JPH055517Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a spacer support device for keeping a large number of fuel rods at regular intervals in a fuel assembly for a boiling water nuclear reactor.

(Prior art) In a fuel assembly for a boiling water reactor, two fuel rods 1 and one or two water rods 2 are normally arranged in 8 rows and 8 columns, as shown in Fig. 5. The upper and lower ends are fitted and supported by upper and lower tie plates 3a and 3b, and spacers 4 are disposed in several stages in the middle to maintain a constant horizontal spacing.

As for the spacer 4, the required number of dividers and bars are made to intersect vertically and horizontally to form a lattice shape as before, and the dividers are provided with S-shaped bent portions and are formed at the intersections of the bars. In the case where a paper towel-shaped spring assembly is provided to support the fuel rods and water rods, the bends in each grid and the spring assembly occupy a large area, which restricts the flow of coolant. In addition, since the flow of coolant is disturbed at the intersections of dividers and bars, making it impossible to improve the output, recently, as shown in FIG. A part of the tubular elements 5 is bulged inward to form an arc-shaped fixing part 5a, and a vertical slit is provided on the opposite wall surface, and a predetermined number of these tubular elements 5 are arranged in a square with the slits facing each other. A diamond-shaped loop-shaped spring body 5b is fitted therein to connect each tube element 5 vertically and horizontally, and the arc-shaped fixing portion 5a and spring body 5b support the fuel rod 1 and water rod 2.
The tubular element 5 for one water rod 2 is provided with a cut 5c as shown in FIG.
Pass the tab 2a attached to the water rod 2 through the tab 2a, then rotate the water rod 2 to remove the tab 2a.
A so-called ring element type device in which the spacer 4 is supported has been proposed in Japanese Patent Laid-Open No. 59-65287.

(Problem that the invention aims to solve) Incidentally, in recent years, attempts have been made to increase the internal volume of water rods and make them rectangular in cross section, with the aim of increasing the burnup of fuel rods and flattening the axial power distribution. However, in the case of a water rod with a large internal volume and a rectangular cross section, it is not possible to use a means of inserting and rotating the spacer as in the conventional device described above (this also applies to the lattice type spacer), and the rod After incorporating into the spacer,
The tab is welded to a predetermined position, but this method has poor workability and can lead to welding errors.

Therefore, the present invention utilizes the advantages of the element type spacer, improves the burnup of fuel, makes the axial distribution uniform, and provides a spacer support device that allows easy attachment of tabs.

(Means for Solving the Problems) Based on the above objective, this invention requires a spacer that holds a large number of elongated fuel rods arranged in a vertical direction at regular intervals as a spacer support device in a fuel assembly. In the case where several circular or rectangular tube elements are formed adjacent to each other in the left and right front and back, a rectangular water rod having a larger cross-sectional area than the tube element is inserted into the center of the spacer, and at least one corner of the water rod is inserted. On the outside of the corner, a pair of upper and lower tabs is provided at a predetermined interval in the axial direction,
In the space formed by the corner of the water rod where the tab is provided and the tubular element of the spacer surrounding this corner, a vertical recess is provided in the opposite part of the tab, and a cut tongue piece is provided at the upper and lower ends thereof to be bent toward the water rod side. The present invention is characterized in that a holding tube is provided, and its notched tongue pieces are engaged with the tabs to support the spacer.

(Example) Fig. 1 is a plan view showing an embodiment of this invention, and 14 is a spacer, which is a circular tube made of a predetermined number of zirconium alloys and nickel alloys arranged squarely in the left and right front and back. It is composed of an element 15 and a band body 17 made of the same material surrounding the element 15.

By the way, in this invention, a rectangular water rod 12 made of disconium alloy or stainless steel and having a length corresponding to about twice or more the diameter of the tubular element 15 is inserted into the center of the spacer 14. On the outside of one diagonal corner of the water rod 12, there are vertically spaced holes slightly larger than the height of the tubular element 15, that is, the height of the spacer 14, as shown in FIG. While the pairs of tabs 13 are respectively attached, when viewed from a plane as shown in FIG. As shown in FIG. 3B, the tubular element 15 has an arc-shaped vertical recess 16a in the part facing the tab 13, and a cut tongue side 16b is formed at the upper and lower ends of the recess 16a. A small-diameter holding tube 16 is provided, a part of its outer surface is welded to the outer surface of the three tube elements 15, and cut tongue pieces 16b at the upper and lower ends of the vertical recess 16a are bent toward the water rod side. The spacers 14 at each stage are held between pairs of upper and lower tabs 13 on the water rod 12 via the upper and lower cutting tongues 16b.

However, during assembly, the water rod 12 is inserted into the central cavity of the spacer 14 with the tab 13 aligned with the vertical recess 16a of the holding tube 16, and the paired tabs 13 are positioned above and below the tube element 15, and then In this step, the cut tongue pieces 16b at the upper and lower ends of the recess of the holding tube 16 are bent toward the water rod 12 using a jig. FIG. 2 shows its planar state.

Note that the tabs 13 of the water rod 12 are not limited to one diagonal corner as shown in FIG. 1, but may be provided at one corner or all corners.

FIG. 4 shows the tubular element 15 of the spacer 12.
This shows an example of changing the shape to an octagon.

(Effects of the invention) As described above, in this invention, the spacer that holds a large number of fuel rods at regular intervals is made up of a series of circular, square, etc. tubular elements, and the central part of the spacer is A water rod with a large square cross section is inserted, and a pair of upper and lower tabs are provided at regular intervals in the axial direction on the outside of at least one corner of the water rod, and this is connected to the corner of the water rod having the tab. In the space formed by the surrounding tubular element, a holding tube is disposed, which has a vertical recess in the portion facing the tab and has notched tongues bent toward the waterrod side at its upper and lower ends. Since the spacer is held by locking the cut tongue piece to the tab, it is not only possible to prevent the flow of coolant from being restricted or disturbed, but also to reduce the amount of moderator material retained by the water rod. It is possible to increase the burn-up of the fuel and flatten the power distribution in the axial direction.Furthermore, there is no need to attach a tab to the water rod after assembling the spacer, which simplifies the work and reduces welding mistakes. There is no risk of it happening.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an embodiment of this invention. FIG. 2 is an enlarged plan view of the chain line portion in FIG. FIG. 3A is a sectional view taken along the line XX in FIG. 2. FIG. 3B is a perspective view of the holding tube. FIG. 4 is a plan view of a part of the modified example. Fifth
The figure is a cross-sectional view of the fuel assembly. FIG. 6A is a plan view of a half part of a known element type spacer. Figure B is a side view of the spacer support portion. In the figure, 1... Fuel rod, 12... Water rod, 13... Tab, 14... Spacer, 15...
Tube element, 16... holding tube, 16a... vertical recess,
16b...Incised tongue piece.

Claims (1)

[Scope of utility model registration request] In a spacer 14 that holds a large number of elongated fuel rods 1 arranged in parallel in the vertical direction at regular intervals, a required number of circular or square tube elements 15 are formed adjacent to each other in the left and right front and back. A rectangular water rod 12 having a larger cross-sectional area than the tubular element 15 is inserted through the water rod 1.
A pair of upper and lower tabs 13 are provided at a predetermined interval in the axial direction on the outside of at least one corner of the water rod 12, and the corner of the water rod 12 where the tab 13 is provided and the tube body of the spacer 14 surrounding this corner. In the space formed by the element 15, a holding tube 16 is provided with a vertical recess 16a in the opposite part of the tab 13, and provided with cut tongues 16b bent toward the water rod side at the upper and lower ends thereof.
is arranged, and the cut tongue piece 16b is attached to the tab 13.
A support device for a spacer in a fuel assembly, which supports a spacer 14 by being engaged with the spacer.