JP2016191570A - Supporting/fixing device for cask basket - Google Patents

Abstract

PROBLEM TO BE SOLVED: To absorb thermal stress generated by decay heat.SOLUTION: A supporting/fixing device for a cask basket includes: a bundle body 40 in which a plurality of square pipes 41 are disposed with their side faces facing each other; a plurality of outer periphery restraining members 51-53 that are externally fitted around the outer periphery of the bundle body 40 along the whole circumference and disposed at prescribed intervals apart in the bundle body axis direction O; and a plurality of coupling rails 60 that are disposed around the outer periphery of the outer periphery restraining members 51-53 along the bundle body axis direction O and couple all the outer periphery restraining members 51-53 with each other via coupling mechanisms 80. All the outer periphery restraining members 51-53 or all parts excluding one bottom plate 53 are configured to slide in the bundle body axis direction O within a tolerance range of thermal expansion length of the bundle body 40.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a basket support and fixing device for supporting and fixing a square pipe that accommodates a spent nuclear fuel assembly in a cask for transporting and storing the spent nuclear fuel assembly.

  Spent nuclear fuel assemblies (hereinafter referred to as fuel assemblies) removed from the nuclear reactor are stored in, for example, a storage pool in the reactor building in order to keep emitting radiation and generate decay heat of the fuel assemblies. . When transporting or storing a fuel assembly, a cask is used to prevent an excessive temperature rise due to radiation leakage or decay heat. The cask has a function of shielding radiation and a heat removal function for dissipating decay heat and suppressing temperature rise, and it is required to have strong strength so as not to be damaged.

  In order to secure these functions, the conventional cask protects the bundle 101 as shown in FIG. 5, a square pipe 100 that houses spent nuclear fuel rods, a bundle 101 that is a bundle of square pipes 100. The fuselage 102, the neutron shield 103 that covers the fuselage 102 and shields neutron radiation, the outer shell casing 106 with the heat removal fin 104 that releases heat at the outermost periphery, and both ends of the fuselage should be dropped. And a shock absorber 105 that absorbs the impact of dropping.

  For example, in Patent Document 1, a disk in which a plurality of holes into which a square pipe is fitted is formed at upper, lower, left, and right positions is arranged at regular intervals, and is connected by four clamping rods, and is a spacer that is externally fitted to the clamping rods. Holds the distance between the disks. This structure ensures sufficient heat dissipation of decay heat from spent nuclear fuel and strength to withstand impacts such as dropping.

Japanese Patent No. 4406990

However, it was necessary to relieve the thermal stress generated by the decay heat in the cask.
It is an object of the present invention to provide a basket support and fixing device that can absorb thermal stress generated by decay heat from spent nuclear fuel.

In order to achieve this object, the invention according to claim 1
A supporting and fixing device for a cask basket for transporting or storing spent nuclear fuel assemblies,
A bundle in which a plurality of square pipes are arranged with the side surfaces facing each other;
A plurality of outer peripheral restraining members that are fitted over the outer periphery of the bundle over the entire circumference and arranged at predetermined intervals in the bundle axial direction;
A plurality of connecting rails arranged along the bundle axis direction on the outer periphery of the outer peripheral restraining member, and connecting all the outer peripheral restraining members to each other via a connecting mechanism;
All of the above-mentioned connecting mechanisms or all except one outer peripheral restraining member are configured to be slidable in the bundle axis direction within the allowable range of the thermal expansion length of the above-mentioned bundle.

The invention according to claim 2 is a support and fixing device for a cask basket according to claim 1,
The coupling mechanism is
A fitting portion formed on each of the outer periphery restraining members;
A fitting portion that is formed on the connecting rail and is fitted to allow the fitting portion to slide in the axial direction of the bundle in the range of the thermal expansion length of the square pipe;
It has the fastener which connects the said fitting part and the said insertion part so that sliding is possible in the range of the said thermal expansion length, It is characterized by the above-mentioned.

The invention according to claim 3 is a support and fixing device for a cask basket according to claim 1 or 2,
A heat removal block is arranged between adjacent connecting rails, the square pipe and the heat removal block are made of aluminum alloy,
The connecting rail is made of carbon steel or stainless steel.

The invention according to claim 4 is a cask basket support and fixing device according to any one of claims 1 to 3,
The outer periphery restraining member is composed of a top plate disposed at the upper end of the bundle, a bottom plate disposed at the lower end of the bundle, and an intermediate plate disposed between the top plate and the bottom plate.
The fitting portion of the connecting rail into which the fitting portion of the top plate is fitted has an L-shaped groove shape in a side view with the upper end opened, and the fitting portions of the bottom plate and the intermediate plate are fitted respectively. The insertion portion of the connecting rail is characterized by having a side view angular groove shape.

The invention according to claim 5 is a support and fixing device for a cask basket according to claim 4,
The connection mechanism between the bottom plate and the connection rail is tightly coupled, and the connection mechanism between the intermediate plate and the connection rail is slidable within the range of the thermal expansion length of the square pipe from the bottom frame to the intermediate plate. It is a feature.

  According to the invention of claim 1, the outer peripheral restraining member that holds the bundle is connected to the connection rail via a connection mechanism that is slidable in the bundle axis direction within the range of the thermal expansion length of the bundle. It can absorb the stress that the bundles extend in the axial direction due to the thermal expansion of the square pipe, and can effectively absorb the thermal stress in the bundle axis direction that occurs in the square pipe caused by the spent nuclear fuel. it can.

According to the invention which concerns on Claim 2, since it was set as the structure which supports a load by a fitting part and a fitting part in a connection mechanism, a shear stress does not arise in a fastener.
According to the third aspect of the invention, even in the case of a square pipe having a high coefficient of thermal expansion, the outer peripheral restraining member can be slid within the range of the thermal expansion length via the coupling mechanism. Thermal stress can be absorbed. Further, the strength can be sufficiently ensured by the high-strength steel outer peripheral restraining member and the connecting rail. Furthermore, the square pipe and the heat removal block having a high coefficient of thermal expansion can effectively dissipate the decay heat and improve the heat removal performance.

  According to the invention which concerns on Claim 5, the load at the time of hanging cask can be supported by a bottom plate directly via a connection rail, and can be carried stably.

It is a partially cutaway perspective view showing an example of a support and fixing device for a cask basket according to an embodiment of the present invention. (A)-(f) shows an outer periphery restraint member, (a) is a top view of a top plate, (b) is a top view of an intermediate plate, (c) is a top view of a bottom plate, (d) is (a) (A) is a side view of the intermediate plate, (f) is a BB cross-sectional view shown in (c). (A) And (b) shows a connection rail, (a) is a front view, (b) is a longitudinal cross-sectional view. (A) And (b) is a cross-sectional view which shows the assembly procedure of a support fixing device, (a) shows before assembly, (b) shows after assembly. It is a partial cross section perspective view which shows the structure of the conventional cask.

A cask basket supporting and fixing device (hereinafter referred to as a supporting and fixing device) according to an embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 1, the cask is provided with a bundle 40 in which a plurality of square pipes 41 for accommodating spent nuclear fuel assemblies (hereinafter referred to as fuel assemblies) are arranged with their side surfaces facing each other. Yes. A plurality of outer peripheral restraining members 50 (four in the figure, 51, 52, 52, and 53 in the figure) that are externally fitted to the outer peripheral portion of the bundle 40 are spaced at a predetermined interval in the bundle axial direction O. Are arranged. In the outer peripheral portions of these outer peripheral restraining members 50, a plurality of connecting rails 60 for connecting the outer peripheral restricting members 50 to each other are bundled at a substantially constant interval in the circumferential direction on the outer peripheral portion of the outer peripheral restricting member 50. It is arranged along the body axis direction O. And these connection rail 60 and the outer periphery restraint member 50 are connected via the connection mechanism 80 which can absorb the stress by thermal expansion. A plurality of heat removal blocks 70 that restrain the outer peripheral portion of the bundle 40 are arranged at the outer peripheral portion of the bundle 40 and between the adjacent connecting rails 60 and between the adjacent outer peripheral restraining members 50.

  The square pipe 41 is formed in a rectangular (square) cross section, and the material thereof is boron added with samarium (Sn), which is a neutron absorber, or an aluminum alloy containing a boron compound. The outer periphery restraining member 50 is used as a strength member such as carbon steel or stainless steel. Note that the below-described top plate 51 having a small load may be made of an aluminum alloy. The heat removal block 70 is made of an aluminum alloy or a laminated body of aluminum alloy plates having a high heat transfer rate and high heat removal performance.

[Outer circumference restraining member]
The outer periphery restraining member 50 includes a top plate 51 that is an upper end when the cax is erected, a bottom plate 53 that is a lower end, and an intermediate plate 52 that is disposed between the top plate 51 and the bottom plate 53. The intermediate plate 52 is composed of an upper intermediate plate 21 and a lower intermediate plate 22 that are arranged vertically at a predetermined interval. The lower end of the bundle 40 is supported from below by the bottom plate 53, the upper end of the bundle 40 is pressed from above by the top plate 51, and the intermediate portion of the bundle 40 is restrained by the intermediate plate 52. ing.

  As shown in FIGS. 2A and 2D, the top plate 51 is formed in an annular disk shape, and the opening 11 is formed corresponding to the upper end of the bundle 40. A lattice-shaped pressing frame 12 that holds the upper end of the square pipe 41 is provided in the openings 11. Further, four first fitting portions 13 for fitting the connecting rails 60 are formed on the outer peripheral portion of the top plate 51 with an interval of 90 °. A screw hole 13 a is formed in the radial direction on the front surface of each first fitting portion 13.

  As shown in FIGS. 2B and 2E, the intermediate plate 52 is formed in an annular disk shape surrounding the bundle 40, and the upper intermediate plate 21 and the lower intermediate plate 22 have the same shape. Only the description of the lower intermediate plate 22 will be omitted. The names in parentheses are the names of the lower intermediate plate 22.

  The upper intermediate plate 21 has an opening 23 into which the outer periphery of the bundle 40 is fitted. In addition, four second fitting portions 24 (third fitting portions 25) for fitting the connecting rails 60 are formed on the outer peripheral portion of the upper intermediate plate 21 with an interval of 90 °. A screw hole 24a (25a) is formed in the radial direction in front of the second fitting portion 24 (third fitting portion 25).

  As shown in FIGS. 2C and 2F, the bottom plate 53 is formed in an annular disk shape, and an opening 31 is formed corresponding to the lower end of the bundle 40, and the square pipe 41 is formed in these openings 31. A grid-like support frame 32 is provided to support the lower end of the frame from below. The bottom plate 53 is formed with four fourth fitting portions 33 for fitting the connecting rails 60 at intervals of 90 ° on the outer peripheral portion. A screw hole 33a is formed in the radial direction on the front surface of the fourth fitting portion 33.

[Connection rail]
As shown in FIG. 3, the connecting rail 60 is a strength member made of stainless steel or carbon steel and has a rectangular cross section. Further, the connecting rail 60 may be formed of an alloy steel obtained by adding boron or a boron compound to stainless steel, or an alloy steel obtained by adding gadolinium (Gd).

  On the inner surface of the connecting rail 60, a first fitting part 61 into which the first fitting part 13 is fitted, a second fitting part 62 into which the second fitting part 24 is fitted, and a third A third fitting portion 63 into which the fitting portion 25 is fitted and a fourth fitting portion 64 into which the fourth fitting portion 33 is fitted are formed.

  The first insertion portion 61 is cut out in an L shape in a side view with the upper end opened. The second insertion portion 62, the third insertion portion 63, and the fourth insertion portion 64 are each cut out in a square groove shape when viewed from the side. Further, a hole 64a with a counterbore for fitting a fastening bolt 64b, which is a fastener, is formed in the fourth fitting portion 64 from the front surface to the cutout bottom surface. Further, in the first to third insertion portions 61 to 63, countersunk long holes 61a to 63a for fitting fastening bolts 61b to 63b serving as fasteners are provided in the length direction from the front surface to the cutout bottom surface. It has been drilled.

[Coupling mechanism]
The connecting mechanism 80 will be described with reference to FIGS. 3 and 4.
In this embodiment, the fourth fitting portion 64 of the connecting rail 60 is closely fitted with the fourth fitting portion 33 of the bottom plate 53, and the slide width δ4 at the fourth fitting portion 64 is set to zero. ing.

  A slide width: δ3 that allows the third fitting portion 25 to slide in the third fitting portion 63 is provided in the length direction. Further, a slide width: δ2 that allows the second fitting portion 24 to slide in the second fitting portion 62 is provided in the length direction. Here, these slide widths are set to δ4 (= 0) <δ3 <δ2 <δ1 (= ∞). Since the upper end of the first insertion portion 61 is open, the slide width is ∞.

  And in the connection mechanism 80, the 1st-4th fitting parts 13, 24, 25, 33 of the outer periphery restraint member 50 are each fitted by the 1st-4th fitting parts 61-64 of the connection rail 60, and fastening. The bolts 61b to 64b are fitted into the screw holes 13a, 24a, 25a, and 33a through the long holes 61a to 64a and the holes 64a, respectively, and tightened, whereby the four outer peripheral restraining members 50 fitted to the bundle 40 are Assemble the four fastening rods 60.

  More specifically, in the first insertion portion 61, the thermal expansion of the connecting rail 60 at the distance L1 from the thermal expansion length of the square pipe 41 at the distance L1 from the fourth insertion portion 64 to the first insertion portion 61. The slide width δ1 is obtained by subtracting the length. In the second insertion portion 62, the thermal expansion length of the connecting rail 60 at the distance L2 is subtracted from the thermal expansion length of the square pipe 41 at the distance L2 from the fourth insertion portion 64 to the second insertion portion 62. Thus, the slide width δ2 is obtained. Further, in the third insertion portion 63, the thermal expansion of the connection rail 60 at the distance L3 is determined from the thermal expansion length of the square pipe 41 at the distance L3 from the fourth insertion portion 64 of the connection rail 60 to the third insertion portion 63. The slide width δ3 is obtained by subtracting the length. Further, the lengths of the long holes 62a to 63a in the first to third insertion portions 61 to 63 are set corresponding to the slide widths δ1 to δ3. Here, the heating temperature by the decay heat of the fuel assembly is, for example, 300 to 400 ° C.

  When the fuel assembly is not accommodated, the connecting rail 60 and the bottom plate 53 are connected and fixed, that is, when not heated by decay heat, the load applied when the cask is suspended is applied from the connecting rail 60 to the fourth fitting portion 64 and the fourth insertion portion 64. It is transmitted to the bottom plate 53 through the fitting part 33, and the cask can be stably supported.

  When the fuel assembly accommodated in the square pipe 41 is heated by the decay heat of the fuel assembly, the second and third fitting portions 62 and 63 cause the first insertion due to the difference in thermal expansion length between the square pipe 41 and the connecting rail 60. Since the second and third fitting portions 24 and 25 are slid upward and are in contact with the upper surface walls of the second and third fitting portions 62 and 63, the thermal stress generated by the decay heat of the fuel assembly is reduced. Can be absorbed. When the cask is suspended, the load applied when the cask is suspended passes from the connecting rail 60 through the second to fourth fitting portions 62 to 64 and the second to fourth fitting portions 24, 25, and 33. Although transmitted to the plate 21, the lower intermediate plate 22 and the bottom plate 53, the upper side surfaces of the second to fourth fitting portions 24 to 33 are brought into contact with the upper surface walls of the second to fourth fitting portions 62 to 64. The cask can be stably supported without applying a shearing force to the fastening bolts 62b to 64b. Of course, at this time, a shearing force is applied to the fastening bolt 61b of the first fitting portion 61. However, this shearing force only needs to support the weight of the top plate 51, and can be sufficiently supported by the fastening bolt 61b.

[Effect of the embodiment]
According to the above embodiment, the outer peripheral restraining member 50 that holds the bundle 40 is connected to the connection rail 60 via the connection mechanism 80 that is slidable in the bundle axial direction O within the range of the thermal expansion length of the bundle 40. Since they are connected, the stress extending in the bundle axial direction O due to the thermal expansion of the square pipe 41 can be absorbed, and the thermal stress in the bundle axial direction O generated in the square pipe 41 generated by the spent nuclear fuel assembly. Can be effectively absorbed.

  Further, in the coupling mechanism 80, since the load is supported by the second to fourth fitting portions 62 to 64 and the second to fourth fitting portions 24, 25 and 33, the fastening bolts 62b to 64b are sheared. There is no load.

  Further, even in the case of the square pipe 41 made of an aluminum alloy having a high thermal expansion coefficient, the outer peripheral restraining member 50 is slidable within the range of the thermal expansion length via the coupling mechanism 80, and thus is generated by the thermal expansion of the decay heat. The thermal stress in the bundle axis direction O can be absorbed. Further, the strength can be sufficiently ensured by the steel outer peripheral restraining member 50 and the connecting rail 60 having high strength. Furthermore, the square pipe 41 made of an aluminum alloy having a high thermal expansion coefficient and the heat removal block 70 can effectively dissipate decay heat and improve the heat removal performance.

  Furthermore, when the cask is suspended when the fuel assembly is not stored, the load of the cask can be directly supported by the bottom plate 53 via the connecting rail 60 and can be stably carried.

  In this embodiment, in order to absorb the thermal stress generated by the decay heat of the fuel assembly, the coupling mechanism 80 is provided with a fixed portion and a slide portion so that the slide width is δ4 (= 0) <δ3 <. Although δ2 <δ1 (= ∞), when the cask is suspended during storage of the fuel assembly, a large load is applied to the coupling mechanism 80, so that the first to fourth insertion portions 61 to 64 slide due to thermal expansion. Later, the second to fourth fitting portions 24, 25, and 33 are supported by contacting the upper surfaces of the second to fourth fitting portions 62 to 64 so that the load is not applied to the fastening bolt. The first to fourth fitting portions 61 to 64 may be configured to be slidable, for example, as δ4 = δ3 = δ2 = δ1.

13 First fitting portion 21 Upper intermediate plate 22 Lower intermediate plate 24 Second fitting portion 24a Screw hole 25 Third fitting portion 25a Screw hole 33 Fourth fitting portion 33a Screw hole 40 Bundle body 41 Corner Pipe 50 Peripheral restraining member 51 Top plate 52 Intermediate plate 53 Bottom plate 60 Connecting rail 61 First fitting portion 61a Long hole 61b Fastening bolt (fastener)
62 2nd insertion part 62a Long hole 62b Fastening bolt (fastener)
63 3rd insertion part 63a Long hole 63b Fastening bolt (fastener)
64 4th insertion part 64a hole 65b fastening bolt (fastener)
70 Heat removal block 80 Connection mechanism O Bundle body axial direction

Claims (5)

A supporting and fixing device for a cask basket for transporting or storing spent nuclear fuel assemblies,
A bundle in which a plurality of square pipes are arranged with the side surfaces facing each other;
A plurality of constraining plates that are fitted over the outer periphery of the bundle over the entire circumference and arranged at predetermined intervals in the bundle axis direction;
A plurality of connecting rails arranged along the bundle axis direction on the outer periphery of the restraining plate, and connecting all the restraining plates to each other via a connecting mechanism;
Supporting and fixing a cask basket, characterized in that all of the coupling mechanism or all but one restraining plate can be slid in the bundle axial direction within the allowable range of the thermal expansion length of the bundle. apparatus. The coupling mechanism is
Of the fitting parts formed on the restraint plates,
A fitting portion that is formed on a connecting rail and is fitted to allow the fitting portion to slide in the axial direction of the bundle in the range of the thermal expansion length of the square pipe;
The cask basket supporting and fixing device according to claim 1, further comprising: a fastener that slidably connects the fitting portion and the fitting portion within a range of the thermal expansion length. An aluminum alloy heat removal block is arranged between adjacent connecting rails, and the square pipe and the heat removal block are made of aluminum alloy.
The supporting and fixing device for a cask basket according to claim 1 or 2, wherein the restraining plate and the connecting rail are made of steel. The restraint plate is composed of a top plate disposed at the upper end of the bundle, a bottom plate disposed at the lower end of the bundle, and an intermediate plate disposed between the top plate and the bottom plate.
The fitting portion of the connecting rail to which the fitting portion of the top plate is fitted is L-shaped in a side view with the upper end opened, and the connecting rail to which the fitting portions of the bottom plate and the intermediate plate are fitted respectively. The cask basket supporting and fixing device according to claim 1, wherein the fitting portion has a side-viewing angular groove shape. The connection mechanism between the bottom plate and the connection rail is tightly coupled, and the connection mechanism between the intermediate plate and the connection rail is slidable within the range of the thermal expansion length of the square pipe from the bottom frame to the intermediate plate. 5. A cask basket supporting and fixing device according to claim 4,

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