JP3103201B2 - Nuclear fuel assembly - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel assembly of a boiling water reactor, and more particularly to a nuclear fuel assembly having an improved spacer structure.

[0002]

2. Description of the Related Art In general, a fuel assembly of a boiling water reactor generally has a plurality of fuel rods arranged in a square lattice, at least one water rod, and the fuel rods and the water rods are arranged at predetermined intervals. And a plurality of spacers to be held. In this nuclear fuel assembly, it has been studied to use a partial length fuel rod having a shorter overall length than a normal fuel rod for a part of the fuel rod.

[0003] Conventional nuclear fuel assemblies using a partial length fuel include a spacer located above an upper end of a partial length fuel rod and a spacer located below an upper end of a partial length fuel rod, as described in, for example, JP-A-63-120292. And have different shapes,
Specifically, the spacer located below the upper end of the partial length fuel rod has a structure in which the round cells are located at all positions corresponding to the fuel rod, and the spacer located above is located at the position corresponding to the partial length fuel rod. Except for the round cell.

[0004]

In the above prior art, it is possible to reduce the pressure loss by deleting a part of the round cell. However, it is clear that the strength of the spacer is reduced when the round cell at the position of the partial length fuel rod is simply removed, and this point is not taken into account in the above-described conventional technology, and the strength reliability of the spacer is reduced. There was a problem.

An object of the present invention is to provide a nuclear fuel assembly in which the strength of the spacer is improved by securing the strength of the spacer while reducing the pressure loss.

[0006]

According to the present invention, a plurality of fuel rods arranged in a square lattice, at least one water rod, and a fuel rod and a water rod are provided. A plurality of spacers which are held at a predetermined interval, wherein the plurality of spacers are respectively connected to a plurality of round cells, a band located on the outer periphery of these round cells, and a plurality of bands provided on the band. In the nuclear fuel assembly having a plurality of opposed bathtubs, the plurality of spacers have the round cells at all positions corresponding to the fuel rods between the opposed bathtubs, and the fuel cells in other areas are provided with the round cells. A nuclear fuel assembly is provided, comprising at least one first spacer without the round cell at least in a corresponding position.

In the above nuclear fuel assembly, preferably, the round cells between the opposed bathtubs are arranged so that the center thereof coincides with the center of the bathtub. The round cells between the opposed bathtubs may be arranged such that the boundary between two adjacent round cells coincides with the center of the bathtub.

According to the present invention, a plurality of fuel rods arranged in a square lattice, at least one water rod,
A plurality of spacers for holding the fuel rods and the water rods at predetermined intervals, wherein the plurality of fuel rods includes a partial length fuel rod having a short overall length, and the plurality of spacers are respectively connected to each other. In a nuclear fuel assembly having a round cell, a band located on the outer periphery of the round cell, and a plurality of bathtubs provided in the band, facing each other,
Among the plurality of spacers, the spacer located above the upper end of the partial length fuel rod has the round cell at all positions corresponding to the fuel rod between opposed bathtubs, and at least the portion of the other region The nuclear fuel assembly is characterized in that the round cell is not provided at a position corresponding to the long fuel rod, and the partial length fuel rod is located only below the position of the first spacer where the round cell is not provided. Provided.

Further, according to the present invention, a plurality of fuel rods arranged in a square lattice, at least one water rod,
A plurality of spacers for holding the fuel rods and the water rods at predetermined intervals, wherein the plurality of fuel rods includes a partial length fuel rod having a short overall length, and the plurality of spacers are respectively connected to each other. In a nuclear fuel assembly having a round cell, a band located on the outer periphery of the round cell, and a plurality of bathtubs provided in the band, facing each other,
Spacer positioned above the upper end of said part length fuel rods of the plurality of spacers, there is the round cells for all positions corresponding to the fuel rods between the tub facing a predetermined location of the other regions Wherein the nuclear fuel assembly is provided without the round cell , and at least a portion of the partial length fuel is located below the position of the first spacer where the round cell is absent.

Further, according to the present invention, a plurality of fuel rods arranged in a square lattice, at least one water rod,
A plurality of spacers for holding these fuel rods and water rods at predetermined intervals, wherein the plurality of spacers are each connected to a plurality of round cells, and a band located on the outer periphery of these round cells; In the nuclear fuel assembly having a plurality of opposed bathtubs provided on the band, the plurality of spacers have the round cells at all positions corresponding to the fuel rods between the opposed bathtubs, A plurality of first spacers that do not have the round cells in at least a part of the position corresponding to the fuel rods in the area, and the round cells are located at all positions corresponding to the fuel rods between opposed bathtubs; A nuclear fuel assembly is provided, wherein a position where the round cell is absent in other regions includes a plurality of second spacers shifted from the first spacer. In this case, preferably, the first spacer and the second spacer
Are alternately arranged in the axial direction of the fuel rod at least every other spacer.

[0011]

[Function] In a nuclear fuel assembly, when a load acts on a fuel rod from the channel box due to flow vibration or earthquake,
In any case where the load acts on the channel box from the fuel rods, the load is transmitted via a bathtub which is a projecting member of a band provided on the outer periphery of the spacer. The bathtub is
Usually, two pieces are provided on each side of the square band, and a total of eight pieces are provided so as to face each other on the opposite side. Therefore, when a load in the direction parallel to the side is applied,
Each of the bathtubs bears the above load. In this case, it is not desirable in terms of strength reliability to remove cells located between the opposing bathtubs. That is, when the cell is removed, the transmission path of the load is obstructed, and the welded portion in the vicinity of the obstructed portion is predicted to be subjected to the tensile load or the shear load from the deformation difference between the cells. .

Therefore, in order to ensure the strength of the spacer, it is important not to remove the cells in the immediate vicinity of the bathtub, especially to not remove the cells located between the opposed bathtubs 3.

The present invention has been made based on the above-mentioned study, and it is assumed that a cell other than a cell located between opposing bathtubs is made a removable cell, and at least a part of this cell is removed, thereby forming a spacer. Pressure loss can be reduced without impairing strength.

There are several ideas as to which cells other than those located between the opposing bathtubs are to be removed.
In the case of a nuclear fuel assembly including a partial length fuel rod, the spacer located above the upper end of the partial length fuel rod is removed only when the partial length fuel rod is arranged at a position of a removable cell. Thereby, all the fuel rods can be supported by the spacer, and the pressure loss can be reduced without impairing the strength of the spacer. In this case, if the partial length fuel rods are not arranged at the positions corresponding to the cells located between the opposed bathtubs in advance, the cells can be removed at the positions corresponding to all the partial length fuel rods, and the reduction in pressure loss is the largest. Become.

Further, first and second spacers in which positions where there is no round cell in the area other than between the opposing bathtubs may be used are different from each other. The fuel rod is always supported by any of the spacers. In this case, it is preferable that the first and second spacers are alternately arranged every other one, thereby ensuring the soundness of the fuel rod. In this spacer structure, since the position without the round cell can be set regardless of the presence or absence of the partial length fuel rod, the present invention can also be applied to a spacer of a fuel assembly having no partial length fuel rod.

In consideration of the case where the load acts on the channel box due to flow vibration or earthquake in the positional relationship between the cell and the bathtub, in order to achieve smooth transfer of the load, it is necessary to match the centers of the cell and the bathtub. It is desirable that the boundary between the two cells coincides with the center of the bathtub.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. First, a first embodiment of the present invention will be described with reference to FIGS. 1 and 2, the nuclear fuel assembly of the present embodiment is arranged in a plurality of fuel rods 7 arranged in a 10 × 10 square lattice and a 2 × 2 lattice area at the center of the fuel rod arrangement. One large-diameter water rod 8A, and four small-diameter water rods 8B arranged point-symmetrically around the water rod 8A;
It has a plurality of spacers 4A, 4B for holding these fuel rods 7 and water rods 8A, 8B at predetermined intervals. Most of the fuel rods 7 are full-length fuel rods having a normal length,
A part thereof is a partial length fuel rod 7a whose overall length is shorter than a normal full length fuel rod. As shown by the crosses in FIG. 2, the partial length fuel rods 7a are adjacent to the center of each side of the outermost circumference of the fuel rod array, two by two, and adjacent to the large diameter water rod in a point symmetrical manner. A total of twelve pieces are arranged for each two pieces. The upper ends of the full length fuel rod 7 and water rods 8A and 8B are upper tie plates 9
, And the lower end is supported by the lower tie plate 10. The periphery of the fuel rods 7, 7a and the water rods 8A, 8B is surrounded by a channel box (not shown) to complete a nuclear fuel assembly.

The spacer 4A is disposed below the upper end of the partial length fuel rod 7a, and the spacer 4B is disposed above the upper end of the partial length fuel rod 7a. The spacer 4A is shown in FIG.
As shown in the figure, a large number of round cells 1 for searching and supporting the fuel rods 7, 7a at positions corresponding to the fuel rods 7, 7a, and the water rods 8A, 8A, 8B at positions corresponding to the water rods 8A, 8B.
8B, which have round cells 5A and 5B that search through and support 8B.
These round cells 1 and 5A, 5B are formed of cylindrical structural members, and adjacent cells are connected to each other by spot welding the upper and lower ends at the boundary between them. A square band 2 is provided on the outer periphery of each of the round cells 1 and 5A, 5B.
Is provided. Two bathtubs 3 are provided on each side of the square shape of the band 2, and a total of eight bathtubs 3 are provided on opposite sides. The round cells 1 between the opposing bathtubs 3 are arranged such that their centers coincide with the centers of the bathtubs 3,
The width of the bathtub 3 is substantially equal to the diameter of the round cell 1. In addition,
The width of the bathtub 3 may be smaller than the diameter of the round cell 1.

On the other hand, as shown in FIG. 4, the spacers 4B are arranged at a position corresponding to the full length fuel rods 7 and a number of round cells 1 for searching and supporting these fuel rods 7, and at positions corresponding to the water rods 8A and 8B. And round cells 5A and 5B for searching and supporting these water rods 8A and 8B. There is no round cell at the position corresponding to the partial length fuel rod 7a. Round cells 1 and 5A, 5
B is also formed of a cylindrical structural member, and adjacent cells are connected to each other by spot welding of upper and lower ends at a boundary between the cells. A square band 2 is provided on the outer periphery of each of the round cells 1 and 5A and 5B, and a bathtub 3 as a projecting member is provided on the outer surface of the band 2. Two bathtubs 3 are provided on each side of the square shape of the band 2, and a total of eight bathtubs 3 are provided on opposite sides. The round cells 1 between the opposing bathtubs 3 are arranged so that the center thereof coincides with the center of the bathtub 3, and the width of the bathtub 3 is substantially equal to the diameter of the round cell 1. In addition, the width of the bathtub 3 may be smaller than the diameter of the round cell 1.

That is, in the spacer 4B, the round cells 1 are located at all positions corresponding to the fuel rods 7 between the opposed bathtubs 3, and the partial length fuel rods 7a are located in other areas.
There is no round cell at the position corresponding to the above, and the partial length fuel rod 7a is located only below the position of the spacer 4B where there is no round cell.

In this embodiment, the principle of adopting the above configuration for the spacer 4B is as follows. The adjacent cells 1 in the spacer structure of the nuclear fuel assembly are connected to each other by spot welding the upper and lower ends at the boundary between the two as described above. Therefore, when a tensile load or a shear load acts on the welded portion, the strength reliability decreases. On the other hand, the function of the spacer is to maintain the interval between the fuel rods 7 by the cell 1, which is a constituent member.

When a load acts on the fuel rod 7 due to flow vibration or earthquake, the load is transmitted from the fuel rod 7 to the cell 1 holding the fuel rod 7, and further transmitted between adjacent cells.
Power is transmitted to a channel box from a bathtub 3 which is a projecting member of a band 2 provided on the outer periphery of the spacer. That is, the bathtub 3 provided on the band 2 of the spacer bears the above load. On the other hand, when a load acts on the channel box due to a flow vibration or an earthquake, the load is transmitted to each cell 1 along a path reverse to the above. According to an example analyzed separately, the stress of the cell in the immediate vicinity of the bathtub 3 is increased in any case. Therefore, the removal of the cell in the immediate vicinity of the bathtub 3 has a large effect on securing the strength of the spacer, and is not desirable.

As described in this embodiment, usually, two bathtubs 3 are provided on each side of the square band 2 and a total of eight bathtubs 3 are opposed to each other on the opposite sides. Therefore, when a load in the direction connecting the vertices of the square band 2 is applied, four bathtubs 3 on adjacent sides are applied, and when a load in a direction parallel to the side is applied, two bathtubs 3 on one side are applied.
However, each bears the above load.

When the directions of action of the two loads are compared, it goes without saying that the parallel direction in which the two bathtubs 3 bear the load greatly affects the strength of the spacer. Removing the intervening cell 1 is not desirable in terms of strength reliability. That is, when the cell is removed, the transmission path of the load is obstructed, and the welded portion in the vicinity of the obstructed portion is predicted to be subjected to the tensile load or the shear load from the deformation difference between the cells. .

Further, in the above-described analysis example, the stress of the outermost peripheral cell other than immediately adjacent to the bathtub becomes particularly small. Further, in the spacer having the large-diameter water rod 5A disposed in the center as in this embodiment, the vicinity of the water rod The stress of the cell located at becomes smaller. Therefore, removing the cell at the low stress portion does not affect the strength of the spacer.

In consideration of the case where the load acts on the channel box due to flow vibration or earthquake in the positional relationship between the cell 1 and the bathtub 3, in order to achieve smooth transmission of the load, the cell 1 and the bathtub 3 are required. Or the boundary between the two cells 1 should be aligned with the center of the bathtub 3. That is, when a load is applied from the bathtub 3 to the plurality of cells 1 in a non-equilibrium manner, a deformation difference occurs between the two, and it is considered that a shear stress acts on a welded portion connecting the two. The shear stress reduces the strength reliability of the spacer as described above.

As described above, the spacer located above the upper end of the partial length fuel rod 7a does not remove the cells immediately adjacent to the bathtub 3, and in particular, does not remove the cells located between the opposed bathtubs 3. It is important to secure Further, if the partial length fuel rod 7a is not disposed in advance at that position, it is possible to remove the cell at a position corresponding to the partial length fuel rod in the spacer located above the upper end of the partial length fuel rod.

In the present embodiment, based on the above study, the spacer 4B located above the upper end of the partial length fuel rod 7a, as shown in FIG. The cell 1b (broken line) at a position other than the position (1) is a removable cell, and the cell 1b is removed only when the partial length fuel rod 7a is arranged at the position of the removable cell 1b. Therefore, according to the present embodiment, the pressure loss can be reduced without impairing the strength of the spacer, and a margin of the flow stability can be increased, and a highly reliable nuclear fuel assembly can be realized.

FIG. 6 shows a modification of the above embodiment. This figure 6
Fig. 1 shows the concept of applying the present invention to a nuclear fuel assembly having a plurality of fuel rods arranged in a 9 x 9 square lattice and having no large-diameter water rod. In the drawing, members that are the same as the members shown in FIG. 5 are given the same reference numerals.

In this embodiment, in the spacer located above the upper end of the partial length fuel rod 7a (see FIG. 1), the round cell 1a between the opposing bathtubs 3 is defined by the boundary between two adjacent round cells 1a. 3, so that the width of the bathtub 3 is substantially equal to the diameter of the round cell. Then, the cell 1 located between the opposed bathtubs 3
A cell 1b (broken line) at a position other than a (solid line) is a removable cell, and the cell 1b is removed only when the partial length fuel rod 7a is arranged at the position of the removable cell 1b.

According to this embodiment, the pressure loss can be reduced without deteriorating the strength of the spacer.

FIG. 7 shows another modification of the above embodiment. FIG. 7 shows a nuclear fuel assembly having a plurality of fuel rods arranged in a 10 × 10 square lattice and having two large-diameter water rods and two small-diameter water rods. 9 shows an example in which is applied. In the figure, members that are the same as the members shown in FIG. 4 are given the same reference numerals.

In this embodiment, in the spacer 4C located above the upper end of the partial length fuel rod, all the positions corresponding to the full length fuel rod are located between the opposed bathtubs 3 as in the embodiment of FIG. In the other region, there is no round cell at the position corresponding to the partial length fuel rod, and the partial length fuel rod 7a is located only below the position of the spacer 4B where there is no round cell. In addition, the round cells 5A and 5B that search and support these water rods are arranged with the use of two large-diameter water rods and two small-diameter water rods. The position where there is no round cell, that is, the position of the partial length fuel rod is the same as that of the embodiment of FIG. According to this embodiment, the pressure loss can be reduced without deteriorating the strength of the spacer.

A second embodiment of the present invention will be described with reference to FIGS. In FIG. 8, the nuclear fuel assembly according to the present embodiment includes spacers 4 alternately arranged in the axial direction of the fuel rods 7.
D, 4E, and the other configuration is the same as that of the first embodiment. As shown in FIG. 9, the spacer 4D has the round cells 1 at all positions corresponding to the fuel rods 7 between the opposed bathtubs 3, and the round cells are removed at predetermined positions in other areas. . As shown in FIG. 10, the spacers 4E also have the round cells 1 at all positions corresponding to the fuel rods 7 between the opposed bathtubs 3, and the round cells are removed at predetermined positions in other areas. . However, spacer 4
In D and the spacer 4E, the positions from which the round cells have been removed complement each other. That is, the round cell 1 is located at the position where the round cell is removed by the spacer 4D, and the round cell 1 is located at the position where the round cell is removed by the spacer 4E. Therefore, every other fuel rod 7 located at the cell removal position is provided with every other spacer 4D or 4D.
The fuel rod is supported by E, and the soundness of the fuel rod is not impaired.

According to this embodiment, the pressure loss can be reduced without impairing the strength of the spacer by the same principle as that of the first embodiment.

FIGS. 11 and 12 show a modification of the second embodiment. In this embodiment, similarly to the above embodiment, spacers 4F and 4G are alternately arranged in the axial direction of the fuel rod 7, and the spacers 4F and 4G are provided between the opposed bathtubs 3 by the fuel rod 7. At all the corresponding positions, there is a round cell 1, and in other regions, the round cells are removed at positions complementary to each other. In the present embodiment, the spacers 4F and 4F
G has the same shape by rotating one of them by 90 °.

Therefore, according to the present embodiment, since the design and production can be achieved with one spacer shape, the pressure loss can be reduced with a cheaper configuration without impairing the strength of the spacer.

In the embodiment shown in FIGS. 8 to 12, the present invention is applied to the fuel assembly having the partial length fuel rod 7a. However, the position without the round cell can be set regardless of the presence or absence of the partial length fuel rod. Therefore, the same effect can be obtained even when applied to a fuel assembly having no partial length fuel rod.

[0039]

According to the present invention, it is possible to remove the cell which is a constituent member while securing the strength of the spacer in the nuclear fuel assembly, which has a great effect on the improvement of the strength reliability. As the margin of stability increases, a highly reliable nuclear fuel assembly can be realized.

[Brief description of the drawings]

FIG. 1 is an external view of a nuclear fuel assembly according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG.

FIG. 3 is a plan view of a spacer located below an upper end of the partial length fuel rod shown in FIG. 1;

FIG. 4 is a plan view of a spacer located above an upper end of the partial length fuel rod shown in FIG. 1;

FIG. 5 is a diagram for explaining the principle of the embodiment shown in FIG. 1;

FIG. 6 is a view for explaining the principle of a modification of the embodiment shown in FIG. 1;

FIG. 7 is a view showing a spacer according to another modification of the embodiment shown in FIG. 1;

FIG. 8 is an external view of a nuclear fuel assembly according to a second embodiment of the present invention.

FIG. 9 is a plan view of one of the two types of spacers shown in FIG.

FIG. 10 is a plan view of the other of the two types of spacers shown in FIG.

FIG. 11 is a plan view of one of two types of spacers in a modification of the first embodiment.

FIG. 12 is a plan view of the other of the two types of spacers.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cell 2 Band 3 Bathtub 4A-4G Spacer 5A, 5B Cell for water rod installation 7 Fuel rod 7a Partial length fuel rod 8A, 8B Water rod

Continuing from the front page (72) Inventor Kenji Kanamori 3-1-1, Sachimachi, Hitachi-shi, Ibaraki Pref. Hitachi, Ltd. Hitachi Plant (72) Inventor Hajime Umehara 3-1-1, Sachimachi, Hitachi-shi, Ibaraki Stock Hitachi, Ltd. Hitachi Plant (72) Inventor Shozo Nakamura 502, Kandate-cho, Tsuchiura-shi, Ibaraki Pref. Machinery Research Laboratory, Hitachi, Ltd. (72) Inventor Tadashi Mizuno 502, Kantate-cho, Tsuchiura-City, Ibaraki Pref. (72) Inventor Masatoshi Inagaki 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd.Hitachi Laboratory (72) Inventor Hajio Aoyama 1168 Moriyama-cho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd.Energy Laboratory (72) Inventor Yasunori Bessho 3-1-1, Sachimachi, Hitachi-shi, Ibaraki Pref. Hitachi, Ltd. Hitachi Plant (72) Inventor Yasuhiro Aizawa 3-2-1, Sachimachi, Hitachi-shi, Ibaraki Pref. Hitachi Engineering Co., Ltd. (72) Inventor Shinji Sakata Thorn 502, Kandachi-cho, Tsuchiura-shi, Castle Inside Machinery Research Laboratory, Hitachi, Ltd. (56) References JP-A-5-150068 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G21C 34

Claims (11)

(57) [Claims] 1. A plurality of fuel rods arranged in a square lattice,
At least one water rod, and a plurality of spacers for holding the fuel rods and the water rods at predetermined intervals, the plurality of spacers being respectively connected to a plurality of round cells, In the nuclear fuel assembly having a band located on the outer periphery of the band and a plurality of bathtubs provided on the band and facing each other, the plurality of spacers are located at all positions corresponding to the fuel rods between the opposed bathtubs. A nuclear fuel assembly comprising the round cell and at least one first spacer without the round cell in at least a part of a position corresponding to the fuel rod in another region. 2. The nuclear fuel assembly according to claim 1, wherein
The plurality of fuel rods include a partial length fuel rod having a short overall length, the first spacer is located above an upper end of the partial length fuel rod, and the partial length fuel rod is located at the round cell of the first spacer. A nuclear fuel assembly characterized by being located only below a position where no fuel is present. 3. The nuclear fuel assembly according to claim 1, wherein
The plurality of fuel rods include a partial length fuel rod having a short overall length, the first spacer is located above an upper end of the partial length fuel rod , and at least a portion of the partial length fuel rod is the first fuel rod.
The nuclear fuel assembly, wherein the spacer is located below the position where the round cell does not exist. 4. The nuclear fuel assembly according to claim 1, wherein
The plurality of spacers include the round cells at all positions corresponding to the fuel rods between the opposed bathtubs, and at least one of the other regions where the positions without the round cells are shifted from the first spacer. A nuclear fuel assembly comprising a second spacer. 5. The nuclear fuel assembly according to claim 4, wherein
The nuclear fuel assembly, wherein the first spacers and the second spacers are alternately arranged in the axial direction of the fuel rod. 6. The nuclear fuel assembly according to claim 1, wherein
A nuclear fuel assembly, characterized in that the round cells between the opposed bathtubs are arranged so that the center thereof coincides with the center of the bathtub. 7. The nuclear fuel assembly according to claim 1, wherein
A nuclear fuel assembly, wherein the round cells between the opposed bathtubs are arranged such that the boundary between two adjacent round cells coincides with the center of the bathtub. 8. A plurality of fuel rods arranged in a square lattice,
At least one water rod, and a plurality of spacers for holding the fuel rods and the water rods at predetermined intervals, wherein the plurality of fuel rods include a partial length fuel rod having a short overall length, and the plurality of spacers A plurality of round cells coupled to each other, a band positioned on the outer periphery of these round cells, and a plurality of opposed bathtubs provided on the band; The spacer located above the upper end of the partial length fuel rod has the round cells at all positions corresponding to the fuel rod between opposed bathtubs, and corresponds to at least the partial length fuel rod in other areas. The nuclear fuel assembly, wherein the round cell is not located at the position where the round cell is located, and the partial length fuel rod is located only below the position of the first spacer where the round cell is absent. 9. A plurality of fuel rods arranged in a square lattice,
At least one water rod, and a plurality of spacers for holding the fuel rods and the water rods at predetermined intervals, wherein the plurality of fuel rods include a partial length fuel rod having a short overall length, and the plurality of spacers A plurality of round cells coupled to each other, a band positioned on the outer periphery of these round cells, and a plurality of opposed bathtubs provided on the band; Among them, the spacer located above the upper end of the partial length fuel rod has the round cells at all positions corresponding to the fuel rods between opposed bathtubs, and the round cells at predetermined positions in other areas. And at least a portion of the partial-length fuel is located below the position of the first spacer where there is no round cell. 10. A fuel cell comprising: a plurality of fuel rods arranged in a square lattice; at least one water rod; and a plurality of spacers for holding these fuel rods and water rods at predetermined intervals. In a nuclear fuel assembly having a plurality of round cells, each of which has a plurality of round cells coupled to each other, a band located on the outer periphery of these round cells, and a plurality of mutually opposite bathtubs provided in the band, The spacer has the round cells at all positions corresponding to the fuel rods between the opposed bathtubs, and a plurality of first cells without the round cells at at least a part of positions corresponding to the fuel rods in other areas. The spacers and the round cells are located at all positions corresponding to the fuel rods between the opposed bathtubs, and the positions where the round cells are absent in other regions are shifted from the first spacer by a plurality of third cells. A nuclear fuel assembly comprising: a second spacer; 11. The nuclear fuel assembly according to claim 10, wherein the first spacers and the second spacers are alternately arranged in the axial direction of the fuel rod at least every other spacer. Nuclear fuel assembly.