JPH0545492A - Fuel storage rack - Google Patents

Abstract

PURPOSE:To obtain a fuel storage rack of high reliability by increasing the strength of a welded part and by lessening the number of manufacturing processes. CONSTITUTION:A square tube 11 of a fuel storage rack is made of boron-added stainless steel, and a cut part is formed in a plurality of places at intervals in the axial direction in a corner part thereof. By butt-welding a small piece made of stainless steel to the cut part, these square tubes are arranged checkerwise at necessary intervals. In the outermost peripheral part of the rack, a side plate is buttwelded to the cut parts and thereby a plurality of fuel storage cells 16, 17 and 18 are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel storage rack for containing nuclear fuel for a nuclear reactor, and more particularly to a spent fuel storage rack.

[0002]

2. Description of the Related Art Generally, in a nuclear power plant, spent fuel taken out from a nuclear reactor core is temporarily stored until reprocessing, and the storage is used as a spent fuel storage pool (hereinafter referred to as pool). ) Is stored in a spent fuel storage rack (hereinafter referred to as a rack) and cooled and stored. In recent years, various improvements have been made to reduce the interval between stored fuels in order to effectively use the space in the pool. However, in such a rack, in order to maintain the subcriticality in the fuel storage state, interpose a material with a large neutron absorption capacity between the fuels and keep the fuels at intervals even during an earthquake. It is necessary to have sufficient strength so that it can be stored. In order to satisfy such conditions, and because it is easy to assemble, we will combine a pre-formed square tube, and this square tube contains boron with excellent neutron absorption capacity and boron addition with sufficient strength. It is made of stainless steel.

That is, in this type of rack, as shown in FIGS. 5 and 6, a square tube 11 made of stainless steel to which boron is added and an outer plate 14 are vertically arranged on a base 15. ..
The square cylinders 11 are arranged in a zigzag pattern in the front-rear direction and the left-right direction to fix the lower part to the base 15, and the square cylinders on the outside.
The outer plates 14 close the mutual gaps. With this structure, the spent fuel (not shown) is surrounded by the first fuel storage cell 16 formed by only one square tube 11 and the side walls of the four square tubes 11 in the front-rear, left-right direction. A third fuel storage formed by the second fuel storage cell 17 formed and the outer plate 14 surrounded by the second fuel storage cell 17 and the side wall of each of the three square tubes 11 in only one of the front, rear, left, and right directions. cell
It is designed to be housed in each of the 18 (see Fig. 5).

Then, in order to form the fuel storage cells 16, 17, 18 as shown in FIG. 6, the rectangular cylinders 11 are connected by fillet welding via L-shaped connecting members 12. The size of the fuel storage cells 16, 17, and 18 must be such that the spent fuel can be accommodated without fail in consideration of the original manufacturing accuracy of the fuel itself and also the bending and swelling due to neutron irradiation. On the other hand, in order to store as much spent fuel as possible in the pool, there is also a demand to make this size as small as possible, so that the dimensional accuracy of this is quite severe. Therefore, various jigs are used in order to prevent deformation of the rectangular tube 11 due to welding heat input and obtain required accuracy, and the manufacturing is performed with great care.

[0005]

By the way, when the corner portions of the square tube are welded to each other via the conventional connecting member, the strength of the fillet welding is weaker than that of the butt welding. It was necessary to increase the welding length in order to secure it. As a result, there is a possibility that the deformation of the rectangular tube due to welding heat input may increase. Further, in the case of fillet welding, unless the clearance of the welded portion is controlled with a jig with sufficient accuracy, the welding will be apparent and a welding defect is likely to occur. In particular, since boron-added stainless steel has a lower weldability than ordinary stainless steel,
We need to improve the reliability of the weld. For this reason, there is a problem that a large number of manufacturing steps and costs for jigs and tools and equipment are required. Therefore, eliminating such problems and reducing the deformation due to welding heat input to reduce the welding strain correction man-hours, while increasing the strength and efficiency of the welding joint to reduce the absolute amount of welding and reduce the total manufacturing man-hours. Had to plan.

The present invention has been made under such circumstances, and the purpose thereof is to increase the strength of the welded portion,
It is to provide a highly reliable fuel storage rack by reducing the number of manufacturing steps.

[0007]

In order to achieve the above object, according to the present invention, each spent fuel is stored in each of a plurality of fuel storage cells formed by a gap between a plurality of square tubes. In a fuel storage rack that is aligned and held in an upright state, the square tube is made of boron-added stainless steel, and a plurality of cutouts are provided at the corners in the axial direction at a distance in the axial direction. These square tubes are arranged in a checkered pattern at a required interval by butt-welding small pieces made of metal, and the fuel storage cell is formed by butt-welding the side plate to the notch at the outermost peripheral portion of the rack. It is characterized by forming a plurality.

[0008]

In the spent fuel storage rack of the present invention, a plurality of boron-added stainless steel square tubes are arranged in a checkered pattern at a required interval, and the distance between them in the axial direction of the corners of adjacent square tubes is set. The first fuel storage cell is formed by butt-welding the cutouts provided with each other with a cruciform ordinary stainless steel piece. At the same time, 4 in front, back, left and right
A second fuel storage cell is also formed around each side wall of the one square tube. Furthermore, the outer plate (made of boron-added stainless steel or ordinary stainless steel) should be butt-welded directly to the outermost peripheral portion of the rectangular tube, or butt-welded via a T-shaped ordinary stainless steel small piece. Accordingly, only one of the front, rear, left, and right directions is the outer plate, and the third fuel storage cell is surrounded by the outer plate and the respective side walls of the three rectangular tubes. Then, each spent fuel is stored in each fuel storage cell formed in this way,
It can be aligned and held upright. Since the connection of the square tubes is performed by butt welding as described above, the reliability and strength of the welded portion are improved as compared with the conventional fillet welding.

[0009]

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

The structure of the spent fuel storage rack according to the present invention is shown in FIG. 2 on the base 15 as shown in FIGS.
a, a part of the corner of the boron-added stainless steel square cylinder 11 itself as shown in FIG. 2b is cut out, and the corner of the cross-shaped ordinary stainless steel square cylinder 11 itself is cut into this cutout 2. Cut out a part of this, and butt-weld a cross-shaped ordinary stainless steel small piece 1 to this notch 2 and weld the corners of adjacent square cylinders 11 of the square cylinders 11 arranged in a checkerboard pattern. The first fuel storage cell 16 surrounded by one square tube is formed by fixing the square tube 11 at a plurality of positions in a direction and connecting the square tubes 11 upright. A second fuel storage cell is also formed surrounding each side wall of the four rectangular cylinders 11. Further, with respect to the outermost square tube 11, the outer plate 19 is butt-welded and attached to the notch 2 which is formed by cutting out a part of the corner of the square tube 11 itself, so that one of the front and rear or left and right directions is attached. Only the direction is the outer plate 19, and this and the side walls of the three rectangular tubes 11 surround and form the third fuel storage cell 18 (see FIG. 4). The outer plate may be made of boron-added stainless steel or ordinary stainless steel.

Here, in the butt welding of the outer plate 19, instead of providing the protrusion 3 on the outer plate 19 and butt-welding the cutout 2 of the rectangular tube, the notch 2a is provided on the outer plate to form a T-shaped ordinary shape. Square piece of stainless steel small piece 1a
11 and 2 outer plates 14 and 1 butt weld may be used (see FIGS. 2a, 2b and 3). Cross-shaped or T-shaped pieces for connection are readily available by drawing or extruding. In the example of FIG. 1, an 11 × 3 rack is shown, but other combinations such as 11 × 11 will not cause any problem.

When the square tube of the present invention is assembled into a rack, it is manufactured by the following steps (1) to (7). (1)
A square tube is manufactured, and (2) bending of the square tube is corrected, dimensions are measured, and preparation is made for processing the cutout portion 2 for assembly. (3) Next, the cutout portion 2 is processed by centering with a carbon dioxide gas or a YAG laser. (4) The cross-shaped small piece 1 is welded to each axial position at two corners adjacent to each other of the rectangular tube 11 (TIG welding or laser welding. Laser welding has less heat input and less deformation). (5) The outer plate is processed and the notch 2a is processed. (6) A T-shaped piece and, if necessary, a cross-shaped piece are welded to the rectangular cylinder at the outermost peripheral position. (7) To connect and fix the square tube with small pieces on the rack from the outermost side of the rack using a jig. Weld the small piece corresponding to the unwelded notch of the rectangular tube or the small piece corresponding to the outer plate. At this time, the connection with the rack base is performed in parallel.

As described above, in the present invention, the first fuel storage cell 16 is formed, and at the same time, the second fuel storage cell 17 is also surrounded by the side walls of the four rectangular cylinders 11 extending in the front, rear, left and right directions. The outer plate is attached to the outermost peripheral portion of the square tube 11.
A third fuel storage cell 18 is surrounded by 19 and the respective side walls of the three square tubes 11. The spent fuels thus formed are stored in the respective fuel storage cells, and can be aligned and held in an upright state.

In the present invention, the corners of the staggered square cylinders are partially cut away, and the cross-shaped small pieces are butt-welded together. As a result, against the compressive or tensile force in the front-rear and left-right directions of the rack, the force is compressive stress or tensile stress at the weld between the cross-shaped small piece 1 between the square tubes or the outer plate and the T-shaped small piece 1a between the square tubes. Only works, so
In conventional fillet welding, shear stress acts on the weld and structural weakness is improved.

Further, when the outer plate 14 is welded to the outer peripheral rectangular tube 11, if the outer plate is butt welded with the protrusion only in one of the front-back direction and the left-right direction, the other 90 ° direction of the outer plate (left-right direction or Since tensile stress between the rectangular tube 11 and the outer plate (in the front-rear direction) and the compressive stress causes shear stress at the welded portion, the butt welding via the T-shaped small piece is stronger in terms of strength.

To form this fuel storage cell, FIG.
As shown in Fig. 2, the notches that are provided at a distance in the axial direction of the corners of the adjacent rectangular tubes are butt-welded with the cross-shaped ordinary stainless steel small pieces, so that the rectangular tubes 11 are connected to each other by L
The welding heat input is smaller than the case where fillet welding is performed via the connecting member of the mold, the strength of the welded portion is higher than that of fillet welding, and the welding joint efficiency is increased. Therefore, the welding amount required for strength is reduced, and the welding deformation amount of the rectangular tube 11 itself is inevitably reduced. Therefore, it is possible to reduce the manufacturing costs of various jigs and tools for obtaining the required manufacturing accuracy, and the man-hours for attaching and detaching them and the man-hours for welding.

Particularly when the outer plate 14 is made of boron-added stainless steel, it is necessary to provide a protrusion for welding with a square tube and directly weld the protrusion to the notch of the square tube to increase the cut-off portion of the member. However, since the yield of use of expensive boron-added stainless steel plate is deteriorated, it is more convenient to use the above-mentioned T-shaped small piece.

Further, by butt-welding the outer plates, the outer dimensions at the time of rack assembly can be shortened by the thickness of the outer plates (about 1 cm) as compared with the conventional fillet welding of the outer plates. In addition, if the outer plate is made of boron-added stainless steel, the periphery of each fuel storage cell is equally surrounded by the neutron absorbing plate, and any fuel storage cell has a subcritical property problem even if the fuel approaches from the outside of the rack. There is no.

[0019]

As described above, in the spent fuel storage rack according to the present invention, a plurality of square tubes made of boron-added stainless steel are arranged in a checkered pattern at required intervals, and adjacent square tubes are formed. The first fuel storage cell is formed by butt-welding the cross-shaped notches provided at a distance in the axial direction with each other by butt-welding small cross-shaped pieces made of ordinary stainless steel. At the same time, the second fuel storage cell is also surrounded by the side walls of the four rectangular cylinders in the front-rear, left-right direction. In addition, the outer plate is butt-welded to the outermost peripheral portion of the square tube with a small piece of ordinary T-shaped stainless steel, so that only one of the front, rear, left, and right directions is the outer plate. A third fuel storage cell is formed surrounding each side wall at.

The spent fuel is stored in each of the fuel storage cells thus formed, and can be aligned and held in an upright state. By adopting such a structure, the storage density of the spent fuel can be increased, and the structure of the welded portion has high strength and reliability, the manufacturing man-hours can be reduced, and a highly reliable fuel storage rack can be obtained. ..

[Brief description of drawings]

FIG. 1 is a plan view of a fuel storage rack according to an embodiment of the present invention.

2 (a) is a perspective view showing a main part of FIG. 1, and FIG. 2 (b) is an enlarged cross-sectional view of part A of FIG.

3 is a side view of the fuel storage rack shown in FIG. 1. FIG.

FIG. 4 is a side view showing another embodiment of the fuel storage rack shown in FIG.

FIG. 5 is a plan view showing a conventional example of a fuel storage rack.

FIG. 6 is an enlarged plan view showing a method of connecting adjacent rectangular cylinders in a conventional example.

[Explanation of symbols]

1 ... Cross-shaped small piece for connecting between square tubes 1a ... T-shaped small piece for connecting square tube / outer plate 2 ... Square tube cutout 2a ... Outer plate cutout 3 ... Outer plate projection 11 ... Square tube 12 ... L-shaped member for connection 14 , 19 ... Outer side plate 15 ... Rack base 16 ... First fuel storage cell 17 ... Second fuel storage cell 18 ... Third fuel storage cell

Claims (2)

[Claims] 1. A fuel storage rack in which respective fuels are respectively housed in a plurality of fuel storage cells formed by a plurality of square tubes and gaps between the square tubes and aligned and held in an upright state, wherein the square tubes are Made of boron-added stainless steel,
A plurality of cutouts are formed in the corners at a distance in the axial direction, and a small piece of stainless steel is butt-welded to the cutouts to join the fuel storage cells. Fuel storage rack to do. 2. The fuel storage rack according to claim 2, wherein
A plurality of square tubes made of boron-added stainless steel are arranged in a checkered pattern at required intervals, and the notches provided at a distance in the axial direction of the corners of the adjacent square tubes form a regular cross shape. First by butt-welding small pieces made of stainless steel
Fuel storage cells are formed, and second fuel storage cells are formed on the side walls of the four rectangular cylinders in the front-rear, left-right direction, and the outer plate is made of T-shaped stainless steel on the outermost peripheral portion of the rectangular cylinders. By butt-welding the small pieces, only one of the front, rear, left, and right directions is the outer plate and the third fuel storage cell is formed by this and the side wall of each of the three square tubes. The fuel storage rack is characterized in that each spent fuel is stored in the fuel storage cell of, and can be aligned and held upright.