JPH06138271A - Fuel assembly for boiling water reactor - Google Patents

Abstract

PURPOSE:To operate a reactor core of enhanced fuel output and to prevent creep deformation of a water channel wall due to the difference between inner and outer pressures CONSTITUTION:Flow trippers 2 are mounted at proper intervals to the overall length of the wall surface of a rectangular water channel 1 provided within a fuel assembly 10. A coolant flowing on the wall surface of the channel is deviated toward a fuel rod 11 adjoining to the wall surface of the channel by the flow trippers 2 serving as protruding portions, so as to enhance the cooling efficiency of the fuel rod and to enable the operation of a reactor to enhance the fuel output and to reduce the flow rate of coolant Also, creep deformation due to the difference between inner and outer pressures can be prevented by increasing the strength of the wall surface of the channel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention In the present invention, a projection is provided as a coolant flow tripper (flow turning means) on a wall surface of a water channel of a fuel assembly for a boiling water reactor (hereinafter abbreviated as BWR). The present invention relates to a BWR fuel assembly.

[0002]

2. Description of the Related Art In a BWR fuel assembly, conventionally, one or two fuel rods in the central portion thereof are omitted, and instead, a water rod having substantially the same outer diameter as that of the fuel rod is loaded, and the inside of this water rod is loaded. By allowing the coolant to pass through, the neutron moderating effect of the coolant is enhanced, the nuclear fuel enrichment is reduced in the peripheral fuel rods, and the nuclear fuel enrichment is increased in the central fuel rods. Then, the output distribution in the horizontal direction is made uniform. However, since the conventional water rod has a small diameter, the output distribution cannot be sufficiently made uniform, and there is a complexity in that a difference in the enrichment of the nuclear fuel must be set between the peripheral portion and the central portion. Therefore, a square water channel with a side length of about 3.5 times the fuel rod diameter and a storage area equivalent to about 9 fuel rods was placed in the center to make the power distribution uniform and slow down neutrons. A fuel assembly for BWR shown in FIG. 5 that improves the effect has been proposed. In the figure, 1 is a water channel, 10 is a fuel assembly, 1
1 is a fuel rod, 12 is a spacer, 13 is an upper tie plate, and 14 is a lower tie plate. Further, as the burnup of fuel becomes higher, it is required to increase the fuel output and to improve the flexibility of the reactor operation such as the operation in which the flow rate of the coolant is reduced. In addition, in the structure using square water channels, when the coolant stays in the furnace for a long time, creep deformation due to the pressure difference between the inside and outside tends to occur, and the wall surface of the water channel bulges outward and engages with the spacer. This is not preferable, and means for preventing these are required. It is known that this deformation is larger in the upper and lower parts than in the central part of the water channel.

[0003]

SUMMARY OF THE INVENTION According to the present invention, the coolant flowing on the water channel wall surface of the fuel assembly for BWR is diverted toward the fuel rod adjacent to the water channel wall to improve the cooling efficiency of the fuel rod. It is an object of the present invention to enable the operation of increasing the output of or the operation of decreasing the flow rate of the coolant, further improve the strength of the water channel, and prevent the creep deformation and the like due to the difference in internal and external pressures.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, and the protrusions are formed at appropriate intervals over the entire length of the wall surface of the rectangular water channel provided in the fuel assembly. That is, I decided to attach a flow tripper. Moreover, the shape increases in height from the lower tie plate toward the upper tie plate, and the inclined portion is slightly curved toward the center of the water channel.

[0005]

By attaching the flow tripper to the square water channel, the coolant flowing on the wall surface of the water channel, which is a non-heating element, is diverted toward the fuel rod adjacent to the wall surface of the water channel to improve the cooling efficiency of the fuel rod. It is possible to increase the fuel output and increase the fuel output, or to reduce the coolant flow rate, and further improve the strength of the wall surface of the water channel to prevent creep deformation and the like due to the internal / external pressure difference.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a simplified schematic view of a BWR fuel assembly according to the present invention, in which a flow tripper 2 is attached to a wall surface of a water channel 1 at appropriate intervals.

2 to 4 are BWRs according to the present invention.
It is explanatory drawing of the shape of the flow tripper attached to the water channel wall surface of the fuel assembly for vehicles, and its attachment method. The embodiment of FIG. 2 shows the shape of the flow tripper when attached by welding. 2a is a top view,
2b is a front view and 2c is a side view. In this case, since the material of the flow tripper is weldable, the same material as the channel box, that is, Zircaloy 4 is desirable. In the embodiment of FIG. 3, a flow tripper is provided by cutting out the wall surface of a water channel, and FIG. 3 is a vertical cross-sectional explanatory view, in which 1 is a water channel and 2 is a flow tripper. Figure 4
The embodiment of FIG. 1 is a longitudinal sectional view of a flow tripper provided by stamping on the wall surface of a water channel.
Is a water channel, and 2 is a flow tripper.

[0008]

EFFECTS OF THE INVENTION The effects of the present invention can be achieved by installing a flow tripper, (1) operation of a reactor with increased fuel output, and (2) prevention of creep deformation due to pressure difference between inside and outside of water channel wall. Become.

[Brief description of drawings]

FIG. 1 is an explanatory view of an embodiment in which a flow tripper is attached to a wall surface of a water channel of a BWR fuel assembly.

FIG. 2 is an explanatory view of an embodiment of the shape of a flow tripper attached to the wall surface of a water channel by welding.

FIG. 3 is a sectional view of the shape of an embodiment of a flow tripper by carving out the wall surface of a water channel.

FIG. 4 is a sectional view of the shape of an embodiment of a flow tripper by punching a wall surface of a water channel.

FIG. 5 is a schematic cross-sectional explanatory view of a conventional BWR fuel assembly.

[Explanation of symbols]

 1 Water Channel 2 Flow Tripper 2a Top View of Flow Tripper by Welding 2b Front View of Flow Tripper by Welding 2c Side View of Flow Tripper by Welding 10 Fuel Assembly 11 Fuel Rods 12 Spacer 13 Upper Tie Plate 14 Lower Tie Plate

Claims (1)

[Claims] 1. A water channel located in the central portion of a fuel assembly for a boiling water reactor, the shape of which increases from the lower tie plate toward the upper tie plate, and the sloped portion is the center of the water channel. A fuel assembly for a boiling water reactor, comprising a plurality of slightly curved flow trippers attached to a wall surface.