JPH02216088A - Fuel assembly spacer - Google Patents

Abstract

PURPOSE:To soften impact force from the outside and resiliently support water tubes by forming embossed pieces on each side of a plate frame surrounding an angular space in which a large-diameter water tube is inserted and attaching grip-like holding springs. CONSTITUTION:The inside of an outer frame 1 is divided into lattice cells 4 in which fuel rods n are inserted by lattice plates 2, 3 of vertically and laterally specified number, in the center part, a water tube R inserted angular space 5 equivalent to 3X3 rows or 2X2 rows of the cell 4 are formed and further grip-like holding springs 6 are attached to the center part of four sides of each cell 4. Embossed pieces 7 projected in a space 5 at the position corresponding to each adjacent cell 4 along an upper edge and a lower edge in the center part of lattice plates 2, 3 forming the space 5 are formed and springs 6 are attached so as to sandwich the lattice plates 2, 3 and the upper and lower pieces 7. By the above constitution, since the fuel rods and a water tube R are resiliently supported and the pieces 7 are neared to the side face of the water tube R, impact force can be softened even when lateral load is received.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a spacer for a fuel assembly in which a large diameter water tube is used in the fuel assembly.

(Conventional technology) In recent years, in order to reduce the operating costs of nuclear power plants in light water reactors, there has been a demand for long-term cycle operation of the reactor and more economical combustion of the fuel (uranium) in the fuel assembly. One way to meet this demand is to increase the enrichment of the fuel so as to extract as much thermal energy as possible from the fuel without changing the size of the assembly itself, and to increase the thickness of the water pipes to reduce the amount of waste in the assembly. There is a known method in which the volume of boiling water is increased to increase the reactivity of the fuel.

The outline of the system is as shown in Fig. 4, A7, with over 70 fuel rods arranged in 9 rows and 9 columns, and 3 in the center.
Rectangular water pipes R having a cross-sectional area corresponding to the area occupied by fuel rods n in 3 rows and columns or 2 rows and 2 columns are arranged, and the fuel rods n and water pipes R are arranged in several stages in the axial direction. The interior of the outer frame S1 of the spacer S is covered with vertical and horizontal lattice plates S2 and S3.
The fuel rods n are inserted into the lattice cells C divided by It is attached to the center of the four sides and is elastically held by an Inconel alloy clip-shaped retaining spring e having a chevron-shaped elastic piece e1 on one side and a square or arc-shaped protrusion e2 on the other side, as shown in Fig. 4C. In addition, the water pipe R is supported on its four sides by three or two similar clip-shaped springs e, and the upper and lower ends of the fuel rod n and the water pipe R are attached to the upper and lower tie plates LI+LZ. , a tunnel box B is fitted on the outside to form a fuel assembly, a predetermined number of which are placed upright on the seat F1 of the core structure F, and during the operation of the reactor, the channel box B is placed on the seat F1. A coolant is sent into the inside of the water tube R and the inside of the channel box B through the orifice F2, and heat is taken out to the outside.

(Problem to be solved by the invention) By the way, using a large diameter water pipe as described above is useful for increasing the burnup of the fuel, but the large diameter water pipe is not suitable for fuel rods or conventional pipes of the same diameter. Since the rigidity is greater than that of the water pipe, if the gap with the surrounding grid plate is not appropriate, the impact force against the grid plate during an earthquake will be quite large, causing permanent deformation of the retaining spring and making the water pipe unstable. Also, since the large diameter water tube is a non-heating element and the capacity of the coolant passing through the inside is larger than that of conventional ones, there is a liquid phase on the outer circumferential surface. The coolant exists in the form of a film, and this phenomenon causes the coolant to be biased toward the non-heating element, which is unfavorable in terms of cooling efficiency for the fuel. By optimizing the spacing of the spacer lattice plates that surround this, it is possible to properly hold large diameter water pipes by alleviating the impact force in the event of an earthquake, etc., while increasing its strength, and diffusing the liquid film to improve cooling efficiency. The purpose is to provide a spacer that allows

(Means for Solving the Problems) Based on the above object, the present invention divides the inside of the outer frame into a predetermined number of fuel rod insertion cells vertically and horizontally, and has three rows and three columns of cells in the center. Or, as a spacer in which a rectangular space corresponding to the width of 2 rows and 2 columns and surrounded by frame plates is provided, and a rectangular large-diameter water pipe is inserted and arranged in the space, each of the frame plates surrounding the rectangular space is Embossed pieces that are parallel to the edges and protrude into the space are formed on each side, and clip-shaped retaining springs are attached to the formed parts of these extruded pieces, so that the water pipe is elastically supported by these springs. It is characterized by

(Embodiment) Figures 1A, 9B and 1C show an embodiment of a spacer S made of Zircaloy-4 according to the present invention. The lattice plate 2.3 divides into lattice cells 4 into which 70 or more fuel rods arranged in 9 rows and 9 columns are to be inserted, and in the center there are 3× lattice cells 4 for inserting fuel rods. A rectangular space 5 for fitting the water pipe R is formed, which is equivalent to the width of three spaces, and
In the center of each of the four sides of the lattice cell 4 divided by the horizontal lattice plates 2.3, there are narrow plates made of Inconel alloy (
(width approx. 2 mm, wall thickness approx. 0.5 mm), fold the opening in Figure 1,
As shown in C, a clip-shaped retaining spring 6 has a chevron-shaped elastic piece 6a on one side and a plurality of square or arc-shaped protrusions 6b on the other side (however, only the chevron-shaped elastic piece is the spring attached to the outer frame. The fuel rod n inserted into the lattice cell 4 is supported by the angle-shaped elastic pieces 6a on three sides and the protrusions 6b on the other three sides, and is inserted into the square space 5 in the center. The water pipe R is supported on all four sides by a plurality of chevron-shaped elastic pieces 6a, respectively. However, this configuration is no different from the one described above. By the way, in the above-mentioned example of this invention, each of the two vertical lattice plates 2 and the horizontal lattice plates 3 forming the square space 5 at the center have an upper edge and a lower edge as shown in FIG. A protruding piece 7 protruding into the space 5 is formed at a position corresponding to each adjacent lattice cell 4 along the lattice plate, and a clip-shaped retaining spring 6 provided at this portion is attached to the lattice plate main body as shown in FIG. It is attached so as to sandwich the upper and lower embossing pieces 7. Therefore, when assembling the aggregate, the spacer S
are arranged in several stages, and a fuel rod n is placed in each grid cell 4.
At the same time, if a large-diameter rectangular water pipe R as described above is inserted into the central rectangular space 5, each cell 4 will have an angle-shaped elastic piece 6a of a retaining spring 6 attached to its two sides, and other parts. The protrusions 6b of the springs on the two sides come into contact with the circumferential surface of the fuel rod n to support it, while in the square space 5, a plurality of spring protrusions are placed in the central part of the vertical and horizontal lattice plates 2.3 surrounding this. The chevron-shaped elastic piece 6a of the holding spring 6 that has been taken out comes into contact with the side surface of the hole in the water pipe R to elastically support it, and the embossed piece 7 provided on each lattice plate 2, 3 contacts the side surface of the water pipe R. close to. and,
When a lateral load is applied to the fuel assembly due to an earthquake, the assembly is deformed, and the force acts between the water pipe R and the spacer S, the elastic piece 6a of the retaining spring 6 is
is immediately deformed, and the stamped pieces 7 on the vertical or horizontal lattice plate come into contact with the water pipe R to support it in a constant state. In this case, the punched piece 7 is close to the water pipe R and the gap between them is smaller than the gap between the two and the regular grid plate, so the spring 6
The deformation remains within the elastic deformation range, and the impact force is also reduced to a small extent, so that the spring and spacer are not damaged.

Furthermore, even if a liquid film of the coolant is formed along the surface of the water tube R during operation of the furnace, the punched pieces 7 of the lattice plates 2 and 3 surrounding the water tube R will be exposed to the surface of the water tube at the spacer S portion. Because they are close together, it is possible to separate and disperse the flow of the liquid film and direct it toward the fuel rod.

Figure 2 A 2 is a vertical lattice plate 2 and a horizontal lattice plate 3 that form a rectangular space 5 in the center. Partitioning represents a variation of a longer series spanning multiple grid cells 4, but its functionality is no different from the example described above.

On the other hand, FIG. 3 shows the insertion cell 14 of the fuel rod with Zircaloy-4
In this example, the outer frame 11 has a cylindrical frame with a constant height as shown in C in the same figure, and there are protrusions at multiple locations on the top and bottom of the inner surface. 1
2a and a circular tube element 12 having a leaf spring 12b attached to a part of the side circumference so that the center thereof protrudes inward.
are arranged in 9 rows and 9 columns and welded to each other in series, and in the center there are approximately 3 rows and 3 columns (or 2 rows and 2 columns) of circular tube elements 12.
A substantially rectangular space 15 corresponding to an area of
A rectangular inner frame 13 inscribed in is provided, and what is its contact area? 8 is connected.

On each side of the inner frame 13, a space 1 is provided at a position between the circular tube elements 12 arranged in parallel along the upper edge and the lower edge, as shown in the opening of the figure.
A clip-shaped retaining spring 16 is attached to the formed portion of the punched piece 17 so as to sandwich the inner frame body and the punched piece. It is designed to support the water pipe R.

In this way, the stamped pieces 17 of the inner frame 13 can separate and disperse the flow of the liquid film of coolant generated on the surface of the water pipe R, and in the event of an earthquake, the stamped pieces 17 stop receiving the water pipe R and absorb the impact force. can be alleviated.

In the example shown in FIG. 3, the punched pieces 17 are not individual, but may be a series of long pieces as shown in FIG.

In addition, the punched pieces may not be in a state directly along the edges of the lattice plate or inner frame as shown in the figure, but may be in a state parallel to the edges, and the clip-shaped retaining spring is not limited to the one shown in the figure, but may have other shapes. It can also be from.

(Effects of the Invention) As described above, according to the present invention, the inside of the outer frame is divided into a predetermined number of fuel rod insertion cells vertically and horizontally, and the central part has 3 rows and 3 columns or 2 rows and 2 columns of cells. A rectangular space corresponding to the width of Since we have formed protruding pieces that are parallel to the edges and protrude into the space, the rigidity of the water pipe insertion part is improved, and in the event of an earthquake, the spacing between the wood pipe and the surrounding lattice plate can be optimized. By this, the support can be stopped immediately by the punched piece close to the water pipe and the impact force can be reduced to a small extent, and by attaching the retaining spring to this part, the deformation of the spring can be stopped within the elastic deformation. , damage to the spacer and retaining spring is prevented;
Moreover, the flow of a liquid film of coolant generated on the surface of the water tube during operation of the reactor can be dispersed to the fuel rod side, which has the advantage that cooling efficiency can be improved.

[Brief explanation of the drawing]

FIG. 1 is a plan view of an embodiment of the invention. The opening in the figure is a perspective view of the two sides of the center. FIG. 1C is a sectional view taken along line XX-Q in FIG. FIG. 2A is a perspective view of the center two sides of the modified example. The opening in the figure is a plan view of the central part. FIG. 3A is a partial plan view of yet another modification. The figure shows a perspective view of the center and sides of the opening. FIG. 3C is a perspective view of the circular tube element. FIG. 4A is a schematic side view of the fuel assembly. The figure is a plan view of the conventional spacer taken along the Y-Y line. C in the same figure is a side cross section taken along the Z-X line four times.

Claims (1)

[Claims] The inside of the outer frame is divided vertically and horizontally into a predetermined number of fuel rod insertion cells, and in the center there is a square space corresponding to the area of 3 rows and 3 columns or 2 rows and 2 columns of the cells and surrounded by a frame plate. In the spacer in which a rectangular large-diameter water pipe is inserted and arranged in the space, a stamped piece is formed on each side of the frame plate surrounding the rectangular space and extends parallel to the edge and projects into the space, and A spacer for a fuel assembly, characterized in that clip-shaped holding springs are attached to the forming portions of the stamped pieces, and the water tubes are elastically supported by the springs.