JPS595991A - Device for retaining interval between fuel assembly - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel assembly spacing device, and more particularly to a fuel assembly spacing device.
The present invention relates to an improvement in a fuel assembly spacing device that elastically maintains the space between each channel box of a fuel assembly for a boiling water nuclear reactor.

Figure 1 shows the basic structure of a fuel assembly for a conventional (boiling water type) nuclear reactor.

A fuel assembly 1 includes a plurality of regularly arranged fuel rods 2.
an upper tie plate 4 and a lower tie plate 5 supporting the fuel rods 2 at their lower ends, and a channel surrounding the fuel rods 2; It is composed of box 6 and the like.

Further, a channel fastener 7 and a channel spacer 8 are attached to the fuel assembly 1 to maintain a constant spacing between the fuel assemblies 1 and to secure an insertion passage for the control rods.

In the reactor core, the fuel assemblies 1 are arranged in place of one of the control rods 10 in the two-part grid plate 9, as shown in FIG. The channel fasteners 7 are arranged at opposing positions to maintain a constant distance between the fuel assemblies 1, 1. The channel fastener 7 supports the fuel assembly 1 with elastic force and absorbs changes in the length and width directions of the fuel assembly 1 due to continuous vibration and thermal expansion during reactor operation. Furthermore, the channel fastener 7 is designed to elastically support the fuel assembly 1 and to reduce damage to the fuel assembly 1 as much as possible even in the event of instantaneous vibrations during an earthquake.

As shown in FIGS. 3 and 4, the channel fastener 7 is composed of a leaf spring 7a, a leaf spring support 71], and both of these members 7a, 71], an upper tie plate post, etc., and a fuel assembly. The force that elastically supports 1 utilizes the repulsive force based on the elastic deflection of the leaf spring 7a.

The structure and function of the conventional channel fastener 7 installed in the fuel assembly 1 are as described above, but the amount of deflection of this channel fastener 7 was studied taking into account the relationship with other reactor internals. If we add this, we have the following problems: In other words, the tolerances imposed on the fuel assembly 1 and furthermore the tolerances imposed on other reactor internals naturally affect the amount of deflection of the leaf spring 7b, which is a component of the channel fastener 7. Yes, but 17 above
If the amount of deflection of the leaf spring 7a is extremely small due to the large influence of tolerances, the predetermined elastic force cannot be obtained by the leaf spring 7a. Note that this problem is caused by the leaf spring 7
This can be solved by increasing the height of the leaf spring 7a in the direction of deflection, but according to this, the stress generated in the leaf spring 7a becomes higher than necessary even in the case of the nominal size, and the amount of deflection of the leaf spring 7a due to vibration etc. If this becomes large, a new problem arises in which the stress generated in the leaf spring 7a exceeds the yield stress and breaks.

The present invention has been made in consideration of the following two points, and its purpose is to provide a fuel assembly with excellent safety that can increase the spacing force between each fuel assembly. It is intended to provide a spacing device.

The present invention provides a fuel assembly spacing device in which a channel fastener is attached to a corner of a channel box in which a plurality of fuel rods are loaded to elastically maintain space between adjacent channel boxes. The leaf spring support that forms part of the above channel fastener includes:
This channel fastener is characterized by being provided with a leaf spring abutting part located below the load position of the leaf spring, which is another constituent part of the channel fastener, and which shares the reaction force of the leaf spring.

Hereinafter, the present invention will be explained based on the conventional example shown in FIGS. 4 and 5, as well as an embodiment shown in FIGS. 6 to 8.

In FIG. 4 showing the mounting structure of the conventional channel fastener, the symbol Lt indicates the distance from the lower end of the leaf spring 7a to the load center position.

5 is a characteristic diagram of the leaf spring of the conventional channel fastener 7 shown in FIG. (obtained by elasticity calculation), curve A
is the stress that occurs near the load, curve B is the stress that occurs at the fixed part of the leaf spring, curve I (is the spring constant, and σ0 is the stress that occurs in the leaf spring 7
It corresponds to the maximum stress generated in the leaf spring 7a when the distance Lt from the lower end of a to the load center position is the nominal base, and I(o indicates the spring constant of the leaf spring 7a at the base.However, The position corresponding to the distance L from the lower end of the leaf spring 7a to the load center position is:
It is indicated by the symbol P in FIG. As is clear from FIG. 5, in order to reduce the stress of the leaf spring 7a and increase the spring constant, it is necessary to move the leaf spring 7a below the position indicated by the number Q or above the position indicated by the symbol R. Although it is sufficient to set the load loading position, it is necessary to maintain the spacing between the fuel assemblies as described in - even if the length of the fuel assemblies varies during reactor operation. Since it is preferable to have the load loading position in the middle part of the length direction of the leaf spring 7a, it is difficult to have the load loading position lower than the Q position or higher than the R position. .

In consideration of the above points, in the present invention, as shown in FIG. In the figure, LS is the free length of the leaf spring 7a, TJf is the distance from the lower end of the leaf spring 7a to the fulcrum X of the leaf spring contact part, and Lt indicates the distance from the lower end of the leaf spring 7a to the load center position.

7 and 8 are both leaf spring characteristic diagrams of the channel fastener 7 shown in FIG. Same as the example.

Therefore, FIG. 7 is a diagram obtained by elastic calculation of the relationship between the distances J and f from the lower end of the leaf spring 7a to the fulcrum X of the leaf spring contact part shown in FIG. 6, and the stress and spring constant of the leaf spring 7a. The positions corresponding to the distances ■ and f from the lower end of the leaf spring 7a to the fulcrum X of the leaf spring contact portion are shown in FIG.
The curve A is the stress generated in the vicinity of the load, the curve B is the stress generated at the leaf spring fixing part, and the curve C is the fulcrum of the leaf spring abutting part. The stress generated at X, the curve is the spring constant, σ1-σ2 is the leaf spring 7
The range of maximum stress occurring in a, k, -2 is σ, -σ2
The range of the spring constant of the leaf spring 7a corresponding to is shown.

Note that σ0 and k. 4 respectively show the maximum stress and the spring constant of the leaf spring 7a, which is a component of the conventional channel fastener 7 shown in FIG.

As is clear from FIG. 7, if the distance from one end of the leaf spring 7a to the leaf spring abutment fulcrum X1 is set to 25 to 35% of the leaf spring offset length, the leaf spring 7
The stress of 21 is reduced by about 30-45%, and the spring constant is
Approximately 2 to 3 times larger.

Fig. 8 shows the point from the second end of the leaf spring 7a to the leaf spring abutting part fulcrum X.
-t is 30% of the leaf spring offset length, and the relationship between the distance LL from the lower end of the leaf spring 7a to the load center position and the stress and spring constant of the leaf spring 7a is determined by elastic calculation. In the diagrams obtained, curve A is the stress generated near the load application, curve B is the stress generated at the plate spring fixing part, and curve C is the stress generated at the fulcrum X of the plate spring contact part in Figure 6. is the spring constant, σ□8 is the maximum value of the stress generated in the leaf spring 7a, k□1. indicates the minimum value of the spring constant of the leaf spring 7a. In addition, σ. and ko indicate the maximum stress and spring constant of the leaf spring 7a, which is a component of the conventional channel fastener 7 shown in FIG. 4, respectively.

From FIG. 8, it can be seen that even if the length of the fuel assembly 1 changes during reactor operation, even if the distance L from the lower end of the leaf spring 7a to the load center position changes, compared to the conventional one, It can be seen that the stress of the leaf spring 7a is reduced by at least about 20%, and the spring constant is more than doubled.

FIG. 9 shows another embodiment of the present invention. In the embodiment shown in FIG. 9, a leaf spring contact portion 7 that shares the reaction force of the leaf spring 7a
1)', a protrusion is provided on the leaf spring support 7b, and the top of this protrusion is used as the fulcrum X of the leaf spring contact part. With this structure as well, it is different from the embodiment shown in FIG. A similar effect can be achieved.

As detailed above, according to the present invention, by only slightly changing the shape of the leaf spring support 7b, which is a component of the channel fastener 7 of the fuel assembly, compared to the conventional one,
The stress generated in the leaf spring 7a is significantly reduced, and the leaf spring 7a
Since the spring constant of (9) can be increased, the maximum amount of deflection of the leaf spring 7a can be increased, and the height of the leaf spring 7a in the direction of deflection can be increased to reduce the spacing between each fuel assembly. It is possible to obtain a fuel assembly spacing device that can increase the holding force and has excellent safety.

[Brief explanation of drawings]

Figure 1 is a partially cutaway perspective view showing the basic structure of a fuel assembly for a conventional (boiling water type) nuclear reactor, and Figure 2 is a unit cell forming a core unit of the fuel assembly shown in Figure 1. A plan view of the unit, FIG. 3 is a vertical sectional view showing an enlarged view of the channel fastener attachment part and its vicinity in the unit cell unit shown in FIG. 2, FIG. 4 is a partially enlarged view of FIG. 3, Fifth
The figure is a leaf spring characteristic diagram of the conventional channel fastener shown in Fig. 4, Fig. 6 is a vertical sectional view of the main part showing one embodiment of the present invention, and Figs. 7 and 8 are both shown in Fig. 6. FIG. 9 is a longitudinal sectional view of a main part showing another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Fuel assembly, 2...Fuel rod, 3...Support grid, 4(10)...-part tie plate, End...Lower type 1/-t, 6...Channel Box, 7... Channel fastener, 7a... Leaf spring, 7b... Leaf spring support, 7b'... Leaf spring contact portion, 7C... Leaf spring fixing screw, 8... Channel space Ther. Agent Patent attorney Hiroo Nagasaki (and 1 other person) (11) No. 1 Inhaya 2 Eye Haya 5 eyes 7c 7α 1 □ 1 7 no\ Ill 4th Loa (L Kaya 8 eyes PoZ'11 Ayu Ll 9th Close

Claims (1)

[Claims] 1. In a fuel assembly spacing device in which a channel fastener is attached to a corner of a channel box in which a plurality of fuel rods are loaded to elastically maintain space between adjacent channel boxes, the above-mentioned channel The leaf spring Zaport, which constitutes a part of the fastener, has a leaf spring abutting part located on three sides of the load bearing position of the leaf spring, which is another component of the channel fastener, and which shares the reaction force of the leaf spring. A fuel assembly spacing device comprising: