JPH0670679B2 - Support grid - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a support grid for a fuel assembly for a nuclear reactor.

[Conventional technology]

A fuel assembly to be loaded into a nuclear reactor is formed by arranging a number of long cylindrical fuel rods in which a large number of short cylindrical pellets are sealed so as to be parallel to each other at regular intervals. . In this case, a support grid is used as a means for holding the fuel rods in such a positional relationship.

As shown in FIG. 17, this support grid is formed by assembling a large number of straps 1 made of rectangular thin plates in a grid pattern vertically and horizontally.

Of the inner surfaces of each cell 2 of such a support grid, two adjacent surfaces farther from the center of the grid have elasticity toward the center of the cell 2 as shown in FIGS. 18 and 19. The spoiler 3 which it has is formed, and the dimple 4 is formed toward the center of the cell 2 on the surface opposite to the protruding surface of this spoiler 3.

When a fuel rod is inserted into each cell 2 of such a support grid,
The fuel rod is pressed against the dimple 4 by the elastic force of the spring 3, and the fuel rod is regulated by the dimple 4 at a predetermined position.
In this case, it is supported at the center of the cell 2.

Therefore, by disposing the support grids at several positions in the longitudinal direction of the fuel rod, it is possible to construct a fuel assembly in which a large number of fuel rods are supported in parallel at regular intervals.

[Problems to be Solved by the Invention]

By the way, the spring 3 of the conventional supporting grid is
As shown in the figure, it is an inelastic leaf spring bent in a mountain shape, and this inelastic spring has a wider control range for obtaining a target spring force with respect to the amount of deflection than an elastic spring. Although it has an advantage, it has a large hysteresis, and it cannot be denied that the holding force may change if it is used over a long period of time.

The present invention has been made in view of the above circumstances, and an object thereof is to reliably hold a fuel rod,
A stable holding force can be secured from the start of use to the end of use of the fuel rods, and the assembly and manufacture of the fuel assembly can be easily and efficiently performed, and the quality can be improved. To provide a support grid.

[Means for Solving the Problems]

In order to achieve the above object, the present invention provides a spring,
A flat elastic spring portion which is formed integrally with the strap and is flush with the strap, and an inelastic spring portion which is continuous with the elastic spring portion and is bent in the thickness direction. It is configured.

[Action]

In the support grid of the present invention, by the non-elastic spring portion,
A wide control range of the spring force with respect to the amount of deflection is secured, and the elastic spring portion suppresses hysteresis of the inelastic spring portion.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a perspective view showing an example of a strap. In this strap, a large number of slits 11 are formed in a strip-shaped thin plate 10 from one end to a central portion at regular intervals, and between these slits 11, 11. The springs 12 are formed so as to project to one side of the strip-shaped thin plate 10, and the slots 13 are formed on both sides of these springs 12.
The dimples 14 are formed at both ends of the strip so as to project to the other side of the thin strip 10.

The spring 12 has an inelastic spring portion 12a formed in a middle portion thereof, which is bent in the thickness direction and protrudes in a mountain shape as shown in FIGS. 2 and 3, and the inelastic spring portion 12a. And an elastic spring portion 12b which is continuous with both ends of the strip-shaped thin plate 10 and which is formed wider toward the end and has the same planar shape as the strip-shaped thin plate 10.

The strap configured as described above is assembled to the supporting grid by brazing or welding as in the conventional case, and the fuel rod is inserted by the spring force of the spring 12 by inserting the fuel rod into the lattice space of the supporting grid. It is pressed against the dimples 14 and supported at a predetermined position.

In this case, the spring characteristic of the spring 12 is a combination of the characteristics of the inelastic spring and the elastic spring, as shown in FIGS. 4 and 5. That is, FIG. 4 shows an inelastic spring,
The case where the apparent spring constant is made larger than the elastic spring constant is shown, and FIG. 5 shows an example in which the elastic spring constant is made larger than the apparent spring constant of the inelastic spring. Therefore, the fuel rod is characterized by the characteristics of the inelastic spring portion.
It is held by a spring force that does not depend on the amount of displacement,
If the flexure becomes excessive, the spring force increases, so the holding force does not decrease.

FIG. 6 shows a second embodiment of the present invention. In this embodiment, a spring 15 is formed instead of the spring 12 of the first embodiment.

This spring 15 has a non-elastic spring portion 15 protruding in a mountain shape.
a, and at both ends of the non-elastic spring portion 15a, an opening 15c is formed which is wider toward the end and has a substantially triangular shape. As a result, the non-elastic spring portion 15a has substantially the same width and Elastic spring part 15 which is in the same plane as the thin strip 10
It consists of b and. This opening 15c has an advantage that a jig can be inserted at the time of assembling the support lattice and at the time of assembling the fuel assembly.

In the spring 15 configured as described above, the inelastic spring portion 15a and the elastic spring portion 15b are responsible for the displacement, and the spring force with respect to the initial displacement amount is the first.
It has properties similar to those of the example, and therefore has extremely small hysteresis.

Furthermore, FIG. 7 shows a third embodiment of the present invention.
The spring 16 of this embodiment includes an inelastic spring portion 16a and an elastic spring portion 16b narrower than the inelastic spring portion 16a.

In the spring 16, when the elastic spring portion 16b having a narrow width receives the initial displacement, the spring characteristic becomes linear, and therefore the hysteresis is small. Further, when the displacement proceeds to some extent, the inelastic spring portion 16a also takes charge of the displacement, so that the spring force that does not depend on the displacement amount is held, and the spring force does not decrease even if excessive deflection occurs. Furthermore, by selecting the shape of the inelastic spring, and by properly combining the amount of deflection that the inelastic spring bears with the amount of deflection that the elastic spring bears, if the amount of deflection is further increased, the spring force can be increased again. it can. Also,
By eliminating the rib portion 17 shown in FIG. 6, the width ratio between the inelastic spring portion 16a and the elastic spring portion 16b can be increased.

Specific examinations of the spring characteristic curves for the above three examples are shown in FIG. 9, FIG. 12 and FIG.

Of these, FIG. 9 is a spring characteristic diagram obtained by using the example of the spring 12 shown in FIG. In this spring 12, the inelastic spring portion 12a has a narrow width, and the stress applied to this portion is large. Therefore, the initial displacement is preferentially received by this inelastic spring portion 12a, resulting in a non-linear curve. . Even if the displacement proceeds to some extent, this non-linear characteristic is maintained, and the spring characteristic in this region holds the spring force that does not depend on the displacement amount. Further, when the displacement further proceeds, the elastic spring portion 12b also takes charge of the displacement, and linearity appears as the spring characteristic, and the spring force increases with the displacement. Therefore, the spring force does not decrease even if the deflection becomes excessive. Here, since the starting point and the area width of each area depend on the length and width (shape) of the elastic spring portion 12b and the inelastic spring portion 12a, and have a linear portion, the hysteresis is the inelastic spring. Very small compared to.

FIG. 12 is a spring characteristic diagram obtained by using the example of the spring 15 shown in FIGS. 10 and 11. In this spring 15, since the non-elastic spring portion 15a and the elastic spring 15b have the same width, the stress received by each portion is the same, and the displacement is evenly shared by both portions. As a result, essentially, the characteristics of the inelastic spring are maintained, but the spring force with respect to the initial amount of displacement has a relatively linear characteristic, and therefore the hysteresis is extremely small.

FIG. 14 is a spring characteristic diagram obtained by using the example of the spring 16 shown in FIG. In this spring 16,
Since the elastic spring portion 16b is narrow and the stress applied to this portion is large, the initial displacement is preferentially received by the elastic spring portion 16b, and the spring characteristic is linear. Then, when the displacement progresses to some extent, the inelastic spring portion 16a also takes charge of the displacement, and as a spring characteristic, it holds a spring force that does not depend on the displacement amount. Next, when the displacement further proceeds, the linear change is again exhibited, and therefore the spring force does not decrease even if excessive deflection occurs. The starting point and width of each region depend on the length and width (shape) of the inelastic spring portion 16a and the elastic spring portion 16b, and since this spring 16 has a linear portion, hysteresis is small.

In addition, in each of the above-mentioned embodiments, the description has been made by using the springs 12, 15, 16 which are supported at two points (both ends).
As shown in the figure, a one-point supporting (cantilever) spring 20 composed of an inelastic spring portion 20a and an elastic spring portion 20b may be used.

〔The invention's effect〕

As described above, according to the present invention, the spring in the support grid is formed of a flat plate-shaped elastic spring portion which is configured to be integral with the strap and flush with the strap, and which is continuous with the elastic spring portion. Since it is configured to include an inelastic spring portion that is bent in the thickness direction, the inelastic spring portion ensures a wide control range of the spring force with respect to the amount of deflection, and the elastic spring portion provides inelasticity. By suppressing the hysteresis of the spring portion, the fuel rod can be reliably held, and a stable holding force can be secured from the start of use of the fuel rod to the end of use. ,
Further, by artificially bending the elastic spring portion, the spring force applied to the fuel rod when the fuel assembly is assembled can be temporarily reduced, and workability and workability can be improved. Furthermore, the spring characteristics can be easily controlled by adjusting the spring width, spring plate thickness, spring length, and spring shape of the elastic spring portion and the inelastic spring portion.

[Brief description of drawings]

1 to 5 show a first embodiment of the present invention. FIG. 1 is a perspective view of a strap, FIG. 2 is a side view showing an example of a spring portion protruding to one side, and FIG. The figure is a side view showing an example of a spring portion protruding to both sides, and FIG. 4 is an explanatory view showing the spring characteristics of an inelastic spring when the apparent spring constant is made larger than the elastic spring constant, FIG. Is an explanatory view showing the spring characteristics when the elastic spring constant is made larger than the apparent spring constant of the inelastic spring, FIG. 6 is a perspective view showing the second embodiment of the present invention, and FIG. 7 is the present invention. A perspective view showing a third embodiment, FIGS. 8 to 14 are concrete demonstrations of the first, second and third embodiments, and FIG. 8 shows an example of a spring of the first embodiment. Explanatory drawing, FIG. 9 is a spring characteristic diagram of the spring of FIG. 8, and FIG. 10 shows an example of the spring of the second embodiment. FIG. 11 is an explanatory view showing another example of the spring of the second embodiment, FIG. 12 is a spring characteristic diagram of the springs of FIGS. 10 and 11, and FIG. 13 is of the third embodiment. FIG. 14 is an explanatory view showing an example of a spring, FIG. 14 is a spring characteristic diagram of the spring of FIG. 13, FIG. 15 is a side view of a spring protruding to one side with cantilever support, and FIG. 16 is both with cantilever support. Fig. 17 is a side view of the spring protruding to the side of Fig. 17, Fig. 17 is a perspective view of the support grid portion, and Fig. 18 is a plan view of a conventional support grid.
FIG. 19 is a perspective view of the same, and FIG. 20 is a side view of a conventional spring. 10 …… Thin strip, 12,15,16,20 …… Spring, 12a, 15a, 16a, 20a …… Inelastic spring part, 12b, 15b, 16b, 20b …… Elastic spring part, 13 …… Slot.

Claims (1)

[Claims] 1. A plurality of thin strip-shaped straps are crossed with each other to form a large number of lattice spaces, and a part of the straps forming these lattice spaces is projected to one side or both sides to form a spring. In a support grid formed integrally with the spring and punching out both ends of the spring to form slots, the spring is a flat plate formed integrally with the strap and flush with the strap. Elastic spring part of
A support grid, comprising: an inelastic spring portion that is continuous with the elastic portion and is bent in the thickness direction.