JP2002062392A - Lower tie-plate of fuel assembly for boiling water reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lower tie-plate of fuel assembly for a boiling water reactor provided with a foreign article trapping means capable of properly preventing invasion of coolant-mixed foreign articles into fuel rod region, easily responding to change of fuel rod array and ensuring always sufficient coolant flow rate. SOLUTION: A slab foreign article trapping filter member is constituted by combining in parallel face to face state with a specific interval or in contact with a first filter plate arranged upstream the coolant flow in the lower tie-plate in a fuel assembly for a boiling water reactor and formed by a plurality of slit opening by bridging a multitude of metal thin plate having a predetermined width and thickness over a square frame member in parallel with a specific intervals and a second filter plate arranged downstream of the first filter plate and constituted by providing the metal plate with a multitude of thin holes. These are installed in a lower position than an upper support plate, not in contact, supporting fuel rod lower end plugs.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lower tie plate of a fuel assembly for a boiling water reactor, and more particularly, to a lower tie plate having a filter means for trapping foreign matter and filtering a coolant. Things.

[0002]

2. Description of the Related Art A typical fuel assembly of a boiling water reactor (BWR) has a plurality of fuel rods bundled in a square lattice array, and upper and lower ends are supported by an upper tie plate and a lower tie plate. In this state, it is housed in a rectangular tubular channel box. Bundles of fuel rods usually contain a small number of water tubes consisting of hollow tubes in the center, and are spaced from each other by spacer grids arranged at predetermined intervals at a plurality of locations between the upper and lower tie plates, forming a square lattice shape. Supported by the array.

After these fuel assemblies have been loaded into the reactor core, coolant is introduced from the coolant inlet at the lower end of the lower tie plate, flows between the fuel rods, and flows out from above the upper tie plate. Thereby, it circulates in the reactor as the primary coolant of the reactor. However, during such coolant circulation, foreign matter such as metal chips mixed into the plant flows into the channel box together with the coolant, and particularly fine foreign matter enters the gap between the spacer grid and the fuel rods, and the fuel rods are scattered. Causing damage to the surface due to abnormal wear,
The danger of fuel damage is considered. Therefore, it has been considered that a filter is provided in the lower tie plate to capture foreign matter mixed in the coolant and prevent the coolant from entering the fuel rod side.

For example, Japanese Unexamined Patent Publication No. 11-23763 discloses that a grid portion, which is a support portion of each fuel rod lower end plug on an upper portion of a lower tie plate, is formed into a flat plate shape instead of a conventional grid shape. A structure in which pores are also provided in a region around the fuel rod insertion hole which was the lattice portion of the above is disclosed.

[0005] However, such a method of integrally providing the grid portion of the lower tie plate and the foreign matter capturing portion is effective for capturing foreign matter larger than the pore diameter, but is trapped between the fuel rod and the spacer. Fine wire-like foreign matter, which is considered to be the cause of fretting, may be drawn into the pores while moving on the surface of this flat plate and immediately enter the fuel rod area. There is. Also, since the fuel rod lower end plug support portion and the foreign matter catching portion are integrated, it is not possible to significantly increase the total coolant flow path area and suppress the increase in pressure loss by taking into account the strength of the flat plate. It seems difficult to some extent.

Japanese Patent Application Laid-Open No. 8-240678 discloses a device provided with a foreign matter capturing mechanism comprising a member having a large number of openings in a flow path formed by a boss and a web while keeping the grid of the grid portion. Is disclosed. However, in this case, each time the fuel rod arrangement is changed, it is necessary to recreate the foreign matter trapping part, and since the foreign matter trapping part further enters the flow path formed by the boss and the web, the coolant flow in the grid part is reduced. This causes a problem that the pressure loss increases. In the future, as the number of fuel rods increases as the fuel assemblies become more prone to burning, the cross-sectional area of the flow path will further decrease, so the pressure loss will further increase and cooling to the fuel rod area will occur. Material may not be supplied sufficiently, and the integrity of the fuel body may be impaired.

Further, Japanese Patent Application Laid-Open No. H8-240677 discloses an arrangement in which two plates are combined immediately below a lower tie plate grid portion to form a grid-like flow path. However, this method has an advantage that the structure itself of the lattice flow path does not increase the pressure loss of the coolant flow, but at least the plate on the downstream side has a hole for inserting the lower end plug of the fuel rod, As a result, it is installed so as to be in contact with the lower surface of the grid portion. In the same manner as disclosed in the above-mentioned JP-A-8-240678, a foreign matter catching portion is provided immediately below a flow path formed by ribs and a web. As a result, the pressure loss in this portion increases, and the coolant is not sufficiently supplied to the fuel rod region, which may impair the soundness of the fuel body.

[0008]

In the lower tie plate of the conventional fuel assembly for a boiling water reactor, the foreign matter trapping mechanism provided in the lower tie plate is not limited to the above example. The fuel rod is provided integrally with or in contact with the fuel rod support portion, and its structure and arrangement are governed by the fuel rod arrangement. Therefore, in the future, the burnup will further increase, and the number of fuel rods in the fuel assembly will increase. Each time, the fuel rod lower end plug support must be rebuilt,
As the number of fuel rods increases, the coolant flow path formed by the boss and the web becomes smaller, and it becomes difficult to adjust the flow path resistance to a required value.

Therefore, while ensuring a sufficient flow rate of the coolant, foreign matters mixed in the coolant are satisfactorily captured, and the foreign matters are prevented from entering the fuel rod region and damaging the fuel rod by fretting or the like. It is considered that an excellent foreign matter trapping mechanism that can perform the above-mentioned operation and can easily cope with an increase in the arrangement of the fuel rods has not yet been realized.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to prevent foreign matter mixed in a coolant from entering a fuel rod region, to easily cope with a change in fuel rod arrangement, and to always provide a sufficient coolant flow rate. It is an object of the present invention to provide a lower tie plate of a fuel assembly for a boiling water reactor provided with foreign matter trapping means capable of securing pressure loss and easily adjusting a pressure loss amount.

[0011]

In order to achieve the above object, a lower tie plate of a fuel assembly for a boiling water reactor according to the first aspect of the present invention comprises a plurality of fuel rods having a predetermined square lattice. In a lower tie plate of a boiling water reactor fuel assembly supported at both upper and lower ends by an upper tie plate and a lower tie plate as a bundle in a shape arrangement, a flat plate-like foreign matter trapping filter member is provided under the fuel rod. Built in a lower position not in contact with the upper support plate supporting the end plug, the foreign matter trapping filter member is disposed on the upstream side of the coolant flow in the lower tie plate, and is previously mounted on a substantially square frame member. A first filter plate in which a plurality of rows of slit-shaped openings are formed by laying a number of thin metal plates having a predetermined width and thickness in parallel at predetermined intervals, and the first filter; Disposed downstream from the filter plate, a second filter plate formed by providing a large number of pores in the metal plate, in which are combined in parallel to face each other with a predetermined interval.

[0012] The lower tie plate of the fuel assembly for a boiling water reactor according to the present invention according to the second aspect is the lower tie plate of the fuel assembly for a boiling water reactor according to the first aspect. The built-in position of the filter
The coolant flow path cross-sectional area in the lower tie plate is located at a maximum position.

[0013] The lower tie plate of the fuel assembly for a boiling water reactor according to the third aspect of the present invention may be configured such that a large number of fuel rods are bundled in a predetermined square lattice arrangement as an upper tie plate and a lower tie plate. In the lower tie plate of the boiling water reactor fuel assembly supported at the upper and lower ends by the rate, the plate-like foreign matter trapping filter member is not in contact with the upper support plate supporting the lower end plug of the fuel rod. Built in a lower position, the foreign matter trapping filter member is disposed on the upstream side of the coolant flow in the lower tie plate, and has a plurality of frames having a predetermined width and thickness in a substantially square frame member. A first filter plate in which a plurality of rows of slit-shaped openings are formed by horizontally laying thin metal plates in parallel at a predetermined interval; and a first filter plate disposed downstream from the first filter plate. A second filter plate formed by providing a large number of pores in the metal plate, in which are combined face-to-face state in close contact with each other.

Further, the lower tie plate of the fuel assembly for a boiling water reactor according to the invention described in claim 4 is provided in claim 3.
In the lower tie plate of the boiling water reactor fuel assembly according to the above, the built-in position of the foreign matter capturing filter member, the coolant flow path cross-sectional area in the lower tie plate is a position that is the maximum. It is a feature.

In the lower tie plate of the present invention, a plurality of thin metal plates are horizontally arranged at predetermined intervals on a substantially rectangular frame member as a filter member for capturing foreign matter, which is disposed on the upstream side in the lower tie plate. A first filter plate in which a plurality of rows of slit-shaped openings are formed, and a metal plate disposed downstream of the first filter plate with a large number of pores. Since the foreign matter capturing filter member configured by combining with the second filter plate is built in a lower position not in contact with the upper support plate supporting the fuel rod lower end plug of the lower tie plate, The foreign substances flowing into the lower tie plate together with the coolant are supplied to the slit-shaped opening of the first filter plate, then to the gap between the first and second filter plates, and to the second filter plate. Pores of the filter plate, and, because it is captured in a sequential flow path of narrowing filter arrangement, intrusion into the fuel rod region is very difficult.

Further, according to the filter member structure of the present invention, even if foreign matter is captured on the upstream surface of the first filter plate and the filter is partially blocked, the coolant bypasses the filter and bypasses the first filter plate. 2 can flow into the filter plate side, and flow almost smoothly through the pores to the fuel rod side, so that an increase in coolant flow pressure loss due to clogging can be prevented.

Further, the filter member for trapping foreign matter according to the present invention is disposed at a lower position in the lower tie plate that does not contact the upper support plate, and the dimensional and strength restrictions due to the fuel rod arrangement of the upper support plate are directly affected. The pressure loss at the lower tie plate can be easily adjusted only by increasing or decreasing the width and interval of the metal thin plate of the first filter plate and the diameter and number of the pores of the second filter plate. Even when the grid shape of the upper support plate, that is, the fuel rod arrangement is changed, the lower tie plate can be easily adjusted to have a predetermined pressure loss.

[0018] The pressure loss is also affected by the distance between the first filter plate and the second filter plate. That is, if the distance between the two filter plates is increased, the pressure loss decreases, and if the filter plates are brought into close contact with each other, the pressure loss increases. Therefore, the pressure loss can be adjusted by adjusting the distance between the two plates.

As described above, in the case where the pressure loss is also adjusted by adjusting the distance between the two plates, it is necessary to set the pressure loss higher. They may be closely contacted without any space. At this time, the foreign matter capturing function due to the gap between the two plates as described above is lost, but in the present invention, a high foreign matter capturing performance is exhibited by the combination of the first filter plate and the second filter plate. Absent.

The position of the foreign matter trapping filter member in the present invention may be any lower position not in contact with the upper support plate in the lower tie plate as described above. In consideration of the above, it is usually desirable to arrange the lower tie plate flow path at the position having the largest flow path cross-sectional area.

Such a foreign matter trapping filter member may be manufactured separately from the lower tie plate and then incorporated into the lower tie plate later. Therefore, it not only has a high foreign matter trapping performance, but also can be easily manufactured with high accuracy without being affected by the fuel rod support portion. As described above, the design can be easily changed and adjusted in response to the change in the predetermined pressure loss. This can increase the degree of freedom of design in increasing the burnup of the fuel assembly, and can realize the development of a new foreign matter trapping mechanism at low cost.

Further, the shape of the pores of the second filter plate is not limited to a general circular or elliptical shape, but various shapes such as a polygon, a one-character slit shape, or a cross slit shape can be adopted. In addition, such a second filter plate has a simple configuration in which a through hole is formed as if a metal plate member is punched out. However, the present invention is not limited to this, and a substantially rectangular frame is formed similarly to the first filter plate. A member having a slit-like opening formed by bridging a metal thin plate horizontally may be used. In this case, if the slits are combined so that the longitudinal directions thereof are orthogonal to each other, and a mesh-like pore is formed by the grid-like overlap of both plates, high foreign matter capturing performance can be obtained.

However, from the viewpoint of foreign matter capturing performance, the pores of the second filter plate are preferably smaller than the slit-shaped apertures of the first filter plate. Therefore, the second filter plate itself has a large number of pores, which are smaller than the slit-shaped apertures of the first filter plate, as compared with the case where the first and second filter plates overlap to form a pore-shaped flow path. Preferably, it has pores. Therefore, when the second filter plate is constituted by a plurality of thin metal plates arranged horizontally, the metal thin plates may be arranged horizontally in a grid to form a network-like flow path.

As a method for incorporating the foreign matter trapping filter member of the present invention below the lower tie plate fuel rod support plate, for example, an opening window is formed at a predetermined height position on the side wall surface of the lower tie plate. Inserting the pre-assembled foreign matter trapping filter member from the opening window, sliding it into the inside, fixing it by welding or the like, or cutting the lower tie plate up and down at a predetermined height position, or It is convenient to manufacture the upper and lower parts separately, and fix the three members integrally by welding or the like with the filter member interposed between the upper and lower parts.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As one embodiment of the present invention, a combination of a first filter plate having a plurality of rows of slit-shaped apertures and a second filter plate having a large number of circular pores is provided. FIG. 1 shows a lower plate of a fuel assembly for a boiling water reactor incorporating a foreign matter trapping filter member constituted by the above. FIG. 1A is a schematic configuration diagram of a lower tie plate of the present embodiment, and FIG. 1B is a schematic plan view of a foreign matter capturing filter member in the lower tie plate viewed from an upstream side of a coolant flow. .

The lower tie plate 1 according to this embodiment is:
The foreign matter trapping filter member 3 is inserted below the upper support plate 2 supporting the fuel rod end plug, between the upright side walls having the largest coolant flow path cross-sectional area in the lower tie plate. In this foreign matter capturing filter member 3, the first filter plate 4 arranged on the upstream side and the second filter plate 7 arranged on the downstream side are combined in a mutually facing state with a slight interval X therebetween. Things.

The first filter plate 4 has a plurality of rows of slits formed by laying a large number of thin metal plates 5 having a predetermined width and thickness on a substantially square frame member in parallel at predetermined intervals. The opening 7 is formed, and the second
The filter plate 7 is a metal plate in which pores 8 are formed as a large number of through holes.

[0028] Foreign matter trapping filter member 3 of the present embodiment.
Is the opening area of the pores 8 of the second filter plate 7,
The pressure loss is increased by making the opening area of the slit-shaped opening 7 of the first filter plate 4 significantly smaller than that of the first filter plate 4 and by capturing foreign substances stepwise according to the size thereof. And has a high foreign matter trapping property.

Hereinafter, the situation of foreign matter capturing by the foreign matter capturing filter member 3 in a stepwise manner will be described. Here, for simplicity of description, a case where n slit holes 6 of the first filter plate 4 are formed in n columns and n ² pores 8 of the second filter plate 7 are formed in n rows and n columns. Show.
The distance between the first filter plate 4 and the second filter plate 7 is determined by the width of the slit-shaped opening 6 (the thin metal plate 5).
(The width of the gap between them).

First, as shown in FIG. 2, in the case of a foreign substance 11 larger than the width of each channel of the slit-shaped opening 6, the foreign substance 11 is captured by the surface portion of the first filter plate 4 on the upstream side. Since the slit-shaped opening 8 has an elongated shape, even if a part of the flow path is blocked by the foreign matter 11,
The coolant bypasses the foreign matter 11 and flows into the second filter plate 4 on the downstream side, and can smoothly flow into the entire pores 8, so that the filter member does not cause an increase in pressure loss due to clogging. .

Next, as shown in FIG. 3, foreign matter 12 that is narrower than the flow path width of the slit-shaped opening 6 and larger than the gap width X between the first filter plate 4 and the second filter plate 7 is removed. In this case, the foreign matter 12 can enter the slit-shaped opening 6 between the metal thin plates 5 in the first filter plate 4 on the upstream side. You can only move in and stay there, you cannot go downstream.

Here, assuming that the cross-sectional area of the flow path of the lower tie plate 1 at the mounting position of the foreign matter capturing filter member 3 is S1 and the opening area of the small holes 8 is S2, the first filter plate 4 is located upstream. Does not exist, the foreign matter can freely move around the surface of the second filter plate 7, so that the foreign matter is sucked into the pores 8 and enters the fuel rod region F1.
Can be expressed as F1 = n ² × S2 / S1.

On the other hand, when the first filter plate 4 having the slit-shaped openings 6 is provided on the upstream side of the second filter plate 7 as in the present invention, the foreign matter that has entered the slit-shaped openings 6 is reduced. , Can move only within the range of the slit-shaped apertures 6. Assuming that the probability of the foreign matter being sucked into the pores 8 at that time is F2, F2 = n × S2
/ S1.

Accordingly, the ratio of the probability of foreign matter being sucked into the pores 8 when the first filter plate 4 is present on the upstream side and when the first filter plate 4 is not present is F2 / F1 = 1 / n. Is provided on the upstream side, the ratio of foreign matter entering the fuel rod region is greatly reduced to 1 / n.

If the coolant flow path composed of the slit-shaped openings 6 is separated by y other thin metal plates extending in a direction perpendicular to the longitudinal direction of the slit-shaped openings 6, foreign matter may be present. The rate of intrusion into the fuel rod side can be further reduced to 1 / (y + 1) n.

As described above, by arranging such a slit filter on the upstream side, the movement of the foreign matter 12 is greatly restricted and the foreign matter is trapped as compared with the case where only a single multi-pore filter plate is arranged. It works better as a filter member.

Next, as shown in FIG. 4, the flow path width of the slit-shaped opening 6 of the first filter plate 4 is narrower, and the gap width between the first filter plate 4 and the second filter plate 7 is further reduced. If the foreign substance 13 is thinner than X, the foreign substance 13
After flowing into the slit-shaped opening 6, it may enter the gap between the first filter plate 4 and the second filter plate 7.

However, the foreign matter 13 is sucked into the pores 8 of the second filter plate 7 on the downstream side when the axis of the foreign matter 13 is parallel to the central axis of the pores 8. However, at this time, the first filter plate 7
Is present, even if the foreign matter 13 tries to make its axis parallel to the axis of the pore 8 by the flow of the coolant,
The other end of the foreign matter 13 is suppressed by the thin metal plate 5 of the first filter plate 4, so that it is difficult for the foreign matter 13 to be sucked into the fine holes 8.

As described above, according to the filter member 3 for capturing foreign matter according to the present embodiment, the filter plate having the slit-shaped openings formed upstream of the filter plate having the large number of pores 8 is provided with the predetermined gap. With such a configuration, foreign substances can be efficiently captured in a stepwise manner, and the pressure loss can be satisfactorily captured while maintaining the pressure loss within a required range.

The pressure loss of the fuel assembly irradiated in the reactor is required to be within a predetermined range. However, the fuel loss of the fuel assembly currently used in the boiling water reactor is required. While the rod arrangement is 8 rows and 8 columns and 9 rows and 9 columns, a multi-row and multi-column fuel assembly aiming at higher burnup is being developed in the future.

If the fuel rod arrangement changes, the pressure loss in the fuel rod region in the fuel assembly also changes, so that it is necessary to change the pressure loss in the lower tie plate. Here, if the foreign matter trapping mechanism includes the lower tie plate fuel rod support part and is provided so as to be flush with or contact with the fuel rod support part, the structure or size of the foreign matter trap part each time the fuel rod arrangement changes. However, providing such a mechanism between the fuel rod supports is limited in size and strength, and it is very important to develop a foreign material trap for a new fuel rod arrangement. It takes a lot of time and money.

However, the foreign matter trapping filter member 3 of the present embodiment has a simple structure in which the first filter plate 4 is arranged on the upstream side and the second filter plate 7 is arranged on the downstream side, and the lower type is used. Since it is built in a position that is not affected by the fuel rod support of the rate 1 (upper support plate 2), even if the fuel rod arrangement is changed, the size and number of holes and the distance between both plates (4, 7) It is possible to easily adjust the pressure loss to a predetermined value only by increasing or decreasing the pressure. This greatly contributes to the increase in the degree of freedom in designing the fuel assembly to increase the burnup and the cost reduction for developing a new foreign matter capturing mechanism.

As a method for incorporating the foreign matter capturing filter member of the present invention in the lower tie plate, a method with as few steps and parts as possible is desired. For example, one of the simplest procedures is one that can utilize a lower tie plate formed by a conventional manufacturing method as shown in FIG.

That is, in the same manner as in the prior art, the lower tie plate 1 formed by integrally casting the fuel rod support upper plate 2 and the filter member 3 for capturing foreign matter are provided at a predetermined height position on a pair of inner wall surfaces facing each other. An opening window 9 that can be inserted is formed. This can be easily formed by machining or wire electric discharge machining.

After the foreign matter trapping filter member 3, which has been constructed by combining the first filter plate 4 and the second filter plate 7, is inserted into the lower tie plate 1 from the opening window 9, the window is opened. In the portion, the filter member 3 and the window rim of the lower tie plate 1 are welded. Thereafter, the outer surface of the lower tie plate is processed as before. According to this method, it is possible to supply the lower tie plate incorporating the foreign matter capturing filter member at a relatively low cost without much difference from the conventional process.

In addition to the method using such an opening window, for example, as shown in FIG. 6A, the lower tie plate 1 is vertically moved between the fuel rod supporting upper plate 2 side and the nosepiece side. A simple method is to divide the filter member 3 between them. In this case, the lower tie plate 1 manufactured and manufactured in the same manner as the conventional one is completely cut and divided into upper and lower parts, or is separately manufactured and manufactured from the beginning to obtain two upper and lower members (1x, 1y). As shown in FIG. 6B, the upper member 1x,
The filter member 3 and the lower member 1y are laminated in three layers, and the surfaces of adjacent members are fixed by welding, or the filter member 3 is attached to a fitting portion provided between the upper and lower members as shown in FIG.
The upper and lower members may be welded and fixed after being fitted and stored.

As described above, it is necessary to determine the design of the filter member for trapping foreign matter so that a predetermined coolant flow pressure loss according to the design of the fuel rod assembly is obtained. Pressure loss can be easily adjusted by adjusting the size and number.

For example, as shown in the schematic plan views of FIGS. 7A and 7B, the pores of the second filter plate have the same diameter as the pores (28, 38). The pressure loss can be changed by changing the number in (27, 37). Here, as compared with the high-pressure loss type of the filter plate 27 shown in FIG.
The low pressure loss type filter plate 37 is obtained.

The shape of the pores of the second filter plate is circular, which is simple in design and manufacture. However, the present invention is not limited to this. The elliptical pores 48 as shown in FIG.
Any of a rectangular pore 58 as shown in FIG. 8B, a rectangular pore 68 as shown in FIG. 8C, and a polygonal pore 78 as shown in FIG.

As shown in FIG. 9, the second filter plate 87 on the downstream side is also provided with a plurality of thin metal plates 85 similar to the first filter plate 84 on the upstream side.
A plate may be used where 6 is formed. In this case, when the two metal thin plates 85 are combined so as to be substantially perpendicular to each other, an apparent lattice-shaped channel 88 is formed. As described above, even in this case, excellent foreign matter capturing performance can be expected.

In the present invention, it is recommended to use a perforated plate for the second filter plate on the downstream side in consideration of the strength of the plate. The use of a slit plate does not pose a problem in the foreign matter capturing performance.

[0052]

As described above, according to the lower tie plate of the present invention, in the fuel assembly used in the nuclear reactor, the foreign matter trapped in the coolant by the foreign matter trapping filter member built in the lower tie plate. Is well captured without causing an increase in pressure loss, and it is very difficult for foreign matter to enter the fuel rod region of the fuel assembly. Therefore, there is an effect that damage to the fuel rod due to fretting or the like can be prevented.

Further, even when the fuel rod arrangement of the fuel body is changed, the structure of the fuel rod supporting portion can be easily adjusted to have a predetermined pressure loss without affecting each other. Adjustment changes can be made.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a lower plate of a fuel assembly for a boiling water reactor according to an embodiment of the present invention, and (a).
FIG. 2 is a schematic configuration diagram of a lower tie plate, and FIG. 2B is a plan view of a foreign matter capturing filter member in the lower tie plate as viewed from an upstream side of a coolant flow.

FIGS. 2A and 2B are schematic diagrams illustrating a foreign matter capturing state by the foreign matter capturing filter member of the present invention, wherein FIG. 2A is a plan view of the filter member, and FIG.

FIGS. 3A and 3B are schematic diagrams illustrating a foreign matter capturing state by the foreign matter capturing filter member of the present invention, wherein FIG. 3A is a plan view of the filter member, and FIG.

FIGS. 4A and 4B are schematic views illustrating a foreign matter capturing state by the foreign matter capturing filter member of the present invention, wherein FIG. 4A is a plan view of the filter member, and FIG.

FIG. 5 is a schematic process chart showing an example of a method for manufacturing the lower tie plate of FIG. 1;

FIG. 6 is a schematic process chart showing another example of a method for manufacturing a lower tie plate.

FIG. 7 is a schematic plan view showing another pore design of the second filter plate of the present invention.

FIG. 8 is a schematic plan view showing another pore design of the second filter plate of the present invention.

FIG. 9 is a schematic configuration diagram showing another configuration example of the foreign matter capturing filter member of the present invention, where (a) is a schematic plan view and (b).
Is an immediate sectional view.

[Explanation of symbols]

 1: Lower tie plate of a fuel assembly for a boiling water reactor 1x: Upper member of a lower tie plate 1y: Lower member of a lower tie plate 2: Upper support plate 3: Filter member for trapping foreign matter 4, 84: First filter plate 5,85; metal thin plate 6,86: slit-shaped opening 7, 27, 37, 87: second filter plate 8, 28, 38, 48, 58, 68, 78: pore 9: opening window X: Gap width between first and second filter plates 11, 12, 13: Foreign matter 88: Lattice flow path

Claims (4)

[Claims] 1. A lower tie plate of a fuel assembly for a boiling water reactor, wherein a number of fuel rods are supported at upper and lower ends by an upper tie plate and a lower tie plate as a bundle in a predetermined square lattice arrangement, A flat plate-like foreign matter trapping filter member is built in a position below the upper support plate that supports the lower end plug of the fuel rod and is not in contact with the upper support plate, and the foreign matter trapping filter member is provided with a coolant flow in a lower tie plate. A plurality of rows of slit-shaped apertures are formed by horizontally arranging a number of thin metal plates having a predetermined width and thickness on a substantially square frame member in parallel at predetermined intervals. A first filter plate,
A second filter plate, which is arranged downstream from the first filter plate and has a large number of pores formed in a metal plate, is combined in a face-to-face state at a predetermined interval in parallel with each other. The lower tie plate of the boiling water reactor fuel assembly. 2. The boiling water type atom according to claim 1, wherein a built-in position of the foreign matter trapping filter member is a position where a cross-sectional area of a coolant flow path in the lower tie plate is maximum. Lower tie plate of reactor fuel assembly. 3. A lower tie plate of a boiling water reactor fuel assembly wherein a number of fuel rods are supported at upper and lower ends by an upper tie plate and a lower tie plate as a bundle in a predetermined square lattice arrangement, A flat plate-like foreign matter trapping filter member is built in a position below the upper support plate that supports the lower end plug of the fuel rod and is not in contact with the upper support plate, and the foreign matter trapping filter member is provided with a coolant flow in a lower tie plate. A plurality of rows of slit-shaped apertures are formed by horizontally arranging a number of thin metal plates having a predetermined width and thickness on a substantially square frame member in parallel at predetermined intervals. A first filter plate,
A second filter plate disposed downstream from the first filter plate and provided with a large number of pores in a metal plate, and combined in a face-to-face state in which they are in close contact with each other; Lower tie plate of a reactor fuel assembly. 4. The boiling water atom according to claim 3, wherein the built-in position of the foreign matter trapping filter member is a position where a cross-sectional area of a coolant flow path in the lower tie plate is maximum. Lower tie plate of reactor fuel assembly.