JPH06331771A - Spacer for fuel assembly - Google Patents

Abstract

PURPOSE:To obtain a spacer having low pressure loss and excellent in limit output characteristics and workability by forming the fuel rod holding part while bending a lead spring inward along the upper and lower end faces of a round cell. CONSTITUTION:A leaf spring 40 is assembled, back to back, with another leaf spring 40 or a leaf spring having other shape the leaf spring 40 embraces two short round cells 32 with upper and lower linear parts 41 being disposed in a coolant channel defined by four short round cells 32 in order to regulate the lateral movement. The linear part 41 is provided, at the upper and lower ends thereof, with horizontally stretching parts having bent parts being fitted to the short round cell 32 such that the projection area is shaded by the short cell 32. Consequently, the end face of the cell 32 functions to reduce the projection area of the leaf spring 40 and to regulate the vertical movement of the leaf spring 40. The part projecting to the inside of the cell 32 forms the fuel rod holding part. In the assemblage of spacer, the cells 32 arranged laterally in a row are welded each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spacer for maintaining a fuel rod interval of a nuclear fuel assembly for a nuclear reactor.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional boiling water reactor fuel assembly. Both ends of the fuel rods 1 arranged in an 8 × 8 lattice are held by an upper tie plate 3 and a lower tie plate 4. The fuel rods 1 are about 4 m long and the spacing of the fuel rods 1 between the upper tie plate 3 and the lower tie plate 4 is maintained by seven spacers 2.

The structure of the spacer 2 is shown in FIG. 3, and the inside of the square surrounded by the band 12 is divided into 4 × 4 by the dividers 7 and 8.
= Make 16 small squares. This small square is divided into four equal parts by the bars 19 and 20 to form a smaller square into which one fuel rod 1 can be inserted.

A lantern box 9 and a lantern spring 10 are arranged at the intersections of the bars 19 and 20, and
The fuel rod 1 is held by the S bend 11 provided in 8 or the dimple 13 provided inside the band 12.

Such a square grid spacer 2 has a low limit output of the fuel rod 1 due to uneven flow of the coolant, and a high burnup fuel assembly intended for use in an improved boiling water reactor. Not suitable for the body. Therefore, a round cell type spacer as disclosed in JP-A-3-35640 has been proposed. The round cell type spacer 21 is shown in FIGS. 4, 5, 6, 7 and 8.
The structure of The round cell type spacer 21 is formed by arranging cylindrical round cells 22 in 8 × 8 and enclosing the periphery with a band 12, and the contact between the round cells 22 and the round cells 22 and the band 12 are arranged.
Welded contacts. As shown in FIG. 5, the round cell 22 is provided with notches 23 at the upper end and the lower end, and the end portion of the notch 23 is bent inward to form the stopper 2
Form four four. Further, a C-shaped notch 26 for holding the loop spring 25 as shown in FIG. 6 is provided on the side surface of the round cell 22 as shown in FIG.

[0006] The C-shaped notch 26 of one round cell 22 is abutted with the C-shaped notch 26 of another circular cell 22 which is turned upside down and looped by two C-shaped notches 26 as shown in FIG. The spring 25 is sandwiched and the loop spring 25 is held so as to restrain the lateral movement. The pair of round cells 22 shown in FIG. 8 are efficiently arranged to form the spacer 21 as shown in FIG. The fuel rod 1 and the water rod 27 are held on one side of the two stoppers 24 and the loop spring 25.
Similar to the conventional square lattice spacer 2, the band 12 is provided with a bathtub 28 for keeping a distance from a channel box (not shown) and a flow tab 28 for deflecting the coolant flow near the channel box in one direction of the fuel rod. is there.

[0007]

Round cell type spacer 21
It has been confirmed that the fuel cell assembly has improved limit output characteristics as compared with the conventional square lattice spacer 2, but the pressure loss increases.

As for the material of the round cell type spacer 21, only the loop spring 25 is an Inconel material, and other than this, a zirconium based alloy (Zircaloy 2, Zircaloy 4) having a small neutron absorption cross section is used. JP-A-4-8758 describes that the zirconium-based alloy is deteriorated in plastic workability and corrosion resistance depending on the working process. Even if the zirconium-based alloy round cell 22 is manufactured by a desirable manufacturing process, it is not desirable to process the stopper 24 and the C-shaped notch 26.

An object of the present invention is to provide a spacer having good limiting output characteristics, small pressure loss, and good workability.

[0010]

[Means for Solving the Problems] A leaf spring is held by a coolant passage formed by four round cells and upper and lower end surfaces of the round cell without forming a stopper or a C-shaped cut in the round cell. A part of the leaf spring along the upper and lower end surfaces of the round cell is bent inward of the round cell to form a holding portion for the fuel rod, and the holding portions of the four leaf springs hold the fuel rod. Further, the length of the round cell is shortened by the width of the leaf spring along the upper and lower end surfaces of the round cell.

[0011]

The thickness of the round cell is about 0.5 mm, while the thickness of the spring is about 0.3 mm. If the stopper that bends part of the round cell inward is eliminated, the projected area will decrease by that amount, but the projected area of the leaf spring will be larger than the projected area of the conventional loop spring. Is almost the same as However, the pressure loss of the spacer is reduced by the amount that the length of the round cell is shortened by about 1/3. Round cell is 1/3
Even if it becomes shorter, the limit output characteristic is better than that of the square lattice spacer.

Since the workability of Inconel of the spring is better than that of the zirconium-based alloy of the round cell, it is advantageous in working to make the shape of the leaf spring somewhat complicated without forming a stopper or a C-shaped cut in the round cell. Is.

[0013]

EXAMPLE An example of the present invention will be described below.

FIG. 1 is a plan view of the spacer 30. As the fuel assembly, one having a single large-diameter water rod 31 at the center was used. The leaf springs are shown thicker than they actually are for the sake of clarity, but there are five types of leaf springs 40, 50, 6
0, 70, 80 are used. The spacer 30 is symmetrical with respect to the large-diameter water rod 31 in the vertical direction and the horizontal direction, but is not symmetrical in the diagonal direction. The leaf spring 4 is shown in FIG.
0 was shown. Normally, the leaf spring 40 is assembled back-to-back with another leaf spring 40 as shown in FIG. 10 or another leaf spring. The leaf spring 40 has a shape that holds two short round cells 32, and the upper and lower straight line portions 41 are in the coolant passage formed by the four short round cells 32, and the left and right movements are restricted. There are horizontal springs that extend to the left and right above and below the straight line portion 41, and the bending portion 42 has a short round cell 32.
The shadow area of the short round cell 32 is a projected area. Therefore, the projected area of the leaf spring 40 is reduced and the vertical movement of the leaf spring 40 is restricted by the end face of the short round cell. The portion protruding inside the short round cell 32 is the holding portion 43 of the fuel rod 1. When it is attempted to hold one fuel rod 1 by the four holding portions 43, it is impossible only by combining the leaf springs 40. Therefore, the leaf spring 50, the leaf spring 60, and the leaf spring 70 are required.

The leaf spring 50 shown in FIG. 11 has a straight line portion 5
There are two 1s and a leaf spring 54 that pushes the fuel rod between the two short round cells 32. The leaf spring 54 is made separately, and the leaf spring 5
Weld to zero. The leaf spring 50 is provided between the upper short circular cell 32 and the band 12 and the lower short circular cell 3 in FIG.
Used alone between 2 and band 12. Between the second and third short circular cells 32 from the top of FIG.
Between the third and third short round cells 32, they are used back-to-back as shown in FIG. Further, between the third and fourth short round cells 32 from the top and between the third and fourth short round cells 32 from the bottom, the other leaf springs 80 are used back to back. The functions of the bending portion 52 and the holding portion 53 are the same as those of the leaf spring 40.

A leaf spring 6 used in the center of the vertical direction of FIG.
0 is shown in FIG. Two leaf springs 60 are used back to back, and the functions of the straight portion 61 and the holding portion 63 are the leaf springs 4.
Same as 0,50.

FIG. 14 shows a leaf spring 70 which is in contact with the band 12 at the right and left central portions of FIG. The leaf spring 70 has three straight line portions 71 and does not have a curved portion like the leaf spring 60. The functions of the linear portion 71 and the holding portion 73 are the same as those of the leaf springs 40 and 50 described above. Leaf spring 80 shown in FIG.
Is a leaf spring 40 to which a water rod holding spring 85 is added.

The procedure for assembling the spacer 30 is to connect the short round cells 32 in a row in FIG. 1 by welding. The conventional round cell has a stopper and a C-shaped cut, and the direction at the time of assembly is determined, but the short round cell 32 has no directivity.

Next, a predetermined leaf spring is placed at a predetermined position between the band 12 and the short round cells 32 in the first row in order from the top or the bottom, and the row of short round cells 32 is pressed against the band 12 to make the band. 12 and the short round cell 32 are welded. FIG. 16 shows the case where the height of the band 12 is set to be the same as the height of the leaf spring. In such a case, a notch 33 whose bottom matches the end face of the short round cell 32 is provided at a position in contact with the short round cell 32.
If the bands are provided above and below the band 12, welding becomes easy. If the height of the band 12 is made the same as the length of the short round cell 32, the notch 33 becomes unnecessary, and the pressure loss is reduced by the length of the band 12.

A predetermined leaf spring is placed at a predetermined position between the short round cells 32 in the first row and the short round cells 32 in the second row, and the short round cells 32 in the first and second rows are pressed against each other. And the band 12 are welded together. Thereafter, the cells are assembled one by one in this manner, and the welding is performed on the short round cells 32 and the band 12 in the eighth row.

As another assembling procedure, a predetermined leaf spring is placed at a predetermined position between the rows of the short round cells 32 welded laterally in advance, and the rows are finally connected. Band 1 is an assembly of × 8 short round cells 32 and leaf springs.
There is a method in which the short round cell 32 and the band 12 are welded together by putting them in the No. 2 cell.

[0022]

According to the present invention, the limit output characteristic is good,
A spacer with low pressure loss and good workability can be provided.

[Brief description of drawings]

FIG. 1 is a plan view of a spacer according to an embodiment of the present invention.

FIG. 2 is a side view of a boiling water reactor fuel assembly.

FIG. 3 is a plan view of a conventional square lattice type spacer.

FIG. 4 is a plan view of a conventional round cell type spacer.

FIG. 5 is an explanatory view of a conventional round cell type spacer.

FIG. 6 is a perspective view of a loop spring of a conventional round cell type spacer.

FIG. 7 is an explanatory diagram of a round cell C-shaped cut of a conventional round cell type spacer.

FIG. 8 is a plan view showing an attached state of a loop spring of a conventional round cell type spacer.

FIG. 9 is a perspective view showing the shape of a leaf spring according to an embodiment of the present invention.

FIG. 10 is a perspective view showing a mounted state of the leaf spring of the present invention.

FIG. 11 is a perspective view showing the shape of the leaf spring of the second embodiment of the present invention.

FIG. 12 is a perspective view showing a mounted state of a leaf spring according to a second embodiment of the invention.

FIG. 13 is a perspective view showing the shape of another leaf spring of the third embodiment of the present invention.

FIG. 14 is a perspective view showing the shape of a leaf spring according to a fourth embodiment of the present invention.

FIG. 15 is a perspective view showing the shape of a leaf spring according to a fifth embodiment of the present invention.

FIG. 16 is a perspective view showing an assembled state of the band and the short round cell of the present invention.

[Explanation of Codes] 1 ... Fuel rod, 2, 21, 30 ... Spacer, 3 ... Upper tie plate, 4 ... Lower tie plate, 12 ... Band, 2
2, 32 ... Round cell, 24 ... Stopper, 25 ... Loop spring, 40, 50, 60, 70, 80 ... Leaf spring.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nagakichi Takuji 7-2-1, Omika-cho, Hitachi-shi, Ibaraki Hitachi Energy Research Institute, Ltd.

Claims (1)

[Claims] 1. A spacer comprising a round cell for penetrating a plurality of fuel rods, a spring arranged for each round cell to press and hold the fuel rod, a band for bundling the round cells, and the like. Without providing a push-out protrusion to regulate the movement of the
The fuel rod is formed by protruding the upper and lower end portions of the spring material, which penetrates the coolant passage formed between the four round cells, along the upper and lower end surfaces of the round cell, and bending a part thereof into a protrusion shape. A spacer for a fuel assembly, wherein the spacer is pressed.