JP3088679B2 - Spacer for fuel assembly - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spacer for a fuel assembly of a light water reactor, particularly a boiling water reactor.

[0002]

2. Description of the Related Art Generally, in a fuel assembly for a light water reactor, a number of elongated fuel rods are bundled, and the top of each fuel rod is held by an upper tie plate and the lower end is held by a lower tie plate. The intermediate portion of each fuel rod is held by a plurality of spacers, and the fuel rods are held and fixed in a state where they are separated from each other.

FIG. 5 is a longitudinal sectional view of the general fuel assembly. The lower end of fuel rods 1 arranged substantially in a grid is supported by a lower tie plate 2, and each fuel rod 2 Is held by an upper tie plate 3. In the fuel assembly, a plurality of spacers 4 are provided at intermediate positions thereof, and a predetermined interval is maintained between the fuel rods 1.

[0004] In the light water reactor, the coolant normally flows upward from below the fuel assembly arranged vertically, and the fuel assembly flows during the nuclear reaction by the coolant. Cooling of the fuel rods throughout the body takes place. Therefore, in the fuel assembly, it is necessary to allow the coolant to pass around the fuel rods 1 as desired, and the nuclear fuel rods 1 are held at a predetermined distance from each other by the spacers 4 to operate the nuclear reactor. The fuel rods are prevented from bending or vibrating inside.

As the spacer, a lattice type or a round cell type is conventionally used. FIG. 6 is a view showing the configuration of the above-mentioned round cell type spacer. A space 5 for inserting a water rod is provided at the center, and a large number of cylindrical cells 6 are provided on the outer periphery thereof with their axes parallel to each other. The hand 7 is mounted on the outer periphery of the aggregate of the cells 6. The adjacent cells and the cell and the band are connected to each other by welding to form one spacer 4. By inserting the fuel rod 1 into each cell 6, the fuel rod can be held at a predetermined position. it can.

[0006]

Each of the above-mentioned cells is usually formed by cutting a thin-walled tube made of a zirconium alloy into a predetermined length to form a tube, as shown in FIGS. 7 (a) and 7 (b). The fuel rod supporting projections 6a, 6a are formed at upper and lower ends of the cylindrical cell 6 symmetrically with respect to the diameter, respectively, and the fuel rod supporting projections 6a, 6a are formed. A C-shaped notch 6b is formed on the side surface opposite to the surface provided, and a spring holding piece 6c is formed.

Therefore, a spring 8 (FIGS. 6 (a) and 6 (b)) is inserted into the notch 6b of the cell 6 to be supported by a spring holding piece 6c, and then the second cell 6 is rotated. A spring 8 supported on the spring holding piece 6 of the first cell by the spring holding piece 6c of the cell.
To form a cell pair as shown in FIG. And a plurality of cells manufactured in this way
A pair and a band are assembled, and these cells or between the cell and the band are welded by laser or TIG welding.

However, since the above cell is cylindrical,
As shown in FIG. 9, the cells are in contact at one point. Since welding is performed at this position, there is little welding molten metal and there is a gap due to circumferential contact, and the molten metal melts down from the gap. There is also a problem that the shape is not necessarily suitable for good welding, and that the welding strength cannot be increased due to a single point contact on the circumference.

For this reason, it has been proposed to use a deformed tubular cell as shown in FIGS. 10 (a) and 10 (b) in order to increase the contact portion of each cell.

However, in the case of using such a modified tube, the cost for producing the modified tube increases,
In addition, the resistance to the flow of the cooling water increases, and there is a problem that it is not always advantageous from the viewpoint of the pressure loss when viewed from the low pressure loss type for the cooling water of the current design.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to increase the welding strength and obtain an economical fuel assembly spacer.

[0012]

According to the present invention, a large number of cylindrical cells are arranged so that their axes are parallel to each other, assembled together by a band, and a fuel rod is inserted into each of the cells. By doing so, in the fuel assembly spacer in which the fuel rods are held apart from each other, the cylindrical cell has a cylindrical hole slightly larger than the diameter of the cell and has a 90 ° angle above the hole. By inserting into a mold having grooves at four locations in the gap, and inserting and molding a punch having a conical projection projecting at 90 ° intervals corresponding to the grooves of the mold from the open end side of the cell, At least one end of the cylindrical cell has a flat surface portion perpendicular to the diameter of the cell at a position where the adjacent cells or the cell and the band are in contact with each other on the outer peripheral surface portion of the cylindrical cell, and the adjacent cell in the flat surface portion Between and cells And the band is welded.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an enlarged view of the spacer of the present invention as viewed from the tube end, and FIG. 2 is a perspective view of the cell. A spacer is formed on the outer periphery of one end of the cell 6 by the cell 6. A flat surface portion 10 that is orthogonal to the diameter of the cell is formed at a position where the cell and the band are adjacent to each other. That is, in the cell, the flat surface portion 10 is provided over a predetermined width at four positions, that is, a side surface portion on which the spring holding piece 6c is provided, a side surface portion facing the spring holding piece 6c, and left and right side surface portions orthogonal to the side surface portion. The dimension S between the opposing flat surface portions 10 substantially matches the outer diameter dimension R of the cell.

When a spacer is formed using such a cell, as shown in FIG. 3, the flat surface portion 10 comes into contact with the flat surface portion or band of the adjacent cell. Therefore, welding strength can be increased by connecting the flat surface portions that are in contact with each other by welding.

FIG. 4 is a diagram showing a schematic configuration of the cell manufacturing apparatus. An opening 12 into which a cell tube can be inserted is formed at the center of a die 11. Are concave portions 1 corresponding to the flat surface portion at four positions every 90 °.
3 are formed. On the other hand, the punch 14 cooperating with the die 11 is provided with a tapered portion 15 whose tip portion is smaller than the inner diameter of the cell 6 and gradually becomes larger. A convex portion 16 is formed for each degree.

In manufacturing the cell, a cell tube (outer diameter R = 16 mm) made of a zirconium alloy is cut into a predetermined length, and this is inserted into the opening 12 of the die 11.
Thereafter, the punch 14 is lowered to press only the tube end of the cell. In this manner, the flat surface portion 10 is formed at the end of the cell 6 by the concave portion 13 of the die 11 and the convex portion 16 of the punch 14.
Are formed.

The size of the concave portion 13 of the die 11 and the size of the convex portion 16 of the punch 14 can be appropriately selected from the hardness of the cell tube used, the wall thickness and the diameter of the tube, and the like. Is 16 mm, the interval S between the flat surface portions opposing each other is 16 mm, and the width dimension of the flat surface portions is 2 mm to 8 mm.
mm, particularly preferably 2 mm to 5.5 mm. That is, when the width of the flat surface portion is 2 mm or less, the effect of the flat surface is not obtained. When the width is 8 mm or more, the protrusion from the outer diameter of the cell 6 increases to 1 mm, which is not preferable because the resistance of the cooling water is large. Further, the relationship between the interval S between the flat surface portions and the outer diameter R of the cell 6 is as follows.
S is R or more and (R + 2) or less, preferably R or more and (R +
1) The following is assumed. That is, when a conventional cell diameter is used, S = R.

The conventional design can be satisfied by reducing the outer diameter R of the conventional cell 6 by at most 2 mm and projecting the flat surface portion so that the interval S between the flat surface portions 10 is 16 mm. In this case, it is necessary to form flat surfaces on both ends of the cell 6.

After the formation of the flat surface portion 10, the notch 6b and the protrusion 6a are formed by using a known method with the flat surface portion 10 as a reference.
Is processed.

In the above embodiment, the flat surface portion 10 is provided only on the outer periphery of one end of the cell, but may be provided on the outer periphery of both ends. In particular, in a nuclear reactor, the cooling water flows from the lower side to the upper side, and higher welding strength is required at the lower welding position. It is preferable to form the flat surface portion 10 on the outer peripheral portion of the end portion on the tie plate side.

Although the flat surface portion 10 is formed first, the flat portion may be formed at the final stage after the conventional cell is formed.

[0022]

As described above, according to the present invention, the diameter of the above-mentioned cell is set at the position where at least one end of the cylindrical cell comes into contact with the adjacent cells or the cell and the band. Is formed, and the adjacent cells and between the cell and the band are welded on the flat surface portion, so that the welding surface can be enlarged and the welding strength can be increased. In addition, the manufacturing cost does not increase as in the case of a deformed tube, and only a press step is added. Therefore, the increase in the manufacturing cost is slight, and further, the conventional cell manufacturing apparatus can be processed with almost no change. .

[Brief description of the drawings]

FIG. 1 is an enlarged view of a cell of a spacer according to the present invention as viewed from a tube end.

FIG. 2 is a perspective view of a cell in the spacer of the present invention.

FIG. 3 is an explanatory view showing a welded portion of a cell according to the present invention.

FIG. 4 is a diagram showing an example of a cell processing apparatus according to the present invention.

FIG. 5 is a vertical side view of a general fuel assembly.

FIG. 6A is a plan view of a conventional spacer, and FIG. 6B is a partial cross-sectional side view of the spacer.

FIG. 7A is a view of the conventional cell viewed from a tube end, and FIG.
Is a perspective view thereof.

FIG. 8 is a plan view showing a connection portion between cells in a conventional spacer.

FIG. 9 is an enlarged explanatory view of a welded portion between cells in a conventional spacer.

FIGS. 10A and 10B are diagrams showing cells formed by deformed tubes, respectively.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fuel rod 4 Spacer 6 Cell 7 Band 8 Spring 10 Flat surface part 11 Die 13 Concave part 14 Punch 15 Tapered part 16 Convex part

Claims (3)

(57) [Claims] 1. A plurality of cylindrical cells are arranged so that their axes are parallel to each other, are assembled integrally by a band, and fuel rods are inserted into each of the cells, whereby each fuel rod is connected. In the spacer for a fuel assembly which is held apart from each other, the above-mentioned cylindrical cell is connected directly to the cell.
It has a cylindrical hole that is slightly larger than the diameter.
° Place the mold in a mold with grooves at four locations and open the cell.
Conical shape from the mouth end side, 90 ° interval corresponding to the groove of the mold
To insert and mold a punch with a convex part that protrudes with
More, the at least one end portion outer peripheral surface of the tubular cell, the position of contact between each other, or cell and a band adjacent to one another to form a flat surface portion perpendicular to the diameter of the cell, adjacent in its flat surface portion A spacer for a fuel assembly, wherein a space between cells and between a cell and a band are welded. 2. The fuel assembly spacer according to claim 1, wherein the flat surface portion is provided at an end portion on the lower tie plate side when the spacer in each cell is assembled into the fuel assembly. . 3. The fuel assembly spacer according to claim 1, wherein a dimension between opposed flat surface portions of each cell is substantially equal to an outer diameter of the cell.