JPH0376879B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a fuel assembly, and particularly to a fuel assembly suitable for use in a boiling water nuclear reactor.

[Background of the invention]

For example, as an independent cell fuel spacer for a fuel assembly used in a nuclear reactor,
A fuel spacer having a structure as shown in FIG. 2A of Japanese Patent Publication No. 65287 and FIG. 1 of Japanese Patent Publication No. 55-38638 has been proposed.

FIG. 22 shows a fuel spacer proposed in the above-mentioned Japanese Patent Laid-Open No. 59-65287. This fuel spacer 1 has a large number of cylindrical members (independent cells) 3 into which fuel rods 6 are inserted arranged in a lattice pattern, and adjacent cylindrical members are connected to each other by welding parts W ₁
The outer periphery of a bundle of cylindrical members formed by welding and joining is surrounded by a belt-shaped side band 2, and the contact point (weld part W ₂ ) with the cylindrical member 3 is joined by welding. In addition, 4 and 5 in Figure 22
are a spring for supporting the fuel rod 6 and a protrusion protruding inside the cylindrical member 3, respectively.

The side wall of the cylindrical member 3 is provided with a C-shaped opening 7A for supporting the spring 4 as shown in FIGS. 23 and 24, and a notch 9 for forming the protrusion 5 as shown in FIG. It is being

The spring 4 used in the fuel spacer 1 is a continuous loop type spring formed from one circular ring. When attaching the spring 4 to the cylindrical member 3, first attach one side of the spring 4 to the C-shaped opening 7 of the cylindrical member 3.
A is inserted into the cylindrical member 3, and the cylindrical member 3 is rotated in this state. By this operation, the protruding piece 8A formed on the side wall of the cylindrical member 3 by providing the C-shaped opening 7A is inserted into the inside of the loop-shaped spring 4 (that is, the protruding piece 8A is inserted into the spring 4 around the protruding piece 8A). (surrounded by). Next, the vertical direction of the other cylindrical member 3 is reversed to that of the cylindrical member 3 with which the spring 4 is engaged (so that the opening 7A looks like a U-shape), and this cylindrical member 3 is By rotating the axis, the protruding piece 8A is inserted from the other entrance of the spring 4, and the upper and lower parts of the cylindrical members are joined by welding with the spring members of each side of the spring 4 pushed into the cylindrical member. , holds the spring 4.

FIG. 25 shows the fuel spacer 3 shown in FIG.
This is an enlarged part of the image. Figure 26 and 2
FIG. 7 shows the shapes of the S ₁₂ -S ₁₂ cross section and the S ₁₃ -S ₁₃ cross section of FIG. 25. The state in which the fuel rod 6 inserted into each cylindrical member 3 is supported by the spring 4 and the protrusion 5 is shown. Among the symbols in these figures, 4A indicates a convex portion provided at the longitudinal center of the spring 4, and 4B indicates convex portions provided at the upper and lower portions of the spring 4.

The independent cell fuel spacer described above has higher structural strength than the lattice-type fuel spacer used in fuel assemblies for boiling water reactors, so it reduces pressure loss by making the members thinner. Efforts are being made to reduce emissions and improve neutron economy. It has also been experimentally confirmed that this fuel spacer improves the thermal limits of the fuel rods.

However, when the inventors studied such an independent cell type fuel spacer, they discovered that the following new problem occurred in the independent cell type fuel spacer. That is, in the independent cell type fuel spacer, since two protruding pieces 8A of the cylindrical member 3 are arranged within the spring 4, the gap between the protruding piece 8A and the spring 4 is as follows.
Compared to a lattice-type fuel spacer (see Japanese Patent Application Laid-Open No. 59-63589, in which one lattice member is disposed within a spring), at least one protruding piece 8A is used.
It is narrower by the thickness of the wall. For this reason, the independent cell fuel spacer can exert a predetermined spring force in an extremely limited space, and at the same time, an extremely large load is applied to the spring 4 when inserting a fuel rod (when assembling a fuel assembly) or during an earthquake. Even when the spring 4 is loaded, it is necessary to prevent the spring 4 from losing its function as an elastic body due to damage or plastic deformation. Therefore, it is necessary to know in advance what kinds of problems may occur in the spring 4 during fuel rod insertion (assembly), earthquakes, and the like. Through investigation, the inventors found that the following problems occur.

28 and 29 show a case where the weld bead 6B of the fuel rod interferes with the convex portion 4B on the upper part of the spring when the fuel rod 6 is inserted into the cylindrical member 3. In this case, the weld bead 6B of the fuel rod
However, as can be seen from FIG. 29, the spring 4 is in contact with the upper protrusion 5 of the cylindrical member 3, and the inside of the spring 4 is in contact with the cylindrical member 3, so when the fuel rod 6 is forcibly inserted, the spring 4 The convex portion 4B at the upper end and its vicinity may be plastically deformed, and the protrusion 5 of the cylindrical member 3, the fuel rod tube portion 6A, etc. may be damaged.

30 and 31 show a case where the weld bead portion 6B interferes with the convex portion 4A at the center of the spring 4 when the fuel rod is inserted. In this case as well, if an attempt is made to insert more fuel rods, the same problem as in the case of FIG. 28 will occur.

FIGS. 32, 33, and 34 show a case where the weld bead 6B of the fuel rod and the lower protrusion 5 of the cylindrical member 3 interfere with each other. In this case, the inner side of the spring 4 is in contact with the protruding piece 8A of the cylindrical member 3 and the outer side is in contact with the tube part 6A of the fuel rod at the center and vicinity of the spring 4, so that the fuel rod 6 is further removed. When attempting to insert it, not only the protrusion 5 on the lower side of the cylindrical member 3 but also the convex portion 4A at the center of the spring and the fuel rod tube portion 6A that is in the vicinity or in contact with the convex portion 4A may be damaged by plastic deformation or other damage. will receive.

FIG. 35 shows that the fuel rods 6 spring against the springs 4 under load (acceleration) in the cross-sectional direction of the fuel assembly during an earthquake, during transportation of the fuel assembly, during handling of the fuel assembly, etc.
The figure shows a state in which the inner side of the spring 4 near the center of the spring 4 is in contact with the protruding piece 8A of the cylindrical member 3. In this case, the convex portion 4A at the center of the spring 4 is plastically deformed, and the tube portion 6A of the fuel rod 6 also receives a reaction force equivalent to the force of the fuel rod 6 pushing the spring 4 only at the contact portion with the spring 4. Therefore, a large stress is also generated in the tube portion 6A.

In addition, relatively simple countermeasures for the above-mentioned problems include, for example, reducing the outer diameter of the fuel rod to be applied from the perspective of securing a space for deformation of the spring 4, and leaving the outer diameter of the fuel rod unchanged. It is conceivable to lower the height of the protrusion 5 of the cylindrical member 3 and make the fuel rod 6 eccentric toward the protrusion 5. but,
When reducing the outer diameter of the fuel rod, the amount of nuclear reactant that can be loaded into the fuel rod 6 is necessarily reduced. Therefore, in order to maintain the nuclear fission reaction, it is necessary to increase the enrichment level, which increases the fuel cycle cost.
On the other hand, when the fuel rods are eccentrically moved toward the protrusion side, the spacing between the fuel rods becomes narrow in some parts, which is undesirable from both nuclear and thermal hydraulic viewpoints. In addition, as another countermeasure, the height of the convex portion 4A of the spring 4 (dimension h ₁ in FIG. 36) may be lowered to avoid the problems shown in FIGS. 30, 32, and 35. The method of preventing the occurrence and the height of the convex portion 4B of the spring 4 (third
Another possible method is to reduce the dimension h ₂ ) in FIG. 6 to prevent the problem shown in FIG. 28 from occurring.
However, the stress generated in the spring 4 due to deformation when the fuel rod 6 is inserted into the cylindrical member 3 is generally greatest at the center of the spring. Since the convex portion 4A also plays the role of keeping the stress low, from the viewpoint of the mechanical soundness of the spring 4, it is not preferable to reduce the height _h1 of the convex portion 4A. Also, spring 4
The gap between the fuel rod 6 and the fuel rod 6 becomes narrow near the convex portion 4A, and the flow of the coolant deteriorates, which is not preferable in terms of thermal hydraulic design. On the other hand, the convex portions 4 on the upper and lower sides of the spring
Lowering B is effective against the problem shown in FIG. 28, but it is not preferable because it actually exacerbates the problem shown in FIG. 35. In this way, the spring 4 is constructed to maintain a very delicate balance, and if the shape of the spring 4 is changed carelessly by focusing on only one problem, other problems will be exacerbated. Changing the shape of the spring is not a very desirable method as it may cause new problems.

The present invention has been made in order to solve the newly discovered problems based on the above study results by the inventors.

[Purpose of the invention]

An object of the present invention is to provide a fuel assembly that can reduce the risk of damage to cell-type fuel spacers and improve the neutron utilization rate.

[Summary of the invention]

A feature of the present invention is that the volume of the spring support inserted into the loop spring is reduced to increase the space in which the loop spring deforms.

The first structure of the fuel assembly of the present invention is such that the wall thickness of the spring support portion in the direction perpendicular to the axis of the cylindrical body of the cell type fuel spacer is equal to the thickness of both cylindrical bodies at the contact position of the adjacent cylindrical bodies. It is thinner than the total thickness of the body.

Furthermore, in the second structure of the fuel assembly of the present invention, the spring support portion provided in the cylindrical body of the cell-type fuel spacer is inserted into the loop-shaped spring at the upper and lower ends of the loop-shaped spring. , and is not inserted into the loop-shaped spring in the vicinity where the convex portion of the loop-shaped spring exists.

Note that a cell-type fuel spacer includes a plurality of cylindrical bodies into which fuel rods are inserted and which are provided in contact with each other, and a plurality of cylindrical bodies which are provided at a position where adjacent cylindrical bodies are in contact with each other and come into contact with the fuel rods. It includes a loop-shaped spring having a convex portion and the cylindrical body having a spring support portion that supports the loop-shaped spring.

[Embodiments of the invention]

A fuel assembly that is a preferred embodiment of the present invention will be described below. Although not shown, the fuel assembly of this embodiment has an upper tie plate, a lower tie plate, and both ends of each tie plate, as shown in FIG. 1 of JP-A-59-65287. It is equipped with a large number of fuel rods and cell-type fuel spacers.

The cell type fuel spacer used in this example is:
In the structure of the cell type fuel spacer shown in FIG. 22, the cylindrical member 3 is replaced with a cylindrical member 3A which is an independent cell shown in FIG. 1. In the cell type fuel spacer, fuel rods 6 are inserted into the cylindrical member 3A as shown in FIG. 4, and the gap between adjacent fuel rods 6 is maintained at a predetermined width. A plurality of cell-type fuel spacers are arranged in the axial direction of the fuel assembly.

The structure of the cell type fuel spacer used in this embodiment will be explained in detail with reference to FIGS. 1, 2, 3, and 4.

Cylindrical member 3 constituting the cell type fuel spacer
A has an E-shaped opening 7B in the side wall. By forming the E-shaped opening 7B, a pair of protrusions 8B ₁ and 8 function as spring supports for the loop spring 4.
_B2 is formed on the side wall of the cylindrical member 3A. Projection piece 8
_B1 is located above the protruding piece _8B2 . A pair of protrusions 5 are provided at the upper and lower ends of the cylindrical member 3A. These protrusions 5 are elongated cuts 9 along the circumferential direction in the side wall of the cylindrical member 3A (see FIG. 3).
After applying this, a part of the cylindrical member 3A is formed to protrude inward.

The cylindrical members 3A are arranged in a grid pattern like the cylindrical members 3 in FIG. 22. Adjacent cylindrical member 3A
are joined by welding at the upper and lower ends where they contact each other. _W1 in Figure 3 is the welded part. 1
One cylindrical member 3A is joined to four other adjacent cylindrical members 3A at four locations. Adjacent cylindrical members 3A are joined by welding when the protrusions 8B ₁ and 8B ₂ of one cylindrical member 3A are connected to the protrusions 8 of one of the four adjacent cylindrical members 3A.
This is done so that B ₁ and 8B ₂ are in contact with each other.
One loop-shaped spring 4 is installed at a position where the projecting pieces 8B ₁ and 8B ₂ are in contact with each other, that is, at a position where a pair of adjacent cylindrical members 3A are in contact, as shown in FIG. A pair of contacting protrusions 8B ₁ are inserted into the spring 4 at the upper end of the loop spring 4 and support the upper end of the loop spring 4. contact 1
The pair of projecting pieces 8B ₂ are inserted into the spring 4 at the lower end of the loop-shaped spring 4, and support the lower end of the loop-shaped spring 4. The loop spring 4 has one half (the right half in FIG. 3) inside one cylindrical member 3A, and the other half (the left half in FIG. 3) inside the cylindrical member 3A.
It is located inside another cylindrical member 3A adjacent to A. Convex portions 4A and 4B are formed on each portion of the loop-shaped spring 4 located within both cylindrical members 3A, and these convex portions 4A are used to guide the fuel rods 6 inserted into the corresponding cylindrical members 3A. is pressed in the radial direction. Not only when the loop spring 4 is not attached to the cylindrical member 3A, but also when it is attached to the cylindrical member 3A, the inner surfaces of the pair of convex portions 4A provided on the loop spring 4 have a space. Directly facing each other. This is because a central gap Z1, _which is a part of the E-shaped opening _7B , is formed between the protruding piece 8B1 and the protruding piece _8B2 . That is, when the loop spring 4 is installed in both adjacent cylindrical members 3A, the spring is supported within the loop spring 4 at the center in the height direction of the loop spring 4, that is, at the position where the convex portion 4A exists. There is no protruding piece, and the inner surfaces of the pair of protrusions 4A of the loop spring 4 directly face each other with a central gap _Z1 in between.

Next, attachment of the loop-shaped spring 4 to the cylindrical member 3A will be explained. First, one side of the loop-shaped spring 4 is inserted into the E-shaped opening 7B of the cylindrical member 3A, and then the cylindrical member is inserted so that the projecting pieces 8B ₁ and 8B ₂ of the cylindrical member 3A enter the loop-shaped spring 4 from one entrance. The member 3A is rotated around its axis. Next, the vertical direction of the other cylindrical member 3A is reversed to that of the cylindrical member 3A with which the loop spring 4 is engaged so that the E-shaped opening 7B looks like a Y-shape, and then the reversed cylinder The projecting pieces 8B ₁ and 8B ₂ of the member 3A are inserted into the loop spring 4 from the other entrance on the opposite side. Finally, the relative angle between the two cylindrical members 3A is adjusted so that the center of the protrusion 5 of the cylindrical member 3A is inclined by a predetermined angle with respect to the straight line connecting the centers of the adjacent cylindrical members 3A, and the welded portion W ₁ and both cylindrical members 3
A is welded and the loop spring 4 is attached to the projecting pieces 8B ₁ and 8.
Hold with B ₂ .

As shown in FIGS. 5 and 6, according to this embodiment, when the fuel rod 6 is inserted into the cylindrical member 3A during fuel assembly assembly, the pipe portion 6B of the fuel rod 6
The center part (convex part 4
A and its vicinity) are the cylindrical member 3A where it exists.
It is pushed from the side toward another cylindrical member 3A adjacent thereto. In this case, the center portion of the loop-shaped spring 4 to be pushed is the E-shaped opening 7B of the cylindrical member 3A.
inserted into the central gap Z ₁ of. Therefore, the deformation of the loop spring 4 due to the passage of the weld bead portion 6A can be absorbed by the center gap _Z1 , so that the loop spring 4 does not lose its function as an elastic body due to excessive deformation. Protrusion 5 of fuel rod 6 or cylindrical member 3A
can be prevented from being damaged.
Furthermore, according to this embodiment, as shown in FIGS. 7 and 8, large accelerations are applied in the cross-sectional direction of the fuel assemblies during earthquakes, during transportation and handling of the fuel assemblies, and the fuel rods 6 moves in the direction of contact with the loop spring 4 (in the direction of arrow A in the figure),
Central part of loop-shaped spring 4 (convex part 4A and its vicinity)
is inserted into the central gap _Z1 , which is the above-mentioned spatial space, so that plastic deformation of the loop spring 4 can be prevented. Furthermore, in this case, the fuel rod 6
moves toward the loop spring 4, the fuel rod 6
comes into contact not only with the convex portion 4A of the loop-shaped spring 4 but also with the upper and lower convex portions 4B with a predetermined amount of movement, so that the reaction force that the fuel rod 6 receives from the loop-shaped spring 4 can be dispersed. . Therefore, generation of excessive stress on the fuel rods 6 can also be prevented.
FIG. 9 shows this effect. FIG. 9 shows the relationship between the acceleration G in the cross-sectional direction that the fuel assembly receives during an earthquake, etc., and the pressure F that the fuel rod 6 receives from the loop spring 4 at that time. In FIG. 9, F ₁ is the initial reaction force of the loop-shaped spring 4, and F ₂ is the reaction force of the loop-shaped spring 4 caused by the fuel rod 6.
This is the reaction force of the loop-shaped spring 4 when it comes into contact with the upper and lower convex portions 4B. Further, G ₁ is the acceleration of the fuel rod 6 when the force pushing the loop spring 4 and the reaction force of the loop spring 4 are balanced, and G ₂ is the acceleration of the fuel rod 6 when the force pushing the loop spring 4 is balanced with the reaction force of the loop spring 4. This is the acceleration when contacting with. In the case of a conventional cell-type fuel spacer, the fuel rod 6 always contacts only the convex portion 4A of the loop spring 4 and does not contact the upper and lower convex portions 4B (see Fig. 35), so that the acceleration G and The relationship between the reaction force F that the fuel rod 6 receives from the loop spring 4 is expressed by the ninth
It becomes like the two-dot chain lines P ₁ to _{P 2} to P ₃ to _{P 4} in the figure. On the other hand, in the case of the cell-type fuel spacer used in this embodiment, for the reason mentioned above, the solid lines P ₁ -P ₂ -P ₃ -P ₅ and the dashed-dotted lines P ₆ -P ₇ in FIG. become that way. From FIG. 9, the cylindrical member 3A shown in FIG.
By using a cell-type fuel spacer equipped with this, the reaction force that the fuel rods 6 receive from the loop spring 4 is significantly reduced, which is very effective in maintaining the mechanical integrity of the fuel rods 6. One thing will be easily understood. Therefore, the allowable range of applicable fuel rod outer diameters can be significantly widened.

Furthermore, in this embodiment, compared to the cell type fuel spacer used in the conventional example shown in FIG _.
and 8B ₂ ) have decreased in volume. This is because the amount of structural material of the cell-type fuel spacer used in this example is reduced, and the amount of neutrons absorbed by the fuel spacer is reduced. Therefore, of the neutrons generated in the fuel assembly of this embodiment, the amount of neutrons that contribute to new nuclear fission increases, and it is possible to increase the neutron utilization rate, that is, improve the neutron economy.

By providing the central gap _Z1 , it is possible to achieve both the function of reducing the risk of damage to the cell-type fuel spacer, in particular the risk of damage to the loop spring 4, and the function of improving the neutron economy. There is.

In addition, in this example, there is no need to change the shape of the loop spring itself or the method of holding the loop spring from the conventional one, and on the other hand, the processing performed on the independent cells is extremely partial and slight, and the independent cells Since only one type is required, assembly of the fuel spacer is easy.

FIG. 10 shows a cell type fuel constituting a fuel assembly according to another embodiment of the present invention, and shows a cylindrical member of a spacer. This cell type fuel spacer will be explained with reference to FIGS. 10, 11, 12, and 13. In the embodiment described above, an E-shaped opening 7B was formed in the side wall of the cylindrical member to form a protrusion for holding the loop spring 4, and the cross-sectional shape of the protrusion remained arcuate. However, the cell type fuel spacer used in this embodiment uses the cylindrical member 3B. This cylindrical member 3B is provided with a C-shaped opening 7C in the side wall, and most of the protruding piece 8C formed thereby is made flat, so that the distance between the center of the plate thickness of the protruding piece 8C and the center of the cylindrical member 3B is Attach the protruding piece 8C to the cylindrical member 3 so that it is half of the fuel pitch.
It is made to protrude to the outside of B. The protruding piece 8C serving as a spring support portion is a part of the cylindrical member 3B that protrudes, and the thickness of the protruding piece 8C and the thickness of the cylindrical member 3B are equal.

Figures 12 and 13 show a cylindrical member 3B with a loop spring 4 installed by welding the upper and lower parts at the welding part _W1 .
This figure shows the state when the fuel rod 6 is inserted into the inside. In this case, two adjacent cylindrical members 3B
The projecting piece 8C is a space spacer Z ₂ which is a part of the C-shaped opening 7C formed in the mating cylindrical member 3B.
(See Figure 10). In the cell type fuel spacer used in this example,
The length of the formed protrusion 8C along the axial direction of the cylindrical member is such that even when the cylindrical members 3B are combined, the two protrusions 8C do not interfere and the end surfaces of the protrusion 8C face each other with almost no gap. Since it is set to , the state is the same as when a single flat spring support member is inserted into the loop-shaped spring 4. Therefore, according to this embodiment, there are two in the loop spring 4.
Compared to a conventional cell-type fuel spacer that has a structure in which two protrusions are inserted (see Fig. 30), the space in which the loop spring 4 can deform is increased by at least the thickness of one protrusion. Problems during fuel rod insertion as shown in Figures 28, 30, and 32 (damage to loop spring 4, cylindrical member 3B, etc.)
can be prevented. In addition, in the case of this embodiment, the height of the upper and lower convex portions 4B of the loop spring 4 (dimension h ₂ in FIG. 36) is set to the height of the convex portion 4A (the third
By making the dimension slightly larger than the dimension h ₁ ) in FIG. 6, the same effect as the above-mentioned embodiment can be obtained even in the event of an earthquake. Furthermore, since the total volume of the protrusions passing through the loop spring 4 is reduced compared to that of conventional cell-type fuel spacers, neutron economy can be improved.

A cell-type fuel spacer constituting a fuel assembly according to another embodiment of the present invention will be described with reference to FIGS. 14 to 17. The cylindrical member 3C used in this embodiment has a C-shaped opening 7D in its side wall, thereby forming a protruding piece 8D. However, Figures 10-1
In the embodiment shown in FIG.
When the protruding pieces 8C are joined together, the end faces of the protruding pieces 8C face each other with almost no gap (see Fig. 12). The gap between the end faces of the two projecting pieces 8D is the same as that of the cylindrical member 3 shown in FIG.
The length is set to be the same as the gap between the end faces of the two upper and lower projecting pieces 8B ₁ and 8B ₂ of A (see FIGS. 3 and 16). Therefore, as can be seen from FIG. 16, in this embodiment, when the adjacent cylindrical members 3C are joined, the central gap _Z1 shown in FIG. 3 is substantially formed between the upper and lower projecting pieces 8D. It turns out. The space corresponding to the central gap Z ₁ is the space Z ₃
formed by a part of Furthermore, the state is the same as when a single flat member separated vertically passes through the loop-shaped spring 4. For this reason, Figures 3 and 1
The functions that occur in both structures shown in FIG. 2 occur in this embodiment, and the space for deforming the loop-shaped spring 4 becomes dramatically larger than that of the conventional structure, and the neutron economy is also significantly improved. These effects are shown in Figure 3 and Figure 1.
It is larger than the structure shown in Figure 2.

In addition, in the above description of the embodiment, only the case where the cross-sectional shape of the independent cells constituting the cell-type fuel spacer is circular, but the case where the cross-sectional shape of the independent cells is polygonal such as octagon or hexagon is applicable. The present invention can also be applied to obtain similar effects. Each figure shown in FIG. 18 to FIG. 21 shows a rectangular tube member 10 in which the first embodiment of the present invention is applied to an independent cell (square tube member 10) having an octagonal cross-sectional shape, and this rectangular tube member 10.
The figure shows a state in which a fuel rod 6 is inserted after a spring 4 is attached to the rectangular tube members and the rectangular tube members are connected by welding. All the symbols are the same as those shown in FIGS. 1 to 4 except for the rectangular tube member 10. Second
As can be seen from a comparison between FIG. 0 and FIG. 3, the support methods for the springs 4 and fuel rods 6 are the same in both cases, except for the different shapes of the independent cells. Therefore, even when the cross-sectional shape of the independent cell is polygonal, it is fully possible to apply each of the embodiments of the present invention, and it is easily understood from these figures that the above-mentioned effects can be obtained. be understood.

〔Effect of the invention〕

According to the present invention, damage to the cellular fuel spacer,
In particular, the risk of damage to the loop spring can be reduced, and neutron economy can be improved.

[Brief explanation of drawings]

FIG. 1 is a side view of an independent cell of a cell-type fuel spacer used in a fuel assembly according to an embodiment of the present invention, FIG. 2 is a sectional view taken along _S1 - _S1 in FIG. 1, and FIG. Figure 1 is a cutaway side view showing a normal fuel rod support state in a cell-type fuel spacer using independent cells, Figure 4 is a sectional view taken along _S2 - _S2 in Figure 3, and Figure 5 is the structure of Figure 3. Figure 6 is a cross-sectional view taken along S ₃ - S ₃ of Figure 5, and Figure 7 is a fractured side view of the structure shown in Figure 3 showing how the fuel rods are supported during an earthquake. Figure 8 is the S ₄ - S ₄ cross section of Figure 7, Figure 9 is the 3rd cross section.
An explanatory diagram showing the relationship between acceleration and the reaction force that the fuel rod receives from the loop spring in the structure shown in the figure. Figure 10 is a cell-type fuel used in a fuel assembly that is another embodiment of the present invention. A side view of the independent cell of the spacer, FIG. 11 is a cross-sectional view of S ₅ - S ₅ in FIG. 10,
FIG. 12 is a cutaway side view showing a fuel rod insertion state in the cell-type fuel spacer using the independent cells shown in FIG _{. 10} , FIG.
4 is a side view of an independent cell of a cell-type fuel spacer used in a fuel assembly according to another embodiment of the present invention, FIG. 15 is a sectional view taken along _S7 - _S7 of FIG. 14, and FIG.
The figure is a cutaway side view showing a state in which fuel rods are inserted in the cell-type fuel spacer using independent cells in FIG.
FIG. 17 is a sectional view taken along S ₈ -S ₈ in FIG.
Figure 9 is a sectional view of _S9 - _S9 in Figure 18, and Figure 20 is a cross-sectional view of Figure 1.
Figure 8 is a cutaway side view showing the fuel rod support state in a cell-type fuel spacer using octagonal independent cells, Figure 21 is a sectional view taken along S ₁₀ - S ₁₀ in Figure 20, and Figure 22 is a conventional cell-type fuel spacer. A plan view of the spacer, FIG. 23 is a side view of an independent cell for a conventional cell-type fuel spacer, FIG. 24 is a sectional view taken along S ₁₁ - S ₁₁ in FIG.
Figure 5 is a plan view showing the fuel rod support state in a conventional cell-type fuel spacer, and Figure 26 is the same as Figure 25.
S ₁₂ - S ₁₂ sectional view, Fig. 27 is S ₁₃ - S ₁₃ in Fig. 25
The sectional view, FIG. 28, FIG. 30, and FIG. 32 are cutaway side views showing problems when inserting fuel rods into conventional cell-type fuel spacers, and FIG. 29 is a cross-sectional view of FIG.
S ₁₄ - S ₁₄ sectional view, Fig. 31 is S ₁₅ - S ₁₅ in Fig. 30
A cross-sectional view, FIG. 33 is a cross-sectional view of S ₁₆ - S ₁₆ in FIG. 32,
FIG. 34 is a cutaway side view taken in the - arrow direction of FIG. 33, and FIG. 35 is a cutaway side view showing how fuel rods are supported by a conventional cell fuel spacer during an earthquake.
FIG. 36 is a cutaway side view showing how fuel rods are supported in a conventional cell-type fuel spacer. 1...Fuel spacer, 2...Side band,
3, 3A, 3B, 3C...independent cell (cylindrical member),
4...Loop-shaped spring, 4A, 4B...Protrusion, 5...
...Protrusion, 6... Fuel rod, 6A... Fuel rod tube part,
6B... Lower end plug weld bead of fuel rod, 6C...
...lower end plug of fuel rod, 7A, 7B, 7C, 7D...
...Notch, 8A, 8B, 8C, 8D... Projection, 9
... Cut, 10 ... Independent cell (rectangular tube member with octagonal cross section), W ₁ ... Weld between independent cells, W ₂ ... Weld between independent cells and side bands, Z ₁ , Z ₂ , Z ₃ ……
Spring passage space or ridge storage space.

Claims (1)

[Scope of Claims] 1. A fuel assembly including a plurality of fuel rods and a fuel spacer that maintains a distance between the fuel rods, wherein the fuel spacers are in contact with each other while the fuel rods are inserted therein. a plurality of cylindrical bodies provided in a plurality of cylindrical bodies; a loop-shaped spring having a convex portion provided at a position where the adjacent cylindrical bodies contact each other and contacting the fuel rod; and a loop-shaped spring inserted into the loop-shaped spring. the cylindrical body having a spring support part that supports the loop-shaped spring, and the wall thickness of the spring support part in the direction perpendicular to the axis of the cylindrical body is equal to that of the adjacent cylindrical body. A fuel assembly characterized by being thinner than the sum of the wall thicknesses of both cylindrical bodies at a contact position. 2. Claim 1, wherein the cylindrical body is a cylinder.
Fuel assembly as described in section. 3. In a fuel assembly including a plurality of fuel rods and a fuel spacer that maintains a distance between the fuel rods, the fuel spacer has a plurality of fuel rods inserted therein and provided in contact with each other. a cylindrical body; a loop-shaped spring having a convex portion that is provided at a position where the adjacent cylindrical bodies contact each other and contacts the fuel rod; and a cylindrical body having a spring support portion that supports the loop-shaped spring. the spring support part is inserted into the loop spring at the upper and lower ends of the loop spring, and the loop spring is inserted into the loop spring in the vicinity of the protrusion of the loop spring. A fuel assembly characterized in that it is not inserted into a spring. 4 Claim 3, wherein the cylindrical body is a cylinder
Fuel assembly as described in section. 5. In a fuel assembly including a plurality of fuel rods and a fuel spacer that maintains a distance between the fuel rods, the fuel spacer has a plurality of fuel rods inserted therein and provided in contact with each other. a cylindrical body; a loop-shaped spring having a convex portion that is provided at a position where the adjacent cylindrical bodies contact each other and contacts the fuel rod; and a cylindrical body having a spring support portion that supports the loop-shaped spring. the spring support part is inserted into the loop spring at the upper and lower ends of the loop spring, and the loop spring is inserted into the loop spring in the vicinity of the protrusion of the loop spring. The thickness of the spring support portion in the direction perpendicular to the axis of the cylindrical body that is not inserted into the spring is the sum of the wall thicknesses of both adjacent cylindrical bodies at the contact position. A fuel assembly characterized by being thinner than the fuel assembly. 6 Claim 5, wherein the cylindrical body is a cylinder
Fuel assembly as described in section.