JP3195137B2 - 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 used in a boiling water reactor.

[0002]

Fuel assemblies for use in the Related Art For example boiling water reactor, a number of fuel rods and one or several of the water over rods bundled by the fuel spacers, top and bottom respectively upper tie and lower tie To form a fuel bundle, and the outer periphery of the fuel bundle is surrounded by a channel box serving as a fuel rod protection and control rod guide to form a fuel assembly.

That is, as shown in the cross-sectional view of FIG. 8, a conventional fuel assembly 1 has a large number of fuel rods 2 and water rods 3 arranged in a square, the upper end of which is an upper tie plate 4, and the middle of which is a plurality. The lower end of the fuel bundle 5 is supported by the lower tie plate 6 by the fuel spacer 5.

[0004] The fuel bundle 7 by inserting the channel box 8 from above, engages the upper tie plate 4 with clips 2箇provided in symmetry to the top corners of the channel box 8, of one of the Clip the upper tie plate 4
The fuel assembly 1 is fixed to the fuel assembly 1 with bolts 9 of a channel fastener.

[0005] The upper end of the fuel rod 2 is connected to an upper end plug 10.
The lower end is plugged with a lower end plug 11, and the upper end plug 10 has an upper tie plate 4 and a channel box 8.
Further, an expansion spring 12 for supporting the weight of the fuel rod 2 and absorbing the difference in extension of the fuel rod 2 is mounted.

[0006]

Since the channel box 8 of the fuel assembly 1 is fitted into the lower tie plate 6 at the beginning of the fuel life, its weight is supported by the lower tie plate 6. However, as the combustion of fuel progresses, the channel box 8 undergoes creep deformation (bulging) due to the difference in inner and outer thicknesses, and the lower tie plate 6
And a gap is created between them.

In this state, the weight of the channel box 8 is not supported by the lower tie plate 6 but is supported by the upper tie plate 4. If the weight of the channel box 8 is supported by the upper tie plate 4,
The expansion spring 12 must have a spring force capable of supporting the weight of the channel box 8 and the weight of the upper tie plate in order to absorb the difference in extension of the fuel rod 2.

However, since the spring force of the expansion spring 12 tends to decrease as the combustion proceeds, a high spring force is required by the expansion spring 12 in order to increase the burnup in the fuel assembly 1. For this reason, when the expansion spring 12 is enlarged and the assembly length is increased, it is necessary to shorten the fuel cladding tube (not shown) based on the current length of the fuel rod 2, which lowers the effective fuel efficiency. Leads to things.

On the other hand, the fuel rod 2 has a channel box 8
Is compressed, the fuel rods 2 are bent, which is not preferable from the viewpoint of appropriately securing the interval between the fuel rods 2. The channel box 8 is slightly deformed during use. The main deformation occurs due to the difference between the expansion of the coolant flowing through the channel box 8 due to the pressure and the irradiation growth by neutron irradiation. Note that this bend tends to bend such that a surface with a large neutron irradiation amount becomes convex.

Therefore, in the vicinity of the outer periphery of the core, the core is bent with the central direction of the core protruding, and if this deformation becomes large, it interferes with a control rod (not shown) and hinders the operation of inserting and withdrawing the control rod. appear.

As described above, the bend of the channel box 8 located on the outer periphery of the core becomes convex in the direction of the center of the core, so that one channel composed of one control rod and four fuel assemblies 1 is formed.
Looking at the two outermost cells, the channel box 8 of the fuel assembly 1 on the outermost periphery is bent toward the control rod, and the channel box 8 of the fuel assembly 1 in the second row from the outermost periphery on the core center side with the control rod interposed therebetween. Bends away from the control rod.

Accordingly, if the bend of the channel box 8 of the outermost fuel assembly 1 becomes large and there is a concern about interference with the control rods, the fuel assembly 1 can be moved to the second row from the outermost circumference in a parallel manner. Conversely, there is no hindrance because it bends away from the control rod. However, in the conventional fuel assembly 1, a fixing screw hole is threaded only in one of the corner posts of the upper tie plate 4, and a fixing hole is formed only in one of the clips in the channel box 8. Due to the clearance, the mounting position of the bolt 9 of the channel fastener is limited structurally.

For this reason, when the fuel assembly 1 is moved to the adjacent side in parallel, the position of the channel fastener of the adjacent fuel assembly 1 that is opposed to the channel fastener of the moved fuel assembly 1 is matched. As a result, it was difficult to secure a space for arranging control rods (not shown).

Incidentally, Japanese Patent Application Laid-Open No. 61-82191 proposed earlier
In the "fuel assembly" of the publication, a T-bar moving box is attached to the side surface of the channel box, and a coupling member attached to the upper tie plate is connected by a T-bar. Each deformation is prevented by not restricting the extension.

The "nuclear fuel assembly" disclosed in Japanese Patent Application Laid-Open No. 59-231475 has a structure in which the channel box is not directly fixed to the fuel bundle but is held by bolts of a channel fastener attached to the upper tie plate. Without restraining the axial movement of the channel box relative to each other, thereby preventing mutual deformation.

Furthermore, in the "nuclear fuel assembly" disclosed in Japanese Patent Application Laid-Open No. 55-117993, when the channel box is fixed to the fuel bundle, a long spring is used to press the channel fastener bolt with the projection into which the long spring is inserted. A mechanism is disclosed in which the extension of the channel box and the fuel rods is absorbed by the long spring, and the channel box is supported by the protrusions of the bolts of the channel fastener when the fuel bundle is lifted.

However, any of the above-mentioned disclosures can absorb the extension of the fuel rod and the channel box. However, as a measure against the bending of the channel box, it is necessary to appropriately change the direction by 180 degrees in each structure. It is difficult, and a strong spring is required in consideration of a decrease in the holding force of the channel box due to a decrease in the spring force of the spring.

An object of the present invention is to support the weight of the channel box by an upper tie plate via a coupling when moving and by using a lower tie plate when loading, so as to increase the burnup and improve the channel box. It is to provide a fuel assembly capable of bending.

[0019]

In order to achieve the above object, according to the first aspect of the present invention, a large number of fuel rods are bundled by a fuel spacer, the upper end is supported by an upper tie plate, and the lower end is supported by a lower tie plate. In a fuel assembly in which a fuel bundle is surrounded by a channel box, at least two diagonally opposite corners of the upper part of the upper tie plate are provided.
It is provided on one side so that it can be attached and detached.
A coupling having a projection, and the projection of the coupling enters.
Diagonally above each other at the top of the channel box
And a Kakaritomemado provided in two corners, the fuel assembly
With the upper edge of the locking window being loaded in the core.
It is characterized in that there is a space between the projection and the tool . The invention according to claim 2 of the present application provides the fuel according to claim 1.
In the assembly, connected to the bottom of the channel box
And a lower nozzle in contact with the lower tie plate is provided.
It is characterized by having.

[0020]

According to the fuel assembly of the present invention, when loaded in the core, the fuel bundle and the channel box are not fixed, so that the weight of the channel box does not add to the fuel bundle. In addition, the difference in extension between the fuel bundle and the channel box is not interfered by the coupling tool and is absorbed by the locking window of the channel box in a free state, so that they are not restricted to each other.

Further, during lifting, the fuel bundle connector is locked on the upper edge of the locking window of the channel box and is simultaneously lifted. Thus, the weight of the channel box adds to the upper tie plate of the fuel bundle and not to the fuel rods. Further, by loosening the bolt and moving the coupling outside the channel box, only the fuel bundle is lifted and the mounting direction of the channel box is changed.
It can be rotated 180 degrees and reinserted.

[0022]

An embodiment of the present invention will be described with reference to the drawings. The same components as those of the above-described conventional technology are denoted by the same reference numerals, and detailed description thereof will be omitted. As shown in the cross-sectional view of FIG. 1, taking a fuel assembly 13 for a boiling water reactor as an example, a lower nozzle 15 is previously connected to a channel box 14 with a screw 16 or the like, and a fuel bundle 17 is connected to a channel. It is inserted from above the box 14 and integrated. This assembling is the same even when the channel box 14 is placed from under the fuel bundle 17.

In the fuel bundle 17, a large number of fuel rods 2 and one or several water rods 3 are arranged in a square, the middle of which is bundled by a plurality of fuel spacers 5, the upper end of which is an upper tie plate 18, and The lower end is supported by a lower tie plate 19 having only a network, and the upper tie plate 18 and the lower tie plate 19 are connected by connecting fuel rods 20.

As shown by the enlarged perspective view of FIG. 2, Kakaritomemado 21 in the symmetric positions in the corner of the upper portion of the channel box 14 is Yes two spaced, further as shown in the plan view of FIG. 3 In the upper tie plate 18, a screw hole 23 is threaded on an upper end surface of a post 22 located at a corner corresponding to the locking window 21 of the channel box 14, and a coupling tool is installed in the screw hole 23. You. Therefore, the mounting of the channel box 14 can be changed in the direction of 180 degrees with respect to the upper tie plate 18.

As shown in the enlarged perspective view of FIG.
The base has an L-shape, and has an elongated hole 26 in the horizontal portion so that it can move in the direction of the arrow when the bolt 25 screwed to the post 22 of the upper tie plate 18 is loosened. In addition, the tip of the coupling tool 24 is a key-like projection 27, which is configured to be locked to the upper edge of the locking window 21 of the channel box 14.

FIG. 5 is a cross-sectional view of the fuel assembly 13. In the upper tie plate 18, the left side shows a state where the fitting 24 is installed at a predetermined position, and the right side shows a state where the channel box 14 is inserted.

Next, the operation of the above configuration will be described. In the lower part of the channel box 14, a lower nozzle 15 is
Are attached with screws 16. As shown in the right side of FIG. 5, the fuel bundle 17 is in a state where the bolts 25 are loosened and the two fasteners 24 are separated outward. The fuel bundle 17 in this state is lifted by a lifting tool (not shown) and inserted into the channel box 14.

When the lower tie plate 19 comes into contact with the lower nozzle 15, the connecting tool 24 is moved inward as shown on the left side of FIG. In this state, as shown in the enlarged perspective view of the coupling portion in FIG. 6, the key-like projection 27 at the tip of the coupling tool 24 enters into the locking window 21 of the channel box 14, but the upper edge of the locking window 21 and the key The assembly of the fuel assembly 13 is completed in a free state in which there is sufficient space with the projection 27. At this time, the weight of the fuel bundle 17 is added to the lower nozzle 15, which is the same state as when the core is loaded.

Next, when the handle 18a of the upper tie plate 18 is gripped and lifted, for example, to move the fuel assembly 13, the fuel bundle 17 directly connected to the upper tie plate 18 first rises, and then FIG. As shown in the enlarged perspective view of FIG. 3, the key-like projection 27 of the coupling tool 24 comes into contact with the upper edge of the locking window 21 and locks with the channel box 14.
Is lifted through the key-like projection 27. At this time, the weight of the channel box 14 and the lower nozzle 15 is added to the upper tie plate 18.

The removal of the channel box 14 is carried out by the reverse operation. In other words, the operation can be performed very easily by loosening the bolt 25, moving the two coupling tools 24 outward, gripping the handle 18a and lifting the fuel bundle 17 or pulling out the channel box 14.

In the fuel assembly 13 of the present invention, the channel bundle 14 and the fuel bundle
17 are not directly fixed, the weight of the channel box 14 is not applied to the fuel rods 2 and the expansion springs 12 throughout the entire life of the fuel, and their expansion is not restrained by each other. Absent.

The expansion spring 12 provided on the fuel rod 2
Compresses only in response to the extension of the fuel rod 2 and does not need to consider the weight of the channel box 14, so that the number of expansion springs 12 to be mounted or the spring force can be reduced. Expansion spring 12 from reduced spring force
By reducing the length of the fuel rod 2, the length of the fuel rod 2 can be reduced, or in the current length, the effective fuel length can be increased, and high burnup can be easily realized.

Incidentally, the fuel assembly 13, which is likely to interfere with the control rod due to the bending of the channel box 14 due to neutron irradiation or the like, is moved in parallel to the second row from the outermost periphery to hinder the operation of the control rod. Channel box 14 to eliminate
It is easy to take measures against bending.

That is, once the channel box 14 is detached from the fuel bundle 17 and re-assembled by changing the direction by 180 degrees, the two couplers 24 are connected to each other by the upper tie plate.
18 are arranged diagonally at the corners, and the locking window 21 of the channel box 14 for locking the same is provided at the same position, so that there is no problem.
Can be easily matched with the position of the channel fastener.

Further, in order to enable the channel box 14 to change its direction by 180 degrees with respect to the fuel bundle 17, the present invention is not limited to the configuration of the above-described embodiment.
If two places Kakaritomemado 21 in symmetric positions of the corners of the 14, coupler 24 to be installed in the upper tie plate 18 may be one.

[0036]

As described above, according to the present invention, the deformation of the fuel rod and the channel box due to elongation is suppressed, the interference with the control rod is eliminated, and the burnup of the fuel is increased.
There is an effect that the function of the fuel assembly can be improved by facilitating the mounting of the channel box by changing the direction by 180 degrees.

[Brief description of the drawings]

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

FIG. 2 is an enlarged perspective view of a main part of a channel box according to an embodiment of the present invention.

FIG. 3 is a plan view of an upper tie plate according to an embodiment of the present invention.

FIG. 4 is an enlarged perspective view of a coupler according to one embodiment of the present invention.

FIG. 5 is a sectional view of a fuel assembly according to an embodiment of the present invention.

FIG. 6 is an enlarged perspective view showing a free state of a connecting portion according to one embodiment of the present invention.

FIG. 7 is an enlarged perspective view showing a connection state of a connection portion of one embodiment according to the present invention.

FIG. 8 is a sectional view of a conventional fuel assembly.

[Explanation of symbols]

1, 13 ... fuel assembly, 2 ... fuel rod, 3 ... water rod, 4, 18 ... upper tie plate, 4a, 18a ... handle, 5 ... spacer, 6, 19 ... lower tie plate, 7, 17
... Fuel bundle, 8,14 ... Channel box, 9 ... Bolt of channel fastener, 10 ... Top end plug, 11 ... Lower end plug, 12 ... Expansion spring, 15 ... Lower nozzle, 16 ... Screw,
20 ... connecting fuel rod, 21 ... locking window, 22 ... post, 23 ... screw hole, 24 ... coupling tool, 25 ... bolt, 26 ... long hole, 27 ... key-like projection.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G21C 3/30

Claims (2)

(57) [Claims] 1. A top number of fuel rods bundled by the fuel spacer
In a fuel assembly in which a fuel bundle whose end is supported by an upper tie plate and whose lower end is supported by a lower tie plate is surrounded by a channel box, an upper portion of the upper tie plate is alternately provided.
A coupling tool removably provided at at least one of two corners located diagonally and having a projection on the channel box side; and a channel such that the projection of the coupling tool enters.
In the two corners at the top of the
And a Kakaritomemado that kicked, loaded the fuel assemblies in the reactor core
In the state in which the upper edge of the locking window is
A fuel assembly, characterized in that there is a space between them . 2. The device is coupled to a lower portion of the channel box.
And a lower nozzle in contact with the lower tie plate is provided.
The fuel assembly according to claim 1, wherein: