JP3207828B2 - Square pipes and baskets for casks - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention accommodates and stores spent fuel assemblies after combustion, and reduces performance concentration by reducing stress concentration on a specific portion of a square pipe constituting a basket. The present invention relates to a cask square pipe and a basket for suppressing.

[0002]

2. Description of the Related Art A nuclear fuel assembly that has been burned at the end of a nuclear fuel cycle and has become unusable is called spent nuclear fuel. Since spent nuclear fuel contains high radioactive materials such as FP, it must be thermally cooled. Therefore, the spent nuclear fuel is cooled in a cooling pit of a nuclear power plant for a predetermined period (for 3 to 6 months). Then, it is stored in a cask, which is a shielding container, and transported and stored in a truck or ship to a reprocessing facility. In storing the spent nuclear fuel assemblies in the cask, a holding frame having a lattice-like cross section called a basket is used. The spent nuclear fuel assemblies are inserted one by one into cells, which are a plurality of storage spaces formed in the basket, thereby securing an appropriate holding force against vibration during transportation.

[0003] As a conventional example of such a cask,
Various types are disclosed in "Atomic energy eye" (published on April 1, 1998: Nikkan Kogyo Shuppan Production), Japanese Patent Application Laid-Open No. 62-242725, and the like. In the following, a cask on which the present invention is based upon development of the present invention will be described. In addition, the said cask is shown for convenience of explanation, and does not correspond to what is called a well-known and public use.

FIG. 12 is a perspective view showing an example of a cask. FIG. 13 is a radial sectional view of the cask shown in FIG. The cask 500 has a cylindrical body 501.
And a resin 502 as a neutron shield provided on the outer periphery of the trunk body 501, and an outer cylinder 503, a bottom 504, and a lid 505. Body 501 and bottom 5
04 is a forged product made of carbon steel which is a γ-ray shield. The lid 505 includes a primary lid 506 and a secondary lid 507 made of stainless steel. Body 501 and bottom 504
Are joined by butt welding.

[0005] The primary lid 506 and the secondary lid 507 are fixed to the body 501 with stainless steel bolts. A metal hollow O-ring coated with aluminum or the like is interposed between the lid 505 and the body 501,
The inside is kept airtight. On both sides of the cask body 512, trunnions 5 for suspending the cask 500 are provided.
13 are provided (one is omitted). At both ends of the cask main body 512, a buffer 514 in which wood or the like is sealed as a buffer material is attached (one is omitted).

[0006] A plurality of internal fins 508 for conducting heat are provided between the trunk body 501 and the outer cylinder 503.
The inner fin 508 is made of copper to increase the heat transfer efficiency. The resin 502 is provided with the inner fin 50.
It is injected in a fluidized state into the space formed by 8 and solidified by a thermosetting reaction or the like. The basket 509 has a structure in which 69 square pipes 510 are assembled in a bundle as shown in FIG. 12, and is inserted into the cavity 511 of the trunk body 501 in a restricted state. The square pipe 510 is made of an aluminum alloy mixed with a neutron absorbing material (boron: B) so that the inserted spent nuclear fuel assembly does not reach a critical level. The accommodation space formed by each of the square pipes 510 is called a cell 515, and one cell 515 has one accommodation space.
Spent fuel assemblies can be accommodated.

[0007]

In a storage or facility, a fall accident or the like may occur during handling of the cask. Even in such a rare case, the structural integrity of the cask 500 may be reduced. , Sealing must be ensured. That is, the radiation dose emitted to the outside of the cask 500 should not exceed the specified value range even if a fall accident occurs. For this reason, cask 5
For 00, a drop test is indispensable, and it is necessary to strictly confirm whether its structural integrity and sealing performance are maintained. In addition, an accident such as a fall of the cask 500 due to an earthquake or the like is conceivable. In such a case, a structural test and a sealing performance of the cask 500 are ensured by performing a fall test in advance.

Here, when the cask 500 falls or falls, a load may be applied to the square pipe 510 constituting the basket 509 and the square pipe 510 may be damaged. FIG. 14 is a radial cross-sectional view showing a contact state of the square pipe 510. In the state where the basket 509 is formed, each square pipe 510 is in contact with the surrounding square pipe 510 on four outer surfaces (or three, two surfaces) as shown in FIG. Also, the radius R of the corner portion of the square pipe 510
Is R = (1.0 to 1.5) · t. t is the thickness of the square pipe 510.

When a load is applied to the basket 509 in the direction of arrow F in the figure due to the drop of the cask 500, the load is not transmitted straight since the corner portion of the square pipe 510 has the shape described above. (Indicated by an arrow f in the figure). For this reason, stress concentration occurs in a specific portion (regions indicated by reference symbols G and H in the figure) of the square pipe 510, and the square pipe 5
10 would cause damage or other performance degradation.
The same applies to the square pipe 510 located outside the basket (three or two outer faces of which are in contact with the adjacent square pipe 510), and also in the case of a load from an oblique direction. Also, it is considered that the load cannot be transmitted well, and thus the performance is deteriorated due to the stress concentration.

Accordingly, the present invention has been made in view of the above, and an object of the present invention is to provide a square pipe and a basket for a cask that reduce stress concentration on a specific portion of the square pipe and suppress performance deterioration. I do.

[0011]

In order to achieve the above object, a square pipe for a cask according to claim 1 constitutes a basket having grid cells by combining a plurality of square pipes and forms a grid with the grid cells. Each of the spent fuel assemblies is accommodated in a cell, and is disposed outside the square pipe.
The corner portion is formed to have a sharper edge than the inner corner portion .

When the corner portion of the square pipe has an appropriate radius R as described above, the load caused by dropping or falling of the cask is not transmitted straight to the adjacent square pipe, and as a result, stress concentrates on a specific portion of the square pipe. Will occur. Therefore, the corners of the square pipe are made sharp edges so that the load from the adjacent square pipe can be transmitted directly.

Here, the sharp edge can be said to be the same when viewed at the corner of the square pipe macroscopically, but it is generally considered not to be the sharp edge when viewed at the microscopic scale. For this reason, the sharp edge referred to here is a theoretical edge where two surfaces intersect in a macroscopic view, and is a realistic edge having a very small radius R or chamfer (C) in a microscopic view. Suppose it is an edge. In addition, the radius R and the dimension of the chamfer (C) should be interpreted as a range that realizes a sharp edge within a common sense.

The square pipe for a cask according to the second aspect has a lattice-shaped cell by combining a plurality of square pipes.
And a basket that fits
Each containing a spent fuel assembly ,
The radius of the corner portion on the outside of the square pipe is made at least half or less of the thickness of the square pipe. As a result, the range of contact with the adjacent square pipe becomes larger than half the plate thickness, so that the applied load is transmitted relatively straightforwardly to the adjacent square pipe. The dimensions of the square pipe are
It can be roughly estimated from the dimensions of the spent fuel assembly, in which case the radius of the sharp edge is 0.5
mm or less (claim 3).

According to a fourth aspect of the present invention, there is provided a square pipe for a cask, wherein the sharp edge has a chamfered shape, and the chamfered dimension is at least half or less of the thickness of the square pipe. It is. As a result, as in the above, the contact area with the adjacent square pipe becomes larger than half of the plate thickness, so that the applied load is relatively straightforwardly transmitted to the adjacent square pipe. The chamfer dimension of the sharp edge is preferably 0.5 mm or less (claim 5).

Further, the basket according to claim 6 is such that the square pipes are grouped in a columnar shape to form cells for accommodating the spent fuel assemblies in a lattice shape, and these are arranged in a cask for use. . By forming the basket using the square pipe, the load applied to the basket is transmitted straight between the square pipes, so that stress concentration on a specific portion of the square pipe is reduced. Therefore, even if the cask falls or falls, the soundness of the square pipe can be ensured, and the reliability of the basket can be improved.

Further, in the basket according to the present invention, the square pipes are arranged in a columnar shape, the cells accommodating the spent fuel assemblies are formed in a lattice shape, and the space formed by being surrounded by the corners of the square pipes. Auxiliary bodies are inserted in the cask, and these are arranged and used in a cask.

Since this corner pipe does not have the sharp edge as described above, a space is formed in the corner when the basket is assembled. For this reason, in this cask basket, a load is transmitted by inserting an auxiliary body into the space to indirectly contact the corners of the square pipe. Even with such a configuration, it is possible to reduce stress concentration on a specific portion of the square pipe.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A square pipe and a basket for a cask according to the present invention will be described below in detail with reference to the drawings. The present invention is not limited by the embodiment.

(Embodiment 1) FIG. 1 is a radial sectional view showing a square pipe according to Embodiment 1 of the present invention.
The square pipe 1 is formed by an extrusion process described later, and its size differs depending on the size of the spent fuel assembly to be housed. For example, the square pipe 1 has an outer dimension of 162 mm and an inner dimension of 151 mm in a square cross section.
Becomes Further, a corner portion of the square pipe 1 is formed into a sharp edge 2 having a radius R = 1.0 mm or less in an extrusion process.

FIG. 2 is a radial sectional view showing the abutting state of the square pipe. More specifically, when the basket 509 (see FIG. 13) is configured by assembling the square pipes 1, the square pipes 1 located at arbitrary positions of the basket 509 are shown. When a load is applied to the basket 509 in the direction of arrow F in the figure due to the dropping or falling of the cask 500, the corner portion of the square pipe 1 is formed into the sharp edge 2. 1
(Indicated by an arrow f in the figure). For this reason, it is possible to reduce the occurrence of stress concentration on a specific portion (regions G and H in FIG. 14) of the square pipe 1. This is the same for the square pipe 1 located inside the basket.

Next, the results of the drop test will be described. First, since the dimensions of the square pipe 1 are determined based on the dimensions of the spent fuel assemblies to be accommodated, the evaluation was made from the radius R with respect to the plate thickness t of the square pipe 1. Table 1 shows the evaluation results.

[0023]

[Table 1]

As a result, when the radius R was 0.8 t to 1.5 t, an undesirable stress concentration occurred at a specific portion (see FIG. 14) of the square pipe 1. When radius R = 0.6t,
Although the degree of stress concentration was reduced, it was not yet in a favorable state. Next, when the radius R was 0.4 t, the degree of stress concentration was reduced to some extent, and was within a relatively acceptable range. When the radius R was 0.05 t to 0.2 t, the stress concentration was considerably reduced, and a favorable state was obtained. In particular, good results were obtained when R = 0.1 t and 0.05 t, and the stress concentration was reduced to a level that did not cause a problem.

The sharp edge 2 formed at the corner of the square pipe 1 may have a chamfered shape. FIG. 3 is a radial cross-sectional view illustrating a modified example of the square pipe according to the first embodiment of the present invention. This chamfer dimension C is preferably set to 1.0 mm or less (dimension C = 0.2 t or less) as described above. Even with such a configuration, the basket 509
In contrast, when a load is applied in the direction of arrow F in the figure, the load is transmitted straight to the adjacent square pipe 11 (in the figure,
Indicated by arrow f). Therefore, stress concentration on a specific portion of the square pipe 11 can be reduced, and performance degradation can be suppressed.

(Embodiment 2) As shown in FIG. 4, a basket 509 in which square pipes 510 are assembled is
The round bar 31 may be fitted into the space S generated between the square pipes 510. In this way, even when a load is applied to the basket 509 in the direction of arrow F in the figure, the load is applied between the contact surfaces of the square pipes 510 and the square pipe corner 510a and the round bar 31. Since the contact portion is transmitted (indicated by an arrow f in the drawing), concentration of stress on a specific portion of the square pipe 510 can be reduced to some extent. In addition, a square bar having a square cross section may be used instead of the round bar 31.

(Embodiment 3) Next, the square pipe 1
The basket formed by using the above will be described together with the entire cask. FIG. 5 is a perspective view showing a cask according to the third embodiment of the present invention. FIG. 6 is an axial sectional view of the cask shown in FIG. FIG. 7 is a radial sectional view of the cask shown in FIG. The cask 100 has substantially the same configuration as the cask 500 shown in FIG.
There is a feature in that the shape is adapted to the outer shape of 30. The inner surface shape of the cavity 102 is formed by performing milling with a dedicated processing device described later. In addition, you may make it form by a shaper process other than a milling process.

In the cask 100 shown in FIG. 1, the body 101 and the bottom plate 104 are forged carbon steel rollers having a γ-ray shielding function. Note that stainless steel can be used instead of carbon steel. The trunk body 101
And the bottom plate 104 are joined by welding or the like. In addition, a metal gasket is provided between the lid 109 and the body 101 in order to secure the sealing performance as a pressure-resistant container.

The space between the body 101 and the outer cylinder 105 is filled with a resin 106 which is a polymer material containing a large amount of hydrogen and has a neutron shielding function. Also, the trunk body 1
A plurality of copper internal fins 107 for conducting heat are welded between the resin 106 and the outer cylinder 105.
Is injected into a space formed by the internal fins 107 in a flowing state, and is solidified by a thermosetting reaction or the like. In addition,
The internal fins 107 are preferably provided at a high density in a portion having a large amount of heat in order to uniformly radiate heat. A thermal expansion margin 108 of several mm is provided between the resin 106 and the outer cylinder 105. This thermal expansion 108
Is formed by disposing a disappearing mold in which a heater is embedded in a hot melt adhesive on the inner surface of the outer cylinder 105, injecting and solidifying the resin 106, and then heating and melting and discharging the heater (not shown).

The cover 109 includes a primary cover 110 and a secondary cover 11.
1. The primary lid 110 has a disk shape made of stainless steel or the like that blocks γ rays. The secondary lid 111 also has a disc shape made of stainless steel or the like, and a resin 112 is sealed as a neutron shield on the upper surface thereof. The primary lid 110 and the secondary lid 111 are attached to the body 101 by bolts 113 made of stainless steel. Further, metal gaskets are provided between the primary lid 110 and the secondary lid 111 and the trunk main body 101, respectively, to maintain the internal sealing performance. Also, the lid 109
Is surrounded by an auxiliary shield 115 encapsulating a resin 114.
Is provided.

On both sides of the cask main body 116, trunnions 117 for suspending the cask 100 are provided. Although FIG. 5 shows the case where the auxiliary shield 115 is provided, the auxiliary shield 115 is removed and the buffer 118 is attached when the cask 100 is transported (see FIG. 6). The buffer 118 has a structure in which a buffer 119 such as a redwood material is enclosed in an outer cylinder 120 made of a stainless steel material.

The basket 130 is composed of 69 square pipes 1 constituting a cell 131 for storing a spent fuel assembly. The square pipe 1 having the sharp edge 2 described in the first or second embodiment is used as the square pipe 1.
For the square pipe 1, an aluminum composite material obtained by adding a powder of B or B compound having neutron absorption performance to Al or Al alloy powder is used. In addition, cadmium can be used as the neutron absorber in addition to boron.

FIG. 8 is a flowchart showing a method for manufacturing the above square pipe. First, Al or an Al alloy powder is prepared by a rapid solidification method such as an atomizing method (Step S401), and a powder of B or a B compound is prepared (Step S402). Mix for minutes (step S403).

The Al or Al alloy includes pure aluminum ingot, Al-Cu-based aluminum alloy, Al-Mg
Aluminum alloy, Al-Mg-Si aluminum alloy, Al-Zn-Mg aluminum alloy, Al-F
An e-based aluminum alloy or the like can be used. Further, B ₄ C, B ₂ O ₃ or the like can be used as the B or B compound. Here, the amount of boron added to aluminum is preferably 1.5% by weight or more and 7% by weight or less. If the content is less than 1.5% by weight, a sufficient neutron absorbing ability cannot be obtained, and if the content is more than 7% by weight, the elongation with respect to tension is reduced.

Next, the mixed powder is sealed in a rubber case, and a high pressure is uniformly applied from all directions at room temperature by CIP (Cold Isostatic Press) to perform powder molding (step S).
404). CIP molding conditions are as follows: molding pressure 200MP
a, the molded product has a diameter of 600 mm and a length of 1500 m
m. By applying pressure uniformly from all directions by CIP, a high-density molded product with little variation in molding density can be obtained.

Subsequently, the powder molded product is vacuum-sealed in a can, and the temperature is raised to 300 ° C. (step S405). In this degassing step, gas components and moisture in the can are removed.
In the next step, the vacuum degassed molded product is subjected to HIP (Hot
Reforming by Isostatic Press) (Step S40)
6). The molding conditions of HIP are as follows.
The time is 30 sec, the pressure is 6000 t, and the diameter of the molded product is 400 mm. Subsequently, the outer surface and the end surface are cut to remove the can (Step S407), and the billet is hot extruded using a porthole extruder (Step S408). As the extrusion conditions in this case, the heating temperature is 500 ° C. to 520 ° C., and the extrusion speed is 5 m / min.
And The die used for the extrusion process has a sharp corner at the die because the corner of the square pipe is formed into a sharp edge.

Next, after the extrusion molding, a tensile correction is performed (Step S409), and the unsteady portion and the evaluation portion are cut to obtain a product (Step S410). As shown in FIG. 1, the completed square pipe 1 has a cross section of one side of 162 mm,
The inside has a square shape of 151 mm. As for the dimensional tolerance, a minus tolerance is set to 0 in relation to a required standard. In addition, as another manufacturing method of this square pipe 1, there is an application already filed by the applicant of the present application on May 27, 1999 (“basket and cask”). Is also good.

FIG. 9 is a perspective view showing a method of inserting the square pipe. The square pipes 1 manufactured by the above steps are sequentially inserted along the processing shape in the cavity 102.
Here, the bending and twisting of the square pipe 1 have occurred.
Since the minus tolerance of the dimension is 0, if the square pipe 1 is properly inserted, it is difficult to insert the square pipe 1 due to the accumulation of the tolerance and the bending.
Will be subjected to excessive stress. Therefore, the bending and torsion of all or some of the manufactured square pipes 1 are measured in advance by a laser measuring device or the like, and a computer is used to determine an optimum insertion position based on the measured data. In this way, the square pipes 1 can be easily inserted into the cavity 102, and the stress applied to each square pipe 1 can be made uniform.

As shown in FIGS. 9 and 7, dummy pipes 133 are respectively inserted on both sides of the square pipe row in which the number of cells is 5 or 7 in the cavity 102. This dummy pipe 133 is connected to the trunk body 101.
The object of the present invention is to reduce the weight of the body and make the thickness of the trunk body 101 uniform, and to securely fix the square pipe 1. The dummy pipe 133 is also made of a boron-containing aluminum alloy and manufactured by the same process as described above. In addition,
This dummy pipe 133 may be a simple aluminum material or may be omitted.

Next, the cavity 102 of the body 101
Will be described. FIG. 10 is a schematic perspective view showing a processing device for the cavity 102. This processing device 140
Penetrates through the inside of the trunk body 101 and
A fixed table 141 mounted and fixed in the inside, a movable table 142 sliding on the fixed table 141 in the axial direction,
A saddle 143 positioned and fixed on the movable table 142; and a spindle 14 provided on the saddle 143.
4 and a drive unit 145, and a face mill 147 provided on the spindle shaft.

On the spindle unit 146,
A reaction force receiver 148 having a contact portion formed according to the inner shape of the cavity 102 is provided. This reaction force receiver 148
It is detachable and slides along the dovetail groove (not shown) in the direction of the arrow in the figure. Further, the reaction force receiver 148 has a clamp device 149 for the spindle unit 146, and can be fixed at a predetermined position.

Further, a plurality of clamp devices 150 are mounted in the lower groove of the fixed table 141.
The clamp device 150 includes a hydraulic cylinder 151, a wedge-shaped moving block 152 provided on a shaft of the hydraulic cylinder 151, and a fixed block 153 that comes into contact with the moving block 152 on an inclined surface. The part side is attached to the inner surface of the groove of the fixed table 141. When the shaft of the hydraulic cylinder 151 is driven, the moving block 152 comes into contact with the fixed block 153, and the moving block 152 moves slightly downward by a wedge effect (indicated by a dotted line in the figure). As a result, the lower surface of the moving block 152 is pressed against the inner surface of the cavity 102, so that the fixed table 141 can be fixed in the cavity 102.

The body 101 is mounted on a rotation support table 154 composed of rollers, and is rotatable in the radial direction. In addition, the spindle unit 146 and the saddle 143
The height of the face mill 147 on the fixed table 141 can be adjusted by interposing the spacer 155 between them. The thickness of the spacer 155 is
Is the same as the dimension of one side. The saddle 143 moves in the radial direction of the body 101 by rotating a handle 156 provided on the moving table 142. Moving table 1
The movement of 42 is controlled by a servomotor 157 and a ball screw 158 provided at the end of the fixed table 141. Since the shape inside the cavity 102 changes as the processing proceeds, it is necessary to change the reaction force receiver 148 and the moving block 152 of the clamp mechanism 150 to those having an appropriate shape.

FIG. 11 is a schematic explanatory view showing a method of processing a cavity. First, the fixed table 141 is fixed to the cavity 10 by the clamp device 150 and the reaction force receiver 148.
2 is fixed at a predetermined position. Next, as shown in FIG. 7A, the spindle unit 146 is moved at a predetermined cutting speed along the fixed table 141, and the inside of the cavity 102 is cut by the face mill 147. When the cutting at the position is completed, the clamp device 150 is removed and the fixed table 141 is released.

Next, as shown in FIG. 9B, the trunk main body 101 is rotated by 90 degrees on the rotary support table 154, and the fixed table 141 is fixed by the clamp device 150. Then, cutting is performed by the face mill 147 in the same manner as described above. Thereafter, the same steps as above are further repeated twice.

Next, the spindle unit 144 is
After rotating by 0 degrees, the inside of the cavity 102 is sequentially cut as shown in FIG. Also in this case, the processing is repeated while rotating the trunk main body 101 by 90 degrees as described above. Next, as shown in FIG.
The position of the spindle unit is raised by causing the spacer 155 to bite on 44. Then, at this position, the face mill 147 is sent in the axial direction to cut the inside of the cavity 102. By repeating this while rotating it by 90 degrees, the shape necessary for inserting the square pipe 1 is almost completed. The cutting of the portion where the dummy pipe 133 is inserted may be performed in the same manner as shown in FIG. However, the spacer thickness for adjusting the height of the spindle unit 144 is the same as one side of the dummy pipe 133.

The spent fuel assemblies contained in the cask 100 include fissile materials and fission products,
Because it generates radiation and involves decay heat, the cask 1
It is necessary to ensure that the heat removal, shielding and anti-criticality functions of 00 are maintained during the storage period (about 60 years). In the cask 100 according to the first embodiment, the trunk body 101
The inside of the cavity 102 is machined so that the outside of the basket 130 formed of the square pipe 1 is inserted in a close contact state or in a state close to it (no space area).
The heat transfer surface between the square pipe 1 and the body 101 can be made large.
Further, since the inner fins 107 are provided between the body 101 and the outer cylinder 105, heat from the fuel rods is conducted to the body 101 through the square pipe 1 or the filled helium gas, and mainly the inner fins 107 are provided. Through the outer cylinder 105. As described above, since the heat of the decay heat can be efficiently removed, the temperature in the cavity 102 can be kept lower than before if the decay heat is the same.

Further, γ generated from the spent fuel assembly
The wire is a trunk body 10 made of carbon steel or stainless steel.
1, shielded by the outer cylinder 105, the lid 109, and the like.
Also, the neutrons are shielded by the resin 106 so as to eliminate the effects of radiation exposure on radiation workers. Specifically, the surface linear equivalent rate is 2 mSv / h or less,
It is designed so as to obtain a shielding function such that the dose equivalent rate of 1 m from the surface is 100 μSv / h or less. further,
Since the square pipe 1 constituting the cell 131 is made of a boron-containing aluminum alloy, it can absorb neutrons and prevent the spent fuel assembly from reaching criticality.

As described above, according to the cask 100 according to the third embodiment, since the inside of the cavity 102 of the body 101 is machined and the square pipe 1 constituting the outer periphery of the basket 130 is inserted in a tightly contacted state. The thermal conductivity from the square pipe 1 can be improved. Further, since the space area in the cavity 102 can be eliminated, the body 101 can be made compact and lightweight.
In addition, even in this case, the number of accommodated square pipes 1 does not decrease. Conversely, if the outer diameter of the trunk main body 101 is made the same as the cask shown in FIG. Specifically, in the cask 100, the number of spent fuel assemblies that can be accommodated can be increased to 69, and the cask body 1
16 has an outer diameter of, for example, 2560 mm and a weight of 120 tons.
Can be suppressed.

Since the corners of the square pipe 1 are sharp edges 2, even if the cask 100 falls or falls and a load is applied to the basket 130,
Stress concentration on a specific portion of the square pipe 1 can be reduced. Therefore, the structural integrity of the square pipe 1 is maintained, and the reliability of the cask 100 is also improved.

[0051]

As described above, according to the square pipe for a cask according to the present invention (claim 1), the square pipe
Since the outer corners have sharper edges than the inner corners, it is possible to reduce stress concentration on a specific portion of the square pipe and suppress performance degradation.

Further, according to the square pipe for a cask according to the present invention (claim 2), the outside of the square pipe is provided.
The radius of the corner was made at least half or less of the thickness of the square pipe. According to the square pipe for a cask according to the present invention (claim 4), the sharp edge has a chamfered shape, and the chamfered dimension is at least half or less of the thickness of the square pipe. For this reason, the applied load is transmitted relatively straightforwardly to the adjacent square pipe, so that stress concentration on a specific portion of the square pipe can be reduced, and performance deterioration can be suppressed. Preferably, the radius or the chamfer dimension of the sharp edge is 0.5 mm or less (claims 3 and 5).

Further, in the basket according to the present invention (claim 6), the square pipes are grouped in a columnar shape, and the cells accommodating the spent fuel assemblies are formed in a lattice shape. Stress concentration on a specific portion can be suppressed. Therefore, the soundness of the square pipe against dropping and falling of the cask is maintained, and the reliability of the basket can be improved.

Further, in the basket according to the present invention (claim 7), the square pipes are arranged in a columnar shape, the cells accommodating the spent fuel assemblies are formed in a lattice shape, and are surrounded by the corners of the square pipes. Since the auxiliary body is inserted into the formed space, the load can be transmitted through the auxiliary body. For this reason, stress concentration on a specific portion of the square pipe can be suppressed.

[Brief description of the drawings]

FIG. 1 is a radial cross-sectional view illustrating a square pipe according to a first embodiment of the present invention.

FIG. 2 is a radial sectional view showing a contact state of a square pipe.

FIG. 3 is a radial sectional view showing a modified example of the square pipe according to the first embodiment of the present invention;

FIG. 4 is a radial sectional view showing a basket according to a second embodiment of the present invention;

FIG. 5 is a perspective view showing a cask according to a third embodiment of the present invention.

FIG. 6 is an axial sectional view showing the configuration of the cask shown in FIG.

FIG. 7 is a radial sectional view showing the configuration of the cask shown in FIG. 5;

FIG. 8 is a flowchart showing a method for manufacturing a square pipe.

FIG. 9 is a perspective view showing a method of inserting a square pipe.

FIG. 10 is a schematic perspective view showing a cavity processing apparatus.

FIG. 11 is a schematic explanatory view showing a method for processing a cavity.

FIG. 12 is a perspective view showing an example of a cask.

FIG. 13 is a radial sectional view showing the configuration of the cask shown in FIG.

FIG. 14 is a radial cross-sectional view showing a contact state of a square pipe.

[Explanation of symbols]

 1 square pipe 2 sharp edge 100 cask 101 trunk body 102 cavity 104 bottom plate 105 outer cylinder 106 resin 107 internal fin 108 thermal expansion allowance 109 lid 110 primary lid 111 secondary lid 115 auxiliary shield 116 cask body 117 trunnion 118 buffer 130 Basket 131 cells

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-64-26194 (JP, A) JP-A-58-113894 (JP, A) JP-A-5-249284 (JP, A) 203398 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G21F 5/012 G21C 19/32 G21C 19/40 G21F 5/008 G21F 9/36

Claims (7)

(57) [Claims] 1. A is intended to accommodate a respective spent fuel assemblies within the lattice-like cells as well as constitute a basket having a lattice cell by combining multiple square pipe, the interior angle a outer corner portion of the square pipe A square pipe for a cask characterized by being formed with a sharper edge than the part . 2. A plurality of square pipes are combined to form a grid.
A basket having cells is formed and
Each of which contains a spent fuel assembly.
Ri, the radius of the corner portion on the outside of the corner pipe, cask square pipes, characterized in that at least half of the thickness of the square pipe or less. 3. The radius of the sharp edge is 0.5 mm.
The cask square pipe according to claim 1, wherein: 4. The sharp edge has a chamfered shape,
The square pipe for a cask according to claim 1, wherein the chamfer dimension is at least half or less of the thickness of the square pipe. 5. The sharp edge has a chamfered shape,
2. The square pipe for a cask according to claim 1, wherein the chamfer dimension is 0.5 mm or less. 6. The square pipes according to any one of claims 1 to 5 are grouped into a column to form cells accommodating the spent fuel assemblies in a grid, and these are arranged in a cask. A basket characterized by being used. 7. A square pipe is formed into a column shape to form cells for accommodating spent fuel assemblies in a lattice shape, and an auxiliary body is inserted into a space formed by being surrounded by a corner portion of the square pipe. Characterized in that a basket is used in a cask.