11b of the fuel assembly 11, are set to have height dimensions corresponding to the region of the non-effective fuel portion 11b. By configuring them in this manner, the stacking boundary between the first basket plate group 21A and the second basket plate group 21B is aligned with the boundary portion BO.

[0039] In this embodiment, basket plates 21 made of boron-free steel plates are used for basket plates 21a-21j arranged in the A9a and A11a groups, and basket plates 21k-21t arranged in the B8b group, which are arranged corresponding to the upper non-fuel effective portion 11b. Also, basket plates 21 made of boron-free steel plates are used for basket plates 21a-21j arranged in the A1a group, and basket plates 21k-21t arranged in the B2b group, which are arranged corresponding to the lower non-fuel effective portion 11b. In FIG. 6, the A9a, A11a, B8b, A1a, and B2b groups are clearly indicated by dark dots. The remaining basket plates 21 arranged in the A3a to A7a groups and the B4b to B6 groups are made of boron-added steel plates, except for basket plates 21a, 21j, 21k, and 21t (boron-free steel plates).

[0040] According to the metal cask basket 20 of the present embodiment described above, the stacking boundary between the first basket plate group 21A and the second basket plate group 21B and the boundary portion BO are aligned, so that the basket plates 21 made of boron-free steel plates and boron-added steel plates can be arranged efficiently. This makes it possible to reduce material costs and keep the product price of the metal cask 10 low.

[0041] Furthermore, since basket plates 21 made of boron-free steel plates are arranged in the non-effective fuel portions 11b on the upper and lower sides of the fuel assembly 11, the criticality prevention function and shielding function of the basket 20 can be maintained in an optimal manner.

[0042] (Fifth embodiment) A fifth embodiment of the basket for a metal cask will be described with reference to Figure 7. Figure 7 is a diagram showing a shell body and basket to which a basket for a metal cask according to the fifth embodiment of the present invention is applied, and is a schematic longitudinal cross-sectional view corresponding to the cross-section along line II-II in Figure 1. The basket for a metal cask 20 of this embodiment differs from the fourth embodiment in that basket plates 21 with different additive rates are arranged, but the other configurations are the same. In Figure 7, a light dot pattern is applied to the group in which basket plates 21 with different additive rates are arranged.

[0043] As shown in Fig. 7, the basket plates 21 with different additive rates are applied to basket plates 21a to 21j (see Figs. 1 and 2; only the one with reference numeral 21f is shown in Fig. 7, the same applies below) of the A3a and A7a groups that are arranged in the active fuel portion 11a adjacent to the boundary portion BO of the fuel assembly 11. In other words, the basket plates 21 with different additive rates are arranged in the region near the boundary portion BO of the fuel assembly 11 (the region where the neutron dose equivalent rate is relatively small).

[0044] The basket plates 21 with different additive rates have a smaller boron additive rate (smaller boron additive amount) than the basket plates 21 made of boron-added steel plates other than those in the effective fuel portion 11a. The basket plates 21 with different additive rates are marked with markings that are different from the markings marked on the boron-added steel plates, allowing them to be visually distinguished during assembly.

[0045] According to the metal cask basket 20 of this embodiment described above, each basket plate 21 arranged corresponding to the non-effective fuel portion 11b of the fuel assembly 11 is made of boron-free steel plate, and in addition, each basket plate 21 of the A3a group and the A7a group adjacent to the boundary portion BO is made of boron-added steel plate with a different (smaller) boron addition rate. Therefore, it is possible to achieve a shielding function in the region near the boundary portion BO where the neutron dose equivalent rate is relatively small, while maintaining the criticality prevention function and achieving low material costs. This allows the product price of the metal cask 10 to be kept lower. If the shielding function can be ensured, the basket plates 21 of the B4b group and the B6 group adjacent to the boundary portion BO can be set to boron-added steel plates with different addition rates.

[0046] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and each component can be appropriately modified within the scope of the invention. For example, in the first, second, and fourth embodiments, one type of basket plate 21 made of boron-doped steel plate is used, but the present invention is not limited to this, and one or more types of basket plates 21 with different doping rates may be used for each group. Also, in the third and fifth embodiments, groups are provided in which basket plates 21 with different doping rates are arranged, but in addition to this, one or more types of basket plates 21 with different doping rates may be used for each group. In these cases, it is preferable to arrange basket plates 21 with different doping rates in accordance with the neutron dose equivalent rates of the fuel assemblies 11 to be housed. By configuring in this way, it is possible to more suitably achieve a reduction in material costs while maintaining the shielding function and the criticality prevention function.

[0047] In addition, in the second to fifth embodiments, the basket plates 21a, 21j, 21k, and 21t are made of boron-free steel plates, but this is not limited to this, and boron-added steel plates or basket plates 21 with different addition rates may also be used.

[0048] In each embodiment, the number of basket plates 21 installed in each group, the height dimension, etc. can be set as appropriate. [Explanation of symbols]

[0049] 10 Metal Cask 11 Fuel assembly (assembly of spent fuel) 11a Effective fuel section 11b Non-fuel effective part 12 Body 13 Compartment 20 Metal cask basket (basket, laminate) 21 Basket Plate 21A First basket plate group 21B Second basket plate group BO boundary O1 axis center

Claims

1. A metal cask basket that is provided in a shell body of a cylindrical metal cask for storing or transporting spent fuel, and that forms a plurality of lattice-shaped compartments for storing a plurality of the spent fuel, a first basket plate group including a plurality of basket plates aligned parallel to one another in one direction; a second basket plate group including a plurality of basket plates aligned parallel to one another in a direction perpendicular to the one direction, the basket plate group is configured as a stacked body in which the first basket plate group and the second basket plate group are alternately stacked in the axial direction, the laminated body includes the basket plate formed of a boron-doped steel plate to which boron is added, and the basket plate formed of a boron-free steel plate to which boron is not added, A basket for a metal cask, characterized in that at least one of the first basket plate group and the second basket plate group includes basket plates having different height dimensions, and a stacking boundary between the first basket plate group and the second basket plate group at an intermediate portion in the axial direction coincides.

2. The basket for a metal cask according to claim 1, A basket for a metal cask, characterized in that the basket plate located at the radially outermost position from the axis of the metal cask among the plurality of basket plates is made of the boron-free steel plate.

3. The basket for a metal cask according to claim 1, The metal cask basket is characterized in that the boron-free steel plates have different boron addition rates for the first basket plate group and the second basket plate group.

4. The basket for a metal cask according to claim 1, The spent fuel has an effective fuel portion in which fuel is packed and a non-effective fuel portion that does not correspond to the effective fuel portion, the plurality of basket plates of the first basket plate group and the second basket plate group, which are arranged at positions corresponding to the effective fuel portions, are made of the boron-added steel plates, A basket for a metal cask, characterized in that the plurality of basket plates of the first basket plate group and the second basket plate group, which are arranged at positions corresponding to the non-fuel effective portion, are made of the boron-free steel plate.

5. The basket for a metal cask according to claim 4, the plurality of basket plates of the first basket plate group and the second basket plate group are disposed at positions corresponding to boundaries between the fuel effective portion and the non-fuel effective portion, A basket for a metal cask, characterized in that the plurality of basket plates are made of boron-doped steel plates having a lower boron doping rate than the plurality of basket plates arranged at positions corresponding to the effective fuel portion.

6. The basket for a metal cask according to claim 1, The spent fuel has an effective fuel portion in which fuel is packed and a non-effective fuel portion that does not correspond to the effective fuel portion, A basket for a metal cask, characterized in that the stacking boundary between the first basket plate group and the second basket plate group is set to correspond to the boundary between the fuel effective portion and the non-fuel effective portion.

7. The basket for a metal cask according to claim 6, the plurality of basket plates of the first basket plate group and the second basket plate group, which are arranged at positions corresponding to the effective fuel portions, are made of the boron-added steel plates, A basket for a metal cask, characterized in that the plurality of basket plates of the first basket plate group and the second basket plate group, which are arranged at positions corresponding to the non-fuel effective portion, are made of the boron-free steel plate.

8. The basket for a metal cask according to claim 7, A basket for a metal cask, characterized in that the plurality of basket plates made of boron-doped steel plates arranged at positions corresponding to the fuel effective portion have different boron doping rates for each of the first basket plate group and the second basket plate group.

9. The basket for a metal cask according to claim 7, A basket for a metal cask, characterized in that, of the plurality of basket plates of the first basket plate group and the second basket plate group that are arranged at positions corresponding to the fuel effective portion, the plurality of basket plates adjacent to the boundary portion are made of boron-doped steel plate having a lower boron doping rate than the plurality of basket plates that are arranged at positions corresponding to the other fuel effective portion.

10. The basket for a metal cask according to claim 7, A basket for a metal cask, characterized in that among the plurality of basket plates of the first basket plate group and the second basket plate group that are arranged at positions corresponding to the fuel effective portion, the basket plate that is arranged at a position farthest radially outward from the axis of the metal cask is made of the boron-added steel plate.

11. The basket for a metal cask according to claim 1, A basket for a metal cask, characterized in that the boron-added steel plate is stamped with a mark indicating that boron has been added.

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