JPH0943373A - Fuel assembly for boiling water reactor - Google Patents

Abstract

To provide a fuel assembly for a boiling water nuclear reactor equipped with a leak control plate capable of controlling the leak flow rate well even when the pressure difference between the inside and the outside of the channel box is small. SOLUTION: A leak control plate that occupies most of the width dimension of the side portion on the outer peripheral surface of the lower tie plate of the fuel assembly for a boiling water reactor is arranged in the thickness direction in the vertical cross section along the axial direction of the assembly. By making the center of gravity offset to the channel box side, it is easy to fall toward the channel box side, the pressure difference between the inside and outside of the channel box is small, and even if the bias due to the leak flow from the back side of the leak control plate is small, Good followability of channel box deformation, and good leak flow rate control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel assembly for a boiling water reactor equipped with a coolant leakage control mechanism, and more particularly to a leak flow control performance of a leak control plate. For those that have improved.

[0002]

2. Description of the Related Art Generally, a fuel assembly used in a boiling water nuclear reactor (BWR) is formed by bundling a plurality of fuel rods in a square lattice by a plurality of spacers arranged axially. And is held by an upper tie plate with a handle for suspension and a lower tie plate that forms an inflow path for the coolant from the lower part of the core.Furthermore, a channel box is fixed to the upper tie plate to fix the entire fuel assembly. It is a covered structure.

In such a fuel assembly, the internal pressure of the channel box becomes higher than the external pressure thereof during the operation of the reactor. Due to the relative pressure difference between the inside and outside of the channel box, the channel box expands and deforms outward, and the thermal effect and neutron irradiation effect of the high temperature and long-term operation of the reactor are added, and this expansion deformation tends to increase. Become.

The expanded deformation of the channel box as described above not only hinders the insertion of the control rods during the operation of the reactor, but also causes the coolant to leak more than necessary from the gap between the channel box and the lower tie plate. A sufficient cooling effect for the fuel rods cannot be obtained.

Therefore, at present, there is provided a leak control tool for constantly controlling the outflow of the coolant from the inside of the channel box due to the pressure difference between the inside and outside of the channel box. For example, the leak control plate 13 as shown in FIG. 4A is provided on each of the four side surfaces of the lower tie plate 12, and the leak flow rate is controlled by adjusting the distance between the channel box 11 and the lower tie plate 12. ing.

The leak control plate 13 has a plate thickness of 0.2 m.
It is made of a Ni-based alloy of about m and has a plurality of windows 14 for circulating the coolant and a plurality of slits 15 provided between the windows 14, as shown in the sectional view of FIG. In the vertical cross section along the axial direction of the assembly, the central portion has a substantially trapezoidal cross-sectional shape projecting toward the inner surface of the channel box 11, and a lower pocket provided on the lower side surface of the lower tie plate 12. After the lower edge portion is inserted into 18b, the upper edge portion is inserted into the upper pocket 18a.

Further, the upper edge portion is the leg portion 1 of the stopper plate 16.
6a is held by being loosely inserted into each window 14, and the stop plate 16 is fixed by a bolt 17. At this time, a predetermined space (clearance) is maintained between the ceiling portion in the upper pocket 18a and the upper end of the leak control plate 13. Leak control plate 13 mounted in this way
Is the upper and lower pockets (18a, 1a) of the lower tie plate 12.
8b) can move freely by the above clearance.

In the actual furnace, a pressure difference (internal pressure> external pressure) is generated inside and outside the channel box 11, causing bulge deformation in the channel box 11, and this bulge deformation amount increases due to creep deformation as the fuel burnup progresses.

When the channel box 11 swells due to such creep deformation, the main flow of the coolant leaks flowing out of the channel box 11 through the gap between the channel box 11 and the lower tie plate 12. The leak control plate 13 is taken in from the respective windows 14 of the leak control plate 13 to the back side thereof and urges the leak control plate 13 to the inner surface side of the channel box 11.

As a result, the leak control plate 13 follows the deformation of the channel box 11 and the channel box 1
1 The inner surface of the channel box 11 is deformed, and the central portion protruding toward the inner surface of the channel box 11 is pressed. Therefore, even if the interval between the lower tie plate 12 and the channel box 11 gradually increases, such a leak control plate By intervening, the coolant leakage flow rate to the outside of the channel box 11 is suppressed to an appropriate amount and is controlled to be constant.

[0011]

In the boiling water reactor fuel assembly provided with the leak control plate as described above, the pressure difference between the inside and the outside of the channel box is small, and the channel box from the rear side of the leak control plate is small. Even when the leak flow rate urged inward is small, it is desired to control the leak flow rate satisfactorily.

The present invention can control the leak flow rate well even when the pressure difference between the inside and the outside of the channel box is small, and has improved leak flow control performance of the leak control device for a boiling water reactor. The purpose is to obtain a fuel assembly.

[0013]

In order to achieve the above object, in the fuel assembly for a boiling water reactor according to the invention described in claim 1, a plurality of fuel cells are held in a square lattice array by a support lattice. A fuel bundle including fuel rods and water rods, an upper tie plate that suspends the upper end of the fuel bundle, a lower tie plate that supports the lower end of the fuel bundle, and the fuel that is suspended on the upper tie plate. It is attached to the outer surface of the lower tie plate so as to control the leak amount of the coolant from the gap between the channel box that surrounds the circumference of the bundle and the lower end of the channel box and the outer surface of the lower tie plate. In a fuel assembly for a boiling water nuclear reactor equipped with a leak control device, the leak control device occupies most of the width dimension of the flat side portion on the outer peripheral surface of the lower tie plate. In the vertical cross section along the axial direction of the assembly, the leak control plate has a cross-sectional shape in which the central portion projects toward the inner surface of the channel box in a substantially trapezoidal shape. The position of the center of gravity in the thickness direction is offset to the channel box side.

Further, in the boiling water nuclear reactor fuel assembly according to the present invention as defined in claim 2, in the boiling water nuclear reactor fuel assembly according to claim 1, the leak control plate is provided within the longitudinal section. The center of gravity position of the upper half part is closer to the channel box in the thickness direction than the center of gravity position of the lower half part.

Further, in the boiling water reactor fuel assembly according to the invention described in claim 3, in the boiling water reactor fuel assembly according to claim 1, the leak control plate is
In the cross-sectional shape, a portion having a wall thickness thicker than other portions is included above the central portion.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION In a fuel assembly for a boiling water reactor according to the present invention, a fuel bundle including a plurality of fuel rods and water rods held in a square lattice arrangement by a support lattice has an upper end portion as an upper portion. It is suspended by a tie plate, and the lower end is supported by a lower tie plate.On the outer peripheral surface of this lower tie plate, there is a gap between the lower end of the channel box and the outer peripheral surface of the lower tie plate. A leak control tool for controlling the leak flow rate of the coolant is installed.

In this leak control tool, the leak control plate, which occupies most of the width dimension of the flat side portion on the outer peripheral surface of the lower tie plate, has a substantially trapezoidal central portion in the longitudinal section along the axial direction of the assembly. It has a cross-sectional shape protruding toward the inner surface of the channel box, and the center of gravity in the thickness direction is offset toward the channel box side in the vertical cross section.

Normally, windows are alternately arranged in the width direction of the leak control plate along with slits, so that fuel combustion is performed in an actual furnace, a pressure difference between the inside and outside of the channel box is generated, and the channel box undergoes creep deformation. When it occurs, the leak flow of the coolant, which comes out of the fuel assembly and flows out through the gap between the channel box and the outer peripheral surface of the lower tie plate, is guided to the back side from the window of the leak control plate, and the leak control plate is discharged. Energize from the back side to the channel box side.

Due to this biasing, the leak control plate is deformed following the deformation of the channel box, and the central portion of the protrusion, which mainly has a substantially trapezoidal vertical cross section, is pressed against the inner surface of the channel box, and the leak flow rate is improved by closely adhering. It is controlled to be constant. Here, when the fuel burnup is small and the pressure difference between the inside and the outside of the channel box is relatively small, for example, 0.2 kg / cm ² or less, the leak flow rate of the coolant is small and the bias of the leak control plate toward the channel box side is small. Is also small.

However, according to the present invention, the above-mentioned leak is generated.
The center of gravity in the thickness direction in the vertical cross section of the control plate is offset to the channel box side, so the leak control plate itself tends to mechanically fall toward the channel box side, and even a small biasing force can easily Following the deformation, the leak flow rate can be controlled well even when the pressure difference between the inside and the outside of the channel box is small.

As described above, according to the present invention, the position of the center of gravity in the thickness direction in the vertical cross section of the leak control plate is biased to the channel box side and easily falls to the channel box side. By assuming that the center of gravity position of the upper half part of the leak control plate is inside the channel box side in the thickness direction than the center of gravity position of the lower half part,
With the lower end of the leak control plate as a fulcrum, the upper part can be easily tilted toward the channel box side. At this time, generally, a window for taking in the leak flow of the coolant is arranged near the upper shoulder of the substantially central trapezoid, and the leak flow from this window is easily taken in.

In general, the leak control plate is manufactured by a processing method such as press forming or rolling or cutting of Ni-based alloy material such as Inconel 718 by press forming or machining. Therefore, specifically, in order to obtain a leak control plate in which the position of the center of gravity in the thickness direction in the vertical cross section is offset to the channel box side, the molding shape may be preset in this manufacturing process.

For example, like the conventional leak control plate shown in FIGS. 1 (b) and 1 (c) having a vertical cross-sectional shape, the vertical cross-sectional shape is the same as the conventional one shown in FIG. 1 (a). The position of the center of gravity of the upper half part is changed by shaping the leak control plate whose center of gravity is almost symmetrical with respect to It is possible to obtain a leak control plate in which is closer to the channel box in the thickness direction than the center of gravity of the lower half.

Further, the center of gravity in the thickness direction in the vertical cross section is offset toward the channel box side by providing a portion in which the wall thickness is thicker than other portions above the central portion in the cross sectional shape. Alternatively, it is possible to obtain a leak control plate in which the position of the center of gravity of the upper half part is closer to the channel box in the thickness direction than the position of the center of gravity of the lower half part.

The leak control plate generally has a thickness of about 0.2 mm. For example, as shown in FIG. 1 (d), the thickness of the upper half of the central portion is smaller than that of the other portions. By increasing the thickness, the center of gravity of the upper half of the leak control plate can be located closer to the channel box in the thickness direction than the center of gravity of the lower half.

Further, as shown in FIG. 1 (e), the thickness of the central portion is made thicker than the upper and lower portions thereof, so that the position of the center of gravity in the thickness direction in the longitudinal section is offset toward the channel box side. Can be

Since the leak control plate is usually mounted by inserting the upper and lower end portions into the upper and lower pocket portions of the lower tie plate, the inner surface of the channel box is actually followed by the deformation of the channel box. Since it is the central protrusion that is pressed to the side, the center of gravity of the upper half is deformed in the thickness direction more than the center of gravity of the lower half by deforming the molding shape from the conventional one as described above. In case of manufacturing so that it is on the channel box side,
Although not limited to the shapes shown in (b) and (c),
It is desirable to consider that the protrusion height of the central portion and the shapes of the upper and lower end portions are basically the same as the conventional ones in consideration of the attachment to the lower tie plate and the distance from the channel box when attached.

When the wall thickness is made partially thicker than other portions, the thickness of the leak control plate itself required for the deformation following the deformation of the channel box does not become too thick so as not to be impaired. It is necessary to consider the setting of the wall thickness. For example, a partial thickness portion is 0.3 to 0.5 m for a thickness of a general leak control plate of about 0.2 mm.
It is desirable to be within the range of m.

Further, as a method of manufacturing such a leak control plate that is partially thicker than other portions, for example, as shown in FIG. 2A, a thickness corresponding to the thicker portion is used. The material cut out from the plate member X is processed as a leak control plate material x, or, as shown in FIG. 2B, a plate member Y having a normal thickness is formed in advance by a thickness corresponding to a difference in wall thickness. There is a method in which the other plate member y having the above is partially welded, and this is used as a raw material to be processed into a leak control plate.

[0030]

EXAMPLES Examples of the present invention will be shown below. As one embodiment of the present invention, in FIG. 3 (a), the thickness of the upper half of the central portion is made thicker than the other portions, and the center of gravity of the upper half is positioned in the thickness direction rather than the center of gravity of the lower half. 1 is a perspective view showing a schematic configuration of a lower tie plate portion of a boiling water reactor fuel assembly equipped with a leak control plate on the channel box side.

In the BWR fuel assembly of this embodiment, a plurality of fuel rods are bundled in a square lattice shape by a plurality of spacers (not shown) arranged in the axial direction, and suspended as in the conventional case. Held by an upper tie plate (not shown) provided with a handle for operation and a lower tie plate 2 forming an inflow path of the coolant from the lower part of the core, and further, a channel box 1 is fixed to the upper tie plate to fix the fuel assembly. The entire structure is covered.

Leak control plates 3 are provided on the flat sides (4 side surfaces) of the lower tie plate 2, and each leak control plate 3 is a conventional one shown in the sectional view of FIG. 4 (b). In the same manner as the above, the lower edge portion is inserted into the lower pocket 8b provided on the lower side surface of the lower tie plate 2, and then the upper edge portion is inserted into the upper pocket 8a. The legs 6 a of the stopper plate 6 are held by being loosely inserted into the window 4, and the stopper plate 6 is fixed by bolts 7.

At this time, a predetermined clearance (clearance) is maintained between the ceiling portion of the upper pocket 8a of the lower tie plate 2 and the upper end of the leak control plate 3. The leak control plate 3 attached in this way can move freely between the upper and lower pockets (8a, 8b) of the lower tie plate 2 by the amount of the above-mentioned clearance. A leak control tool for controlling the leak flow rate of the coolant flowing out of the box 1 is configured.

Each of the leak control plates 3 has a full width dimension of about 1
It is made of a Ni-based alloy of 10 mm, eight windows 4 of the same size are arranged in the width direction, and seven slits 5 are arranged between the windows 4 so as to alternate with the windows 4. In the leak control plate 3 of the present embodiment, as shown in the vertical sectional view along the axial direction of the assembly in FIG. 3B, the plate thickness of the upper half of the central portion 3a having a substantially trapezoidal vertical section is about 0. It is manufactured by rolling and cutting the plate thickness of other parts to 0.2 mm, and the center of gravity position of the upper half of the leak control plate 3 is closer to the channel box 1 side in the thickness direction than the center of gravity of the lower half. did.

As described above, in the leak control plate of this embodiment, the center of gravity of the upper half is located closer to the channel box 1 side in the thickness direction than the center of gravity of the lower half, and the upper half is easily tilted toward the channel box 1 side. Therefore, the pressure difference between the inside and outside of the channel box 1 is 0.2 kg / cm in the actual furnace.
^It is as small as ² or less, and therefore, even if the biasing force from the back side is relatively weak, it can be brought into good contact with the side surface of the channel box 1.

[0036]

As described above, the present invention makes it easier for the leak control plate to fall toward the channel box side because the position of the center of gravity in the thickness direction is offset to the channel box side in the longitudinal section. Even when the pressure difference between the inside and the outside is small, the leak control plate can be satisfactorily pressed against the inner surface of the channel box and the outflow of the coolant can be controlled.

[Brief description of drawings]

FIG. 1 shows an example of a leak control plate used in a fuel assembly for a boiling water reactor of the present invention. FIG. 1 (a) is a comparative example, and the center of gravity is almost in the thickness direction as in the conventional case. The schematic view showing the vertical cross-sectional shape along the axial direction of the assembly of the leak control plate in the center, (b) ~ (e) is a diagram showing the axial direction of the assembly of the leak control plate whose center of gravity is offset to the channel box side. It is a schematic diagram which shows the accompanying vertical cross-sectional shape.

2A and 2B are cross-sectional views illustrating an example of a method for manufacturing a leak control plate having a portion thicker than other portions used in the present invention.

3A and 3B are schematic configuration diagrams showing a fuel assembly for a boiling water reactor according to an embodiment of the present invention, wherein FIG. 3A is a perspective view of a lower tie plate portion, and FIG. It is an expanded sectional view of the mounting part of the leak control plate 3 shown in the figure.

FIG. 4 is a schematic configuration diagram showing an example of a conventional fuel assembly for a boiling water reactor, FIG. 4 (a) is a perspective view of a lower tie plate portion, and FIG. 4 (b) is a leak shown in FIG. 4 (a). FIG. 6 is an enlarged cross-sectional view of a mounting portion of a control plate 13.

[Explanation of symbols]

 1: Channel box 2: Lower tie plate 3: Leak control plate 3a: Central part of leak control plate 4: Window 5: Slit 6: Stop plate 6a: Leg part of stop plate 6 7: Bolt 8a: Upper pocket 8b: Bottom Pocket X: Thick plate member x: Leak control plate material (after cutting) Y: Plate member y: Plate member (for welding)

Claims (3)

[Claims] 1. A fuel bundle including a plurality of fuel rods and water rods held in a square lattice arrangement by a support lattice, an upper tie plate suspending an upper end portion of the fuel bundle, and a lower end portion of the fuel bundle. A lower tie plate supporting a portion, a channel box suspended from the upper tie plate and surrounding the periphery of the fuel bundle, and a gap between a lower end portion of the channel box and an outer peripheral surface of the lower tie plate. In a fuel assembly for a boiling water reactor equipped with a leak control tool mounted on an outer peripheral surface of a lower tie plate so as to control a leak amount of a coolant, the leak control tool is an outer peripheral surface of the lower tie plate. The leak control plate occupies most of the width dimension of the upper flat side portion, and the leak control plate has a substantially trapezoidal central portion in the vertical cross section along the axial direction of the assembly. And has a cross-sectional shape projecting toward the down channel box interior surface, the longitudinal plane that boiling water reactor fuel assembly, characterized in that the center of gravity position in the thickness direction is offset to the channel box side at. 2. The boiling water according to claim 1, wherein the center of gravity of the upper half of the leak control plate is closer to the channel box in the thickness direction than the center of gravity of the lower half of the vertical cross section. Type nuclear reactor fuel assembly. 3. The fuel for a boiling water reactor according to claim 1, wherein the leak control plate includes a portion having a wall thickness thicker than other portions above a central portion in the cross-sectional shape. Aggregation.