JP2958859B2 - Fuel assembly for boiling water reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coolant leak control mechanism provided in a fuel assembly for a boiling water reactor.

[0002]

2. Description of the Related Art Generally, a fuel assembly used in a boiling water reactor (BWR) has a structure as shown in FIG.
A plurality of fuel rods 13 are bundled in a square lattice by a plurality of spacers 14 arranged in the axial direction, and the upper tie plate 11 having a handle for suspension and the flow path of coolant from the lower part of the core are formed. Forming lower tie plate 15
And the channel box 12 is fixed to the upper tie plate 11 to cover the entire fuel assembly.

In such a fuel assembly, the internal pressure of the channel box 12 becomes higher than the external pressure during the operation of the reactor. The relative pressure difference generated inside and outside the channel box 12 causes the channel box 1
No. 2 expands outward, and the thermal effect of the high-temperature and long-time operation of the reactor and the effect of neutron irradiation are added, and this expanding deformation tends to increase.

[0004] The enlarged deformation of the channel box 12 as described above not only hinders the insertion of control rods during operation of the reactor, but also causes the coolant to leak more than necessary from the gap between the channel box 12 and the lower tie plate 15. Therefore, a sufficient cooling effect on the fuel rods cannot be obtained.

Therefore, at present, the channel box 1
In order to control the outflow of the coolant from the inside of the channel box 12 due to the pressure difference between the inside and outside of the container 2, leak control plates 16 as shown in FIG. The leak flow rate is controlled by adjusting the distance between the box 12 and the lower tie plate 15.

The leak control plate 16 has a plurality of windows 17a for flowing coolant and a plurality of slits 17b provided between the windows 17a, as shown in the sectional view of FIG. After the lower edge is inserted into the lower pocket 18b provided on the lower side surface of the lower tie plate 15, the upper edge is inserted into the upper pocket 18a.

Further, the upper edge is connected to the leg 1 of the stopper plate 19.
9b is retained by being loosely inserted into each window 17a, and the stopper plate 19 is fixed by bolts 20. At this time, the ceiling in the upper pocket 18a and the leak control plate 16
A predetermined interval (clearance) is maintained between the upper end and the upper end. The leak control plate 16 thus mounted
Are the upper and lower pockets (18a, 1) of the lower tie plate 15.
8b), it can move freely by the clearance.

Therefore, when a pressure difference (internal pressure> external pressure) is generated between the inside and outside of the channel box 12 in the actual furnace and the channel box 12 expands due to creep deformation, the channel box 12 is closed by a gap between the channel box 12 and the lower tie plate 15. A major part of the coolant leak flow which is about to flow out is taken in from the windows 17a of the leak control plate 16 to the rear side thereof and urges the leak control plate 16 toward the inner surface side of the channel box 12.

As a result, the leak control plate 16 deforms outward following the deformation of the channel box 12 and is pressed against the inner wall of the channel box 12, so that the distance between the lower tie plate 15 and the channel box 12 is increased. Instead, the flow rate of the coolant leaking out of the channel box 12 is controlled to be constant.

[0010]

However, in the conventional leak control plate as described above, when the pressure difference between the inside and outside of the channel box is relatively small, the follow-up deformation of the leak control plate with respect to the bulging deformation of the channel box becomes small. .

[0011] This is because the swelling deformation of the channel box is relatively small, and the leakage flow rate of the coolant flowing out between the inner wall of the channel box and the lower tie plate is generally small. This is because the leak flow rate introduced into the rear side is also small, and a sufficient biasing force for sufficiently deforming the leak control plate to follow the inner wall side of the channel box from the rear side cannot be obtained.

Therefore, when the pressure difference between the inside and outside of the channel box is small, the cooling leak control plate cannot satisfactorily deform to follow the inner wall side of the channel box, and the control of the coolant leak flow rate becomes insufficient. This causes a problem that the coolant flows out of the channel box more than necessary.

In view of the above-mentioned problems, the present invention provides a leak control plate that follows the swelling deformation of the channel box even when the pressure difference between the inside and outside of the channel box is small, so that good leak flow control can be performed. An object of the present invention is to obtain a leak control mechanism of a fuel assembly for a boiling water reactor.

[0014]

According to the first aspect of the present invention, a fuel assembly for a boiling water reactor includes a plurality of fuel rods and water rods held in a square lattice by a support lattice. A fuel bundle, an upper tie plate that suspends an upper end of the fuel bundle, a lower tie plate that supports a lower end of the fuel bundle, and a channel that is suspended by the upper tie plate and surrounds the fuel bundle. A leak provided on an outer peripheral surface of the lower tie plate so as to reduce a gap amount of a box and a lower end portion of the channel box and an outer peripheral surface of the lower tie plate in accordance with an increase in internal pressure of the channel box. And a control unit, wherein the leak control unit is a side excluding a corner on an outer peripheral surface of the lower tie plate. In the corner portion of the outer peripheral surface of the lower tie plate, the leak flow of the coolant from inside the channel box is guided to the back of the leak control device, and the leak control device is attached to the inner side of the channel box. A groove for energizing is provided.

[0015]

According to the present invention, a leak control device is provided on a side of a fuel assembly for a boiling water reactor except for a corner on an outer peripheral surface of a lower tie plate, and a groove is formed on a corner of an outer peripheral surface of the lower tie plate. It is provided. The groove guides the leak flow of the coolant from inside the channel box to the back surface of the leak control device, and can urge the leak control device toward the inner surface of the channel box.

FIG. 2B is a cross-sectional view of the fuel assembly in a direction perpendicular to the axial direction. As shown in FIG.
Looking at the gap between the channel box 12 and the inner wall of the channel box 12, when the bulging deformation of the channel box 12 is small, the gap is generally smaller than the distance d at the outer peripheral side (here, four sides) of the lower tie plate 15. The distance D at the corner of the outer peripheral surface of the lower tie plate 15 is large.

Therefore, in such a fuel assembly,
Of the coolant leak flow leaking from inside the fuel assembly and flowing into the gap between the channel box and the lower tie plate, most of the coolant leaks flows out from the gap having the corner interval D.

Therefore, in the present invention, since the main coolant leak flow which is going to flow out from the gap at the corner portion can be guided to the back side of the leak control plate by the groove, the pressure difference between the inside and outside of the channel box is small. Even in this case, the leak control plate is urged from the back side by the guided coolant leak flow, and the urging allows the deformation of the leak control plate to sufficiently follow the relatively small bulging deformation of the channel box. Thus, it is possible to control the leak flow rate.

The shape of the groove provided at the corner of the outer peripheral surface of the lower tie plate according to the present invention is, for example, a longitudinal groove whose longitudinal direction is provided along the axial direction of the fuel assembly, and a groove extending from the lower end of the longitudinal groove. A substantially inverted T-shaped groove formed by a lateral groove provided substantially toward the center of the leak control plate located on both sides of the corner portion is conceivable.

Of course, the groove of the present invention is not limited to this inverted T-shape. Normally, the leak control plate is
As can be seen from the side sectional view of FIG. 2, the central portion is fitted in a convexly bent state, so that the convex central portion forms a space with respect to the lower tie plate surface, and Both sides are open. Therefore, if a groove is formed toward this opening, the coolant leak flow guided by this groove is easily introduced into the space on the back side from both sides of the leak control plate.

The grooves provided at the corners are, of course, located above the lower end of the channel box. Even if the fuel rods expand during operation and combustion in an actual furnace and the channel box is lifted upward, the channel is always raised. What must be in the position covered by the box
It is the same as a normal leak control plate.

Further, in the groove portion of the corner portion, the distance from the channel box inner wall becomes larger than that of the conventional one by the provision of the groove, but the portion below the groove of the corner portion becomes smaller than the channel box inner wall. If the distance is the same as the conventional one, that is, if the distance is equivalent to the distance D in FIG. 2B, the problem that the entire coolant leak flow rate increases can be avoided.

[0023]

The present invention will be described below in detail with reference to examples. FIG. 1 is a view showing a schematic configuration of a lower tie plate portion of a fuel assembly according to an embodiment of the present invention. Here, a case where an inverted T-shaped groove is provided at each corner will be described.

As shown in FIG. 1A, the fuel assembly according to the present embodiment has a plurality of fuel rods 3 bundled in a square lattice by a plurality of spacers (not shown) arranged in the axial direction. And is held by an upper tie plate (not shown) having a handle for suspension and a lower tie plate 5 forming a flow path of a coolant from the lower part of the core. Further, the channel box 2 is fixed to the upper tie plate. Thus, the entire fuel assembly is covered.

A leak control plate 6 is provided on each side of the outer surface of the lower tie plate 5. These leak control plates 6 are provided with a plurality of windows 7a for distributing the coolant and a plurality of slits 7b provided between the windows 7a, and have a shape in which a central portion is bent in a convex shape. .

Such a leak control plate 6 is shown in FIG.
After the lower edge is inserted into the lower pocket (not shown) provided on the lower surface of the lower tie plate 5, the upper edge is inserted into the upper pocket (not shown). Is inserted on the outer peripheral surface of the lower tie plate 5.

Further, the upper edge is held by loosely inserting the legs of the stopper plate 9 into the windows 7a, and the stopper plate 9 is fixed by bolts 10. At this time, a predetermined interval (clearance) is maintained between the ceiling in the upper pocket and the upper end of the leak control plate 6. The leak control plate 6 attached in this manner can freely move between the upper and lower pockets of the lower tie plate 5 by the clearance.

At each corner of the lower tie plate 5,
An inverted T-shaped groove 8 is formed. This groove 8 corresponds to FIG.
As shown in the partial view of (b), a vertical groove 8a extending along the axial direction of the fuel assembly to a position substantially corresponding to the center of the leak control plate 6, and a left and right direction from the lower end of the vertical groove 8a; That is, it is composed of the lateral groove 8b extending in a direction perpendicular to the axial direction. Therefore, the open end of each lateral groove 8b is directed toward both side openings S of the space formed by the convex central portion of the leak control plate 6.

The case where the fuel assembly having the grooves provided at the respective corners of the lower tie plate 5 is used in an actual furnace will be described below. When the operation of the reactor is started, the internal pressure of the channel box 2 becomes higher than its external pressure. Due to the relative pressure difference between the inside and outside of the channel box 2, the channel box 2 starts to expand outward and deform.

The coolant leaking from the inside of the fuel assembly flows out of the channel box 2 through a gap between the inner wall of the channel box 2 bulging outward and deforming and the outer peripheral surface of the lower tie plate 5. Some of the leak flow entering the gap between the inner wall of the channel box 2 and the outer peripheral surface of the lower tie plate 5 is taken into the back side of the leak control plate 6 from each window 7 a of the leak control plate 6.

While the pressure difference between the inside and outside of the channel box 2 is small, the amount of deformation to the outside of the channel box 2 is small. Is not enough to be able to be urged from the rear side so as to follow the change.

However, in the present embodiment, most of the leak flows that are going to flow out between the inner wall of the channel box 2 and the outer peripheral surface of the lower tie plate 5 are generated at each corner of the lower tie plate 5. It is guided from the vertical groove 8a of the groove 8 to the horizontal groove 8b, and is introduced from the left and right ends of the horizontal groove 8b to the rear side of the leak control plate 6 through both side openings S of the convex central space of each leak control plate 6.

The leak control plate 6 is urged from the rear side by the leak flow introduced from the groove 8, and deforms outward following the bulging deformation of the channel box 2, and the inside of the lower tie plate 5 and the inside of the channel box 2. The gap distance from the wall surface is well adjusted, and the overall coolant leak rate can be appropriately controlled.

In this embodiment, the provision of the groove 8 increases the distance between the channel box 2 and the inner wall of the channel box 2 at the corner where the groove 8 is provided. As shown in the partial side view of FIG. 3 (c), the distance L between each corner portion and the inner wall of the channel box 2 below the groove 8 is defined as the distance when such a groove is not provided in the corner portion. In other words, by setting the same interval (corresponding to the interval D in FIG. 2B) as that of the corner portion of the lower tie plate of the conventional fuel assembly, the total leak flow rate outside the channel box 2 is reduced. The design was designed to avoid the problem of unnecessarily increasing.

Further, when the effect of thermal and neutron irradiation by the high-temperature and long-time operation of the nuclear reactor is added and the expansion deformation of the channel box 2 is increased, the inner wall of the channel box 2 and the lower tie plate 5 The flow rate of the coolant leaking from the gap with the outer peripheral surface tends to increase, but at this time, the leak flow guided to the groove 8 is taken into the back side of the leak control plate 6, and It is urged from the side to satisfactorily deform following the large bulging deformation of the channel box 2, thereby suppressing an increase in leak flow rate.

As described above, when the relative pressure difference between the inside and outside of the channel box 2 is large and the swelling deformation is large,
When the action of the leak control plate 6 is urged by the groove 8, the coolant leak flow rate from the inside of the channel box 2 is favorably controlled.

In the above embodiment, the grooves provided at the corners of the lower tie plate are formed in an inverted T shape.
The groove according to the present invention may have any shape as long as the coolant leak flow flowing into the gap between the corner portion of the lower tie plate and the inner wall of the channel box can be introduced to the back side of the leak control plate. .

[0038]

As described above, according to the present invention, a groove is provided at a corner of a lower tie plate provided with a leak control plate on the side, and the groove leaks from inside the fuel assembly to form an inner wall of the channel box. By introducing the leak flow, which flows out of the gap between the inner wall of the channel box at the corner portion, of the coolant leak flow flowing into the gap with the outer peripheral surface of the lower tie plate to the rear side of the leak control plate, Even if the pressure difference between the inside and outside of the box is small and the bulging deformation is small, the leak control plate can be urged from the back side to follow and deform well, and the coolant always flows out of the channel box during actual furnace operation. There is an effect that the leak flow rate can be controlled.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a schematic configuration near a lower tie plate of a fuel assembly according to one embodiment of the present invention, (a) is a perspective view of a lower tie plate portion including a leak control mechanism,
(B) is an enlarged view of a corner portion of the lower tie plate shown in (a), and (c) is a schematic side view near the lower tie plate corner portion.

FIG. 2 is a schematic configuration diagram showing an example of a fuel assembly according to the related art, wherein (a) is a cross-sectional view along the axial direction of the fuel assembly, and (b) is an AA ′ position in the cross-sectional view of (a). FIG. 3 is a cross-sectional view along a direction orthogonal to the axial direction of the fuel assembly in FIG.

3A and 3B are explanatory views showing a schematic configuration near a lower tie plate of a conventional fuel assembly, wherein FIG. 3A is a perspective view of a lower tie plate portion including a leak control mechanism, and FIG. It is sectional drawing which shows a structure.

[Explanation of symbols]

 11: Upper tie plate 2, 12: Channel box 3, 13: Fuel rod 14: Spacer 5, 15: Lower tie plate 6, 16: Leak control plate 7a, 17a: Window 7b, 17b: Slit 8: Groove 8a: Vertical Groove 8b: Lateral groove 18a: Upper pocket 18b: Lower pocket 9, 19: Stop plate 19b: Leg (of stop plate) 10, 20: Bolt

Claims (1)

(57) [Claims] 1. A fuel bundle including a plurality of fuel rods and water rods held in a square lattice by a support lattice, an upper tie plate for suspending an upper end of the fuel bundle, and a lower end of the fuel bundle. A lower tie plate for supporting a portion, a channel box suspended around the upper tie plate and surrounding the fuel bundle, and a gap at an overlapping portion between a lower end portion of the channel box and an outer peripheral surface of the lower tie plate. A leak control device provided on the outer peripheral surface of the lower tie plate so as to reduce the amount in accordance with an increase in the internal pressure of the channel box, a fuel assembly for a boiling water reactor, comprising: The lower tie plate is provided at a side portion excluding a corner portion on the outer peripheral surface, and the corner portion of the outer peripheral surface of the lower tie plate has a channel. A boiling water reactor provided with a groove for guiding a leak flow of the coolant from inside the leak box to a rear surface of the leak control tool and urging the leak control tool toward the inner surface side of the channel box. Fuel assembly.