JPH08320391A - Fuel assembly for boiling water reactor - Google Patents

Abstract

(57) [Summary] [Objective] To obtain a boiling water reactor fuel assembly capable of coping with deformation of a channel box and maintaining a leak flow control function even if a high burnup fuel is used. [Structure] A boiling water reactor fuel assembly has a leak control that controls the amount of coolant leakage from the gap between the lower portion of the channel box and the outer peripheral surface of the lower tie plate on the side surface of the lower tie plate. This leak control plate has a plurality of slits at intervals in the direction orthogonal to the axial direction of the fuel assembly, and the interval between the slits is at the center as compared with the region near the corner portion of the lower tie plate. It is characterized by a narrower area.

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]

2. Description of the Related Art Generally, a fuel assembly used in a boiling water reactor (BWR) has a plurality of fuel rods 9 formed by spacers 10 arranged in the axial direction of the fuel rods, as shown in FIG. And the required water pipes (not shown) in the central part are bundled in a square lattice shape, and this is held by the upper tie plate 7 and the lower tie plate 6 that forms an inflow path for cooling water from the lower part of the core, and the upper part A channel box 8 is fixed to the tie plate 7 to cover the entire fuel assembly.

In the lower tie plate 6 of such a fuel assembly, in order to constantly control the outflow of the coolant at the lower end of the channel box due to the pressure difference between the inside and outside of the channel box 8 when the fuel is used in the actual furnace. Further, a leak control plate 41 is provided to prevent the coolant from leaking out from the inside of the channel box through the gap between the channel box 8 and the lower tie plate 6 at the lower end when the channel box 8 is bulged. The increase in flow rate is limited.

Here, the lower tie plate 6 of the fuel assembly
The part is shown in FIG. FIG. 5A shows a lower tie plate 6.
It is a perspective view of. A leak control plate 41 is attached to each side surface of the lower tie plate 6, and the leak control plate 41 has a lower portion in a lower pocket (not shown) provided on the lower side surface of the lower tie plate 6. After being inserted, the upper portion is inserted into an upper pocket (not shown), and the upper portion is held by the stopper plate 4 so as to maintain a predetermined clearance (spacing) in the upper pocket. It is fixed by 5.

As shown in FIG. 5B, the leak control plate 41 is provided with a plurality of windows 43 of the same size for circulating the coolant at equal intervals. Four
Slits 42 are provided between each of them.

The leak control plate 4 mounted in this way
Since No. 1 can move freely within the clearance of the pocket (not shown) of the lower tie plate 6, the internal / external pressure difference (internal pressure> external pressure) is generated in the channel box 8 in the actual furnace, and the channel box 8 swells. In this case, the leak control plate 41 is pressed against the inner wall of the channel box 8 due to this pressure difference and deforms following the deformation of the channel box 8. Therefore, the leakage and outflow of the coolant from the gap at the lower end of the channel box is controlled to be constant. It will be.

As another structure of the leak control plate, there has been proposed a structure using the spring property of the plate material as shown in FIG. This is generally called a finger spring 51, and as shown in FIG. 6 (a), the plate material is bent at a plurality of predetermined positions in the width direction of the plate material (that is, in the direction parallel to the bending line of the plate material). On the other hand, slits 52 extending in a substantially vertical direction are provided at equal intervals in the width direction so as to have a spring property. FIG. 6C is a front view of such a finger spring 51.

The upper portion of the finger spring 51 is bent almost perpendicularly to the springy portion and is in contact with the upper surface of the lower tie plate 6. Figure 6
6B is a top view of the finger spring 51. As shown in FIG.
The upper part of 1 is formed in a ring shape, and the lower end plug insertion hole 5 for passing the lower end plug of the fuel rod through each ring part 5
0 is provided. Therefore, this lower end plug insertion hole 50
When the control rod is inserted into each of the lower tie plates 6
Will be attached to the side.

In the actual furnace, the finger springs 51 thus mounted have a difference in internal and external pressures (internal pressure> external pressure) in the channel box 8 and the channel box 8
When it swells, it follows the inner wall of the channel box 8 within the range of its own elasticity, so it deforms following the deformation of the channel box 8, and the coolant leaks out from the gap at the lower end of the channel box. Will be controlled to be constant.

[0010]

In recent years, a high burnup of a fuel assembly for a boiling water reactor has been investigated, and further increase of the burnout average burnup from 45 GWd / t has been studied. ing.

Generally, the channel box undergoes a bulge deformation as shown in FIG. 7 when an internal / external pressure difference (internal pressure> external pressure) occurs. Since this bulge deformation is composed of elastic deformation and creep deformation, the amount of deformation increases due to the creep deformation that increases with the progress of the baking degree (longer use of the channel box).

The leak control plate is deformed following the deformation of the channel box and controls the leak flow rate within a certain range. However, in consideration of the high burnup of the boiling water reactor fuel assembly, If the burnup of the channel box increases and the use of the channel box is prolonged, the amount of deformation of the channel box will increase more than before, so the leak control plate will exceed the range that can follow the deformation of the channel box. There is.

That is, when a fuel having a higher burnup than that conventionally used is used, the channel box is used for a long period of time, so that the boiling water type fuel assembly leaks especially at the end of combustion. The control function of the flow rate cannot be maintained, the leak flow rate increases and the effective cooling water flow for removing heat from the fuel rods decreases.

Therefore, according to the present invention, the deformation of the channel box can be satisfactorily dealt with even when a fuel having a high burnup is used.
An object of the present invention is to obtain a fuel assembly for a boiling water reactor capable of maintaining the control function of the leak flow rate.

[0015]

In order to achieve the above object,
According to the invention of claim 1, the outer circumference of a bundle of a plurality of fuel elements and the like arranged in parallel between the upper tie plate and the lower tie plate is suspended by the upper tie plate from the lower tie plate. A leak control plate is provided on the outer peripheral side surface of the lower tie plate to cover the outer peripheral side surface and to control the amount of coolant leaking from the gap between the lower portion of the channel box and the outer peripheral side surface of the lower tie plate. In the boiling water reactor fuel assembly, a plurality of slits extending along the axial direction of the fuel assembly are provided in the leak control plate at intervals in a direction orthogonal to the axial direction, and the slits are provided. It is characterized in that the space between them is narrower in the central region than in the region near the corners of the lower tie plate.

The invention of claim 2 is directed to the fuel assembly for a boiling water reactor of claim 1, wherein the interval between the plurality of slits is directed from a position close to a corner portion of the lower tie plate to a central position. It is characterized by gradually narrowing.

[0017]

As described above, the channel box undergoes bulge deformation, which is elastic deformation and creep deformation, when a pressure difference such that the internal pressure> the external pressure is generated between the inside and the outside of the channel box.

FIG. 7 is a sectional view of the channel box when the channel box undergoes bulge deformation. As shown in FIG. 7, the bulge deformation causes the center of the side surface to be apex on each of the four side surfaces of the channel box. Is a deformation that expands in a protruding shape toward the outside, and the amount of deformation increases as the burn-up of a high burnup fuel progresses (longer use of the channel box).

Here, it can be said that the leak control plate attached to the lower tie plate of the fuel assembly has a larger amount of deformation as the gap between the slits is narrower, and can easily follow the deformation of the wall surface of the channel box.

In the bulge deformation, the amount of deformation is small in the region close to the corner and the amount of deformation is large in the central region. A leak control plate is used in which the gap between the slits is narrowed in the central region where the amount of deformation is large.

As a result, even if the channel box undergoes the bulge deformation as described above, the leak control plate deforms following the large deformation of the wall surface of the channel box in the central region thereof, and in the region near the corners. Since the leakage flow rate is controlled satisfactorily by following the small deformation of the wall surface, it is possible to obtain a boiling water nuclear reactor fuel assembly in which the leakage flow rate control function can be favorably maintained.

Further, in the invention of claim 2, the distance between the plurality of slits is preferably from the position close to the corner portion of the lower tie plate to the central position according to the curvature of the bulge deformation of each side portion of the channel box. It is equipped with a leak control plate that gradually narrows toward.

Since the bulge deformation of the channel box is a deformation in which each of the four side surfaces of the channel box expands outward with the center of the side surface as the apex, the deformation amount of the wall surface of the channel box is the lower tie plate. It gradually increases from the side corners toward the center.

Therefore, in order to make such a bulge deformation form as close as possible, the mutual intervals of the slits provided in the leak control plate are gradually narrowed from the position near the corner portion of the lower tie plate toward the central position. , The amount of deformation of the leak control plate gradually increases from the region near the corner of the lower tie plate with small bulge deformation toward the central region with large bulge deformation, and A deformability suitable for bulge deformation can be provided, the followability of the leak control plate with respect to the deformation of the channel box can be enhanced, and the reliability of the leak control function for high burnup fuel can be improved.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below with reference to three embodiments, but the same or corresponding parts in all the drawings are designated by the same reference numerals.

FIG. 1 is a schematic explanatory view showing a first embodiment of the present invention. FIG. 1 (a) shows a leak control plate 1 on a side surface of a lower tie plate 6 of a fuel assembly for a boiling water reactor. Lower tie plate 6 showing a state where the stopper plate 4 is inserted and attached
It is a perspective view of a part.

Since the leak control plate 1 is attached to the lower tie plate 6 so as to maintain a predetermined clearance, the leak control plate 1 is movable within this clearance range.

The leak control plate 1 has a plurality of slits 2 for allowing the leak control plate 1 to follow the expansion of the channel box 8 and a window 3 provided between the slits 2 for allowing a coolant to pass therethrough. It has and.

As shown in FIG. 1B, the slits 2 are large in the central region and small in the regions near the corners. Therefore, the slit pitch in the central region is small and the slits in the regions near the corners are small. The slit pitch is large.

Since the window 3 provided between the plurality of slits 2 is formed in a size corresponding to the slit pitch, the width is narrow in the central region and wide in the region near the corners. There is.

Due to such a structure, the leak control plate 1 has the channel box 8 in its central region.
It is possible to control the leak flow rate satisfactorily by performing a deformation following the large deformation of the channel box 8 and a deformation following the small deformation of the channel box 8 in the region near the corner.

Therefore, even when a fuel having a higher burnup than that conventionally used is used, it is possible to favorably deal with the deformation of the channel box 8 and maintain the control function of the leak flow rate. It becomes a boiling water reactor fuel assembly.

FIG. 2 is a schematic explanatory view showing a second embodiment of the present invention. FIG. 2 (a) shows a leak control plate on the side surface of the lower tie plate 6 of the fuel assembly for a boiling water reactor. 21
FIG. 7 is a perspective view of a lower tie plate 6 portion showing a state in which the stopper plate 4 is attached by inserting the.

Since the leak control plate 21 is attached to the lower tie plate 6 so as to maintain a predetermined clearance, the leak control plate 21 can move within this clearance range.

The leak control plate 21 has a plurality of slits 22 for allowing the leak control plate 21 to follow the expansion of the channel box 8, and a window 23 provided between the plurality of slits 22 for allowing the coolant to pass therethrough. Is equipped with.

The slits 22 are spaced apart from each other as shown in FIG.
As shown in (b), the lower tie plate 6 is provided so as to be gradually narrowed from a position close to the corner portion toward the central position. Therefore, the slit pitch gradually increases from the corner portion to the central portion. It is getting smaller.

Window 2 provided between a plurality of slits
Since 3 is formed to have a size corresponding to the slit pitch, the width is gradually narrowed from the corner portion to the central portion.

With such a configuration, the leak control plate 21 is deformed according to the curvature of the bulge deformation of each side portion of the channel box 8, and therefore the leak control plate 21 against the deformation of the channel box 8 is formed. It is possible to obtain a fuel assembly for a boiling water reactor, which has a high following characteristic and an improved reliability of a leak control function for a high burnup fuel.

Therefore, even when a fuel having a higher burn-up than that used conventionally is used, it is possible to satisfactorily deal with the deformation of the channel box and keep the control function of the leak flow rate boiling. It becomes a fuel assembly for a water reactor.

Further, FIG. 3 is a schematic explanatory view showing a third embodiment of the present invention. FIG. 3 (a) shows a finger spring 31 on the side surface of the lower tie plate 6 of the boiling water reactor fuel assembly. FIG. 6 is a perspective view of a lower tie plate 6 portion showing a state in which is attached as a leak control plate.

The finger spring 31 is made of a plate material which is continuously bent into a mountain shape and a valley shape at predetermined intervals.
The width direction of the plate (that is, the direction parallel to the bending line of the plate)
On the other hand, a plurality of slits 32 extending in a direction substantially perpendicular to the above are provided to provide a spring property.

FIG. 3B shows a finger spring 31.
FIG. 3 is a front view of the finger spring 31. As shown in FIG. 3B, the slits 32 provided in the finger spring 31 are large in the central region and small in the regions near the corners. Therefore, the slit pitch in the central region is small and the slit pitch in the region near the corner is large.

Further, the upper portion of the finger spring 31 is formed in a ring shape as disclosed in the conventional example of FIG. 6 (b), and the control rod is inserted into the lower end plug insertion hole provided in each ring portion. By doing so, the elastic portion of the finger spring 31 is attached to the side surface of the lower tie plate 6 and functions as a leak control mechanism.

The finger spring 3 having such a configuration
In No. 1, when an inner-outer pressure difference (internal pressure> external pressure) occurs in the channel box 8 in the actual furnace and the channel box 8 swells, the channel box 8 is deformed to follow the large deformation of the channel box 8 and is close to the corner portion. In the region, the channel box 8 is deformed following a small deformation, so that the outflow of the coolant from the gap at the lower end of the channel box 6 can be well controlled.

Therefore, even when a fuel having a higher burnup than that used conventionally is used, the deformation of the channel box 8 can be satisfactorily dealt with and the function of controlling the leak flow rate can be maintained. It becomes a boiling water reactor fuel assembly.

[0046]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, a fuel for a boiling water reactor capable of coping well with the deformation of the channel box even when a fuel having a high burnup is used and maintaining the control function of the leak flow rate. The effect of being able to obtain an aggregate is achieved.

When a fuel having a higher burn-up than that conventionally used is used, even if the channel box is used for a long time and the amount of bulge deformation increases, the leak control plate responds to this bulge deformation state. Since it has the deformability, it achieves the effect that the leak flow rate can be always controlled to be constant during the entire period from the early stage of combustion to the final stage of combustion.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing a first embodiment of the present invention.

FIG. 2 is a schematic explanatory view showing a second embodiment of the present invention.

FIG. 3 is a schematic explanatory view showing a third embodiment of the present invention.

FIG. 4 is a schematic explanatory view showing the structure of a BWR fuel assembly.

FIG. 5 is a schematic explanatory view showing a conventional example.

FIG. 6 is a schematic explanatory view showing another conventional example.

FIG. 7 is a cross-sectional view showing a basil deformation state of a channel box.

[Explanation of symbols]

1, 21, 31, 41, 51 Leak control plate 2, 22, 32, 42, 52 Slit 3, 23, 43 Window 4 Stop plate 5 Bolt 6 Lower tie plate 7 Upper tie plate 8 Channel box 9 Fuel rod 10 Spacer 50 Lower end plug insertion hole

Claims (2)

[Claims] 1. A peripheral side surface of the lower tie plate by a channel box suspended from the upper tie plate at the outer circumference of a bundle of a plurality of fuel elements and the like arranged in parallel between the upper tie plate and the lower tie plate. Boiling with a leak control plate on the outer peripheral side surface of the lower tie plate, which covers the lower part of the channel box and controls the leakage amount of the coolant from the gap between the lower part of the channel tie plate and the outer peripheral side surface of the lower tie plate. In the water reactor fuel assembly, the leak control plate is provided with a plurality of slits extending along the axial direction of the fuel assembly at intervals in a direction orthogonal to the axial direction, A fuel assembly for a boiling water reactor characterized in that the slits are narrower in the central region than in the region near the corners of the lower tie plate. 2. The boiling water reactor according to claim 1, wherein the intervals between the plurality of slits are gradually narrowed from a position near a corner portion of the lower tie plate toward a central position. Fuel assembly.