JPH02114197A - Spacer in fuel assembly - Google Patents

Abstract

PURPOSE:To contrive the prevention of fretting corrosion by forming an angular space of a space fuel rod inserting lattice space in the center part and shaping projections for limiting the deformation of a plurality of springs supporting a water tube in the inner face of the angular space of a pair of vertical and horizontal lattice plates. CONSTITUTION:When a fuel assembly is assembled, spacers 10 are formed in line at several stages and fuel rods 1 are inserted in each lattice space 14a while thick angular water tubes 2 are inserted in an angular space 14b of the center. Two-way arc-shaped projections of clip-like springs 16 attached to the all sides surrounding the spaces 14a and other two-way angle resilient pieces abut on the side face of each fuel rods 1. Further, angle resilient pieces of the springs 16 attached to the center part of each vertical and horizontal lattice plates 12, 13 making the spaces 14 abut on the all sides of the water tube 2 to support resiliently. When large lateral load is applied to the fuel assembly by an earthquake and the like in the constitution, the angle resilient pieces of the springs 16 are immediately deformed, but they abut on a plurality of projections 15, the water tube 2 is supported by the projections 15 in a constant condition without the permanent deformation of the springs 16 and out of contact with the fuel rod 1.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a spacer in a fuel assembly for a boiling water nuclear reactor, particularly in a fuel assembly designed to use a large diameter water tube.

(Prior Art) A fuel assembly for a boiling water reactor (hereinafter referred to as BWR) generally consists of a predetermined number of fuel rods 1 and one or two rods arranged in the center, as shown in Fig. 4. Fuel rods and water pipes 2 of approximately the same diameter are arranged in a 7x7 or 8x8 square arrangement, and their upper and lower ends are attached to upper and lower tie plates 3 and 4 via rod-shaped end plugs,
They are held in the middle by several stages of lattice-shaped spacers 5, and the outside is covered with a rectangular cylindrical channel box 8. Recently, in order to extract as much thermal energy as possible from the fuel, While increasing the enrichment of the fuel, the water pipes are made thicker to increase the volume of unboiled water in the fuel assembly, thereby increasing the reactivity of the fuel.

In other words, as shown in Figure 5, 70 or so fuel rods 1 are arranged in a 9x9
The cross-sectional area corresponding to the direct product occupied by 3 x 3 or 2 x 2 fuel rods (-side 2 to
A rectangular water pipe 2 with a wall thickness of 1 to 2 m) is arranged,
These fuel rods 1 and water pipes 2 are divided into a lattice space 7& in which the inside of the outer frame 5a of the spacer 5 arranged in several stages in the axial direction is divided by a predetermined number of vertical and horizontal lattice plates 5b and 56, respectively; Square spaces 7bK each having a width of 2 rows and 2 columns are inserted into the 3 rows and 3 columns of the 9 lattice spaces 7a formed in the center, and are divided by vertical and horizontal lattice plates 5b and 5e for fuel rods. In the center of the four surrounding sides of each grid space 7a,
As shown in FIG. 6, a narrow plate is bent, and a plurality of arch-shaped protrusions 6b are provided on the negative side of the plate, and clip-shaped springs b with chevron-shaped elastic pieces 6& formed on the other side are attached to lattice plates 5b and 5c, respectively.
For the fuel rod 1, the angle-shaped elastic piece 6a is brought into contact with the fuel rod 1, and the arc-shaped projection 6 is attached to the other rod.
b are brought into contact with each other and supported, while the water pipe 2 is elastically supported with three or two chevron-shaped elastic pieces 6a brought into contact with each other on the west side, thereby reducing the axial elongation of the fuel rods 1 and water pipes 2. guaranteed.

(Problem to be solved by the invention) The clip-shaped springs attached to the vertical and horizontal lattice plates of the spacer of the fuel assembly are usually made of a strong alloy such as Inconel, and the springs are large and thick. If it is formed into a solid material, a supporting material that is unlikely to undergo permanent deformation can be obtained, but if such a strong spring is made, it will strongly press down on the water pipe and will inhibit the free elongation of the water pipe in the axial direction. As a result, this suppresses the elongation of the fuel rod and causes it to bend.Inconel is a Ni-based alloy, and Nl
This is because Co naturally contains Co, and when the fuel is in use, this Co becomes 66Co, which has extremely strong radioactivity, and is leached into the coolant, potentially contaminating the reactor with radioactivity. Because it is desirable to limit the use of Inconel as much as possible, springs with a plate width of 2 cm or less, a wall thickness of 0.5 cm or less, and a holding force of about 2 h are currently used.

By the way, when an earthquake occurs and an acceleration of about 2 G is applied to the fuel assembly, as shown in FIG. The fuel assembly is deformed due to the
At this time, the fuel rods 1 with low rigidity easily follow the deformation, but the water tubes 2 with high rigidity do not deform, and the elastic pieces 6 & of the springs 6 that support the water tubes 2 are crushed, causing the springs 6 was permanently deformed and could no longer hold the water tube 2 with the appropriate force υ, and fretting corrosion (friction corrosion) occurred due to vibration between the fuel rod 1 and there was a risk of damaging the fuel rod. .

SUMMARY OF THE INVENTION An object of the present invention is to provide a spacer that properly supports water pipes and does not damage fuel rods even if a large lateral load is applied to a fuel assembly due to an earthquake or the like.

(Means for Solving the Problems) Based on the above object, the present invention divides the inside of the outer frame into a large number of lattice spaces into which fuel rods are inserted using a predetermined number of vertical and horizontal lattice plates, and A rectangular space for water pipes with an area corresponding to 3 rows and 3 columns or 2 rows and 2 columns of the above-mentioned lattice space is formed in the section, and a clip-shaped spring is attached to the center of each of the four sides surrounding each lattice space. As a spacer for a fuel assembly, the side surfaces of water pipes to be inserted into are supported by a plurality of elastic pieces of clip-like springs, the square shapes of the two vertical lattice plates and the horizontal lattice plates forming the square spaces for the water pipes are used. The inner surface of the space is characterized in that protrusions are formed on both sides of the clip-shaped springs attached to each grid plate to limit the deformation of the springs to within the elastic deformation.

(Example) Fig. 1 shows a spacer 1 made of Zircaloy-4 according to the present invention.
Although the plane of 0 is shown, the inside of the rectangular cylindrical outer frame 11 is divided into 9
It is divided into lattice spaces 14 and 14, into which some 70 fuel rods 1 arranged in a square arrangement of 9x9 are to be inserted, and in the center there is a space corresponding to 3x3 of the lattice space 141 for fuel rods. A rectangular space 14b for water pipes is formed, and is divided by vertical and horizontal lattice plates 12.13, and clip-shaped springs 16 are installed at the center of each of the four sides of each lattice space 14m for nine fuel rods, respectively. These clip-like springs 16 are formed by bending a narrow plate made of Inconel alloy (width: about 2 mm, wall thickness: about 0.5 as). As shown in Figure 3, there are multiple arcuate protrusions 1 on one side.
6b, and a chevron-shaped elastic piece 16m is provided on the other side (however,
As for the spring fixed to the outer frame, only the chevron-shaped elastic pieces are provided), and for the fuel*IK fitted into the grid space 14&, the arc-shaped protrusion 16b and the other chevron-shaped elastic pieces 16 are provided.
The structure is different from the one described above in that the water pipe 2 inserted into the central rectangular space 14b is supported by a plurality of chevron-shaped elastic pieces 16 and all of its west side. No.

By the way, in this invention, the square space 14 for the woodwind in the center is
As shown in FIGS. 2 and 3, on the inner surface of the central part of the two vertical lattice plates 12 and horizontal lattice plates 13 forming the lattice plate 12 and 13, there are installed lattice plates 12 and 13 at regular intervals, respectively. Along both sides of the plurality of clip-shaped springs 16, a semi-ellipse protrudes inward at approximately half the height of the chevron-shaped elastic pieces 16m of the spring (the height that limits the deformation of the chevron-shaped elastic pieces to the range of elastic deformation). A shaped protrusion 15 (width: about 3 mm, length: about 15 mm) is provided by stamping, welding, or other means.

Therefore, when assembling the fuel assembly, the spacer 1
0 are arranged in several stages and the fuel rods 1 are inserted into each of the lattice spaces 14&, and the thick rectangular water pipes 2 as described above are inserted into the square space 14bK at the center. The arcuate protrusion 16b of the clip-shaped spring 16 attached to the four sides surrounding the fuel rod 14& and the chevron-shaped elastic piece 16a of the other clip come into contact with the side surface of each fuel rod 1 to support it, and the rectangular space 14b A plurality of chevron-shaped elastic pieces 16a of clip-shaped springs 16 are attached to the center portions of two vertical and horizontal lattice plates 12 and 13, respectively, which make up the water pipe 2, and come into contact with the four sides of the water pipe 2 to elastically support it.

When a large lateral load is applied to the fuel assembly due to an earthquake and the assembly is deformed, that force acts between the water pipe 2 and the spacer 10, and the force acts on the water pipe 2. The elastic pieces 16b of the springs 16 on the vertical or horizontal lattice plates supporting the lattice plates are immediately deformed, but in the process of deformation, the water pipes 2 υ, spring 16 that does not come into contact with the protrusion 15
is not permanently deformed, and the water tube 2 is supported in a constant state by the protrusion 15 and does not come into contact with the fuel rod 1.

Further, when the external force disappears, the water pipe 2 separates from the protrusion 15 and is supported only by the spring 16 again.

Note that in the above example, the central rectangular space 14b is the lattice space 1.
41, but this may be as wide as 2 rows and 2 columns. Also, the shape of the elastic piece 16m of the clip-shaped spring 16 and the protrusion 16b, and the protrusion The shape of 15 is not limited to the one shown in the drawings, but may be any other shape.

(Effects of the Invention) As described above, in this invention, a rectangular space with a width of 3 rows and 3 columns or 2 rows and 2 columns of the lattice space for insertion of fuel rods is formed in the center, and the lattice space for insertion of fuel rods is formed in the center. Each clip is used as a spacer for a fuel assembly in which a large diameter water pipe is supported by a plurality of elastic pieces of clip-shaped springs, and each clip is attached to the inner surface of the square space of each pair of vertical and horizontal lattice plates forming the square space. Since protrusions are formed on both sides of the spring to limit the deformation of the spring to within elastic deformation, the clip-like spring that supports the water pipe will not be permanently deformed even if a large lateral load is applied to the fuel assembly due to an earthquake, etc. As a result, the water tubes can be supported in a constant state without touching the fuel rods, and corrosion of the fuel rods is prevented and there is no risk of breakage.

[Brief explanation of drawings]

FIG. 1 is a plan view of an embodiment of the invention. FIG. 2A is an enlarged plan view of the section taken along line A-A in FIG. The same mouth is the same < A-Am section front view. FIG. 3 is a sectional view taken along line B-B in FIG. 1. FIG. 4 is a partially cutaway perspective view of a normal fuel assembly. Figure 5 shows a conventional spacer for a fuel assembly using a large diameter water pipe. FIG. 6 is a sectional view taken along line CC in FIG. 5. FIG. 7 is an explanatory diagram showing a state in which the fuel assembly is deformed by a lateral load. In the figure 1...Fuel rods 5.10...Spacers 5 circles 12...Vertical lattice plates 7a, 14a...Grate spaces 15...Protrusions 6a, 16a...Chevron-shaped elastic pieces 2... - Water pipes 5a, 11--Outer frames 5e, 13--Horizontal lattice plates 7b, 14b--Square spaces 6.16--Clip springs 6b, 16b--Arc-shaped protrusions Patent applicant Nuclear fuel Industrial Co., Ltd.

Claims (1)

[Claims] The inside of the outer frame is divided into a number of lattice spaces into which fuel rods are inserted using a predetermined number of vertical and horizontal lattice plates, and in the center there are 3 rows and 3 columns or 2 rows and 2 columns of the above lattice spaces. A rectangular space for water pipes of a wide area is formed, and clip-shaped springs are attached to the center of each of the four sides surrounding each lattice space, and the sides of the water pipe that is inserted into the square space are supported by the elastic pieces of the plurality of clip-shaped springs. In the spacer, on the inner surfaces of the rectangular spaces of the two vertical lattice plates and the horizontal lattice plates forming the prismatic space for water pipes, there are springs on both sides of the clip-shaped springs attached to each lattice plate. A spacer for a fuel assembly, characterized in that each spacer is formed with a protrusion that limits deformation to within elastic deformation.