JP2005172741A - Lower tie-plate and fuel assembly equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lower tie-plate capable of reducing the effect of flow channel blockage due to deposition of water scale and efficiently capturing linear shape foreign articles, and fuel assembly equipped with this. <P>SOLUTION: The lower tie-plate 6 of a reactor fuel assembly 1 comprises a first filter layer 16 provided with a multitude of flow channels 21 formed long and with bend in the direction nearly perpendicular to the coolant flow direction, and a second filter layer 17 downstream side of the first filter layer 16 which is provided with a multitude of flow channels 23 formed long and with bend in the direction nearly perpendicular to the coolant flow direction opposite to the bend direction of the flow channels 21 of the first filter layer 16. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel assembly used in a nuclear reactor core and a lower tie plate for supporting the fuel assembly, and in particular, includes means for preventing foreign matter from entering the fuel assembly. The present invention relates to a lower tie plate and a fuel assembly including the same.

  In general, a fuel assembly used in a core of a boiling water reactor or the like includes a plurality of fuel rods that are filled with a large number of nuclear fuel pellets and sealed therein, and light water (in which a neutron moderator and a coolant are also contained) Hereinafter, one or a plurality of water rods having a structure in which a coolant flows, a plurality of spacers that are bundled at a predetermined interval so that the fuel rods and the water rods are arranged in a square lattice pattern, and the fuel rods and the water rods The upper and lower tie plates that respectively support the upper and lower ends and a rectangular tube-shaped channel box that covers the outer sides of the upper and lower tie plates are provided. With respect to the fuel assembly configured as described above, the coolant flows from an opening provided at the lower end of the lower tie plate and is introduced into the fuel assembly via the fuel rod support portion of the lower tie plate. , Flows around the fuel rod and inside the water rod. At this time, steam is generated, and the mixture of water and steam flows out above the fuel assembly via the upper tie plate.

  Here, if a foreign object such as a metal piece or wire of construction material is accidentally mixed into the coolant circulation system during construction or repair of the nuclear power plant, the flow of circulating coolant It is conceivable to move by riding. At this time, if the foreign matter is large enough to not pass through the lower tie plate of the fuel assembly, it is blocked by the lower tie plate and does not flow into the fuel assembly, but the foreign matter passes through the lower tie plate. If possible, it may flow into the fuel assembly. In that case, if the foreign matter is sufficiently small, it will flow out of the upper tie plate with the flow of the coolant without staying in the fuel assembly, but if it is of an appropriate size, for example, the fuel rod and the spacer There is a possibility of entering and fixing the gap. In such a case, the foreign matter may vibrate due to the flow of the coolant in contact with the fuel rods, causing abnormal wear (so-called fretting wear) to the fuel rods and possibly causing damage.

  In order to prevent such damage to the fuel assembly due to the inflow of such foreign matter, conventionally, a space between the inlet opening portion of the lower tie plate and the upper end portion supporting the fuel rod or the like or the coolant flow path in the upper end portion Some have a capturing means for capturing foreign matter in a grid-like flow path formed by a boss that supports a fuel rod or a water rod and a web that connects the bosses. As a conventional technique of the lower tie plate having such a capturing means, a dome-shaped capturing means (debris capturing lattice structure) having a large number of openings between an inlet opening and an upper end (for example, a debris capturing lattice structure) , Patent Document 1), a device provided with a pyramidal trapping means having a large number of openings in the coolant channel at the upper end (see, for example, Patent Document 2), cooling between the inlet opening and the upper end A first capture means in which a plurality of rectangular slit-shaped flow paths are formed from the upstream side in the water flow direction and a second capture means having a large number of openings (see, for example, Patent Document 3), inlet opening The first capturing means in which a plurality of rectangular slit-shaped flow paths are formed between the upper end portion and the upper end portion are provided so that the length direction of the slit-shaped flow paths is orthogonal to the flow path of the first capturing means. Provided with second capturing means (for example, see Patent Document 4) A.

JP-A-7-306280

JP-A-8-240678 JP 2002-62392 A JP 2001-337187 A

However, there are the following problems in the above-described prior art.
That is, according to the prior art described in Patent Document 1 and Patent Document 2, the surface area of the capturing means is increased and the number of openings is increased by making the capturing means have a three-dimensional structure such as a dome shape or a pyramid shape. As a result, it is possible to improve the foreign matter separation performance by reducing the opening area while avoiding the increase in pressure loss, but clogging due to the adhesion of the clad (scale) and the trapping of foreign matter due to the small opening. Concerned. In addition, it is considered that the foreign matter that enters the gap between the fuel rod and the spacer as described above and causes the fretting wear of the fuel rod is a linear foreign matter such as a thin wire. In the case of such a linear foreign matter, In the capturing means having the structure as in Patent Document 1 and Patent Document 2, the capturing surface is inclined with respect to the flow direction of the coolant because the capturing means has a dome shape or a pyramid shape even if it can be captured once. Therefore, while moving on the surface, the posture of the linear foreign substance fluctuates so that its length direction becomes substantially parallel to the flow direction of the coolant, and is sucked into the opening and passes through the capturing means. There is a risk of doing.

  In order to prevent such passage of the linear foreign matter, it is effective to make the capturing surface of the capturing means substantially perpendicular to the flow direction of the coolant and to reduce the movement on the captured surface. Therefore, according to the prior art described in Patent Document 3, the first capturing means in which a plurality of rectangular slit-shaped flow paths are formed and the second capturing means having a large number of openings are used in the flow direction of the coolant. Are stacked so as to be substantially perpendicular to the first trapping means, so that the movement of the linear foreign matter captured by the second capturing means can be limited to the space in the slit-like flow path of the first capturing means. The possibility that a foreign substance passes through the second capturing means can be reduced. However, with regard to clogging due to the adhesion of the clad (scale) and the trapping of foreign matter, the flow path is obstructed without clogging the single flow path because the flow path of the first capturing means is a rectangular slit. However, there is a risk of clogging because the second capturing means in the subsequent stage has a large number of openings.

  In order to prevent such clogging due to the adhesion of the clad (scale) and the trapping of foreign substances, it is effective to configure the trapping means only with a slit-like channel. Therefore, according to the prior art described in the above-mentioned Patent Document 4, the first and second capturing means both have a structure in which a plurality of rectangular slit-shaped channels are formed, so that the single channel is clogged. Therefore, the influence of the channel blockage can be reduced. However, in the case of a linear foreign object, if the length is equal to or less than the length in the longitudinal direction of the flow path, even if it is once captured by the first capturing means, There is a high possibility that the length direction and the longitudinal direction of the flow path substantially coincide and pass through the first capturing means. That is, in the case of a linear foreign object, in many cases, it is captured by the second capturing means, so that the flow is greater than when the first capturing means and the second capturing means capture foreign matter in a balanced manner. It is not sufficient in terms of reducing the influence of road blockage, and there is room for further improvement.

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to efficiently capture linear foreign matters while reducing the influence of channel blockage due to adhesion of foreign matter or foreign matter. An object of the present invention is to provide a lower tie plate and a fuel assembly including the same.

  (1) In order to achieve the above object, the present invention provides a large number of elongated and bent in a direction substantially perpendicular to the coolant flow direction in the lower tie plate of a nuclear fuel assembly. It shall have a flow path and have a capturing means for capturing foreign matter in the coolant.

  In general, in a boiling water reactor, a coolant flows from an opening provided at the lower end of a lower tie plate, passes through a trapping means of the lower tie plate, removes foreign matter, and then enters the fuel assembly. It flows in around the fuel rod and inside the water rod. At this time, steam is generated, and a mixture of water and steam flows out above the fuel assembly via the upper tie plate.

  Here, when the capturing means is a dome-shaped or pyramid-shaped structure having a large number of openings as in the above-described prior art (Patent Document 1 and Patent Document 2), the capturing means can be obtained by adopting such a three-dimensional shape. The surface area can be increased to increase the number of openings, and as a result, the opening area can be reduced and the foreign matter separation performance can be improved while avoiding an increase in pressure loss. There is a concern about clogging due to adhesion of foreign substances and trapping of foreign substances. In addition, when linear foreign substances such as thin wires that are considered to be the cause of fretting wear of the fuel rods are mixed in the coolant, the trapping means is dome-shaped or pyramid-shaped even if it can be trapped once by the trapping means. Since the trapping surface is inclined with respect to the flow direction of the coolant, the length of the linear foreign object is approximately parallel to the flow direction of the coolant while moving on the surface. There is a risk that the air will be sucked into the opening and passed through the capturing means.

  In order to prevent such passage of the linear foreign matter, it is effective to make the capturing surface of the capturing means substantially perpendicular to the flow direction of the coolant and to reduce the movement on the captured surface. Therefore, according to the above-described prior art (Patent Document 3), the first capturing means in which a plurality of rectangular slit-shaped flow paths are formed and the second capturing means having a large number of openings are used as the coolant. Therefore, the movement of the linear foreign matter captured by the second capturing means is limited to the space in the slit-like flow path of the first capturing means. It is possible to reduce the possibility that the linear foreign matter passes through the second capturing means. However, with regard to clogging due to the adhesion of the clad (scale) and the trapping of foreign matter, the flow path is obstructed without clogging the single flow path because the flow path of the first capturing means is a rectangular slit. Although the structure is small, there is a risk of clogging because the second capturing means at the subsequent stage is a structure having a large number of openings.

  In order to prevent such clogging due to the adhesion of the clad (scale) and the trapping of foreign substances, it is effective to configure the trapping means only with a slit-like channel. Therefore, according to the above-described prior art (Patent Document 4), since the first and second capturing means have a structure in which a plurality of rectangular slit-shaped channels are formed, the single channel is clogged. Therefore, the influence of the channel blockage can be reduced. However, in the case of a linear foreign object, if the length is equal to or less than the length in the longitudinal direction of the flow path, the length of the linear foreign object is still moving while moving on the surface once captured by the first capturing means. There is a high possibility that the longitudinal direction of the flow path and the longitudinal direction of the flow path substantially coincide and pass through the first capturing means. That is, in the case of a linear foreign object, in many cases, it is captured by the second capturing means, so that the flow is greater than when the first capturing means and the second capturing means capture foreign matter in a balanced manner. It is not sufficient in terms of reducing the influence of road blockage, and there is room for further improvement.

  On the other hand, in the present invention, the trapping means is composed of a large number of channels that are elongated and bent in a direction substantially perpendicular to the flow direction of the coolant, for example, and traps foreign matter in the coolant. The first capturing means and a large number of flow paths that are elongated and bent in a direction substantially perpendicular to the flow direction of the coolant, and the bending direction is the bending of the flow path of the first capturing means. The second capturing means is provided downstream of the first capturing means so as to be opposite to the direction. In this way, by making the flow paths of the first capturing means and the second capturing means both elongated slits in a direction substantially perpendicular to the flow direction of the coolant, adhesion of clad (scale) and foreign matter The single flow path is not clogged by the capture, and clogging can be suppressed. Further, in the case of a linear foreign object, since the flow path is bent, a linear foreign object having a predetermined length or more cannot pass through the first capturing means. It can be captured by the first capturing means. On the other hand, linear foreign matters having a predetermined length or less that have passed through the first capturing means are captured by the second capturing means provided so that the bending direction of the flow path is opposite to that of the first capturing means. The As a result, the linear foreign matter is caught by the first catching means for the linear foreign matter having a relatively long length, and the second catching means for the linear foreign matter having a relatively short length. As a result, it is possible to efficiently capture in a stepwise manner according to the length, and as a result, the trapping positions of the linear foreign matter are dispersed without being partially biased as in the prior art described in Patent Document 4 described above. The influence of occlusion can be reduced. Furthermore, according to the present invention, the flow channel area (opening area) of a single flow channel can be increased by bending the flow channel as compared with a rectangular flow channel, thereby reducing the influence of the flow channel blockage. Can do.

  As described above, according to the present invention, it is possible to efficiently capture linear foreign matters while reducing the influence of flow path blockage due to adhesion of scales or trapping of foreign matters.

  (2) In order to achieve the above object, the present invention is a large number of slender and bent in a direction substantially perpendicular to the coolant flow direction in the lower tie plate of the nuclear fuel assembly. And a first capturing means having the first flow path, and elongated in a direction substantially perpendicular to the flow direction of the coolant and bent in a direction opposite to the bending direction of the first flow path. And a plurality of second flow paths, and second capture means provided on the downstream side of the first capture means.

  (3) In the above (1) or (2), preferably, the flow path or the bent portion of the first and second flow paths has an angular shape.

  (4) In the above (1) or (2), preferably, the flow path or the bent portion of the first and second flow paths has a round shape.

  (5) In any one of the above (1) to (4), and preferably, the capturing means or the first and second capturing means are provided on a plurality of bent thin plates and the thin plates, respectively. It has a plurality of spacers for laminating thin plates at regular intervals.

  (6) In any one of the above (1) to (5), and preferably, a flow guiding means for guiding the flow direction of the coolant in a direction substantially perpendicular to the flow direction is the capturing means or the first. It is provided in close contact with the upstream side of the capturing means.

  In the present invention, the flow direction of the coolant is guided in a direction substantially perpendicular to the flow direction by the flow guide means, and the capture means (or the first capture means) provided in close contact with the downstream side thereof. To introduce. As a result, the posture of the linear foreign matter mixed in the coolant is changed so that the length direction is substantially perpendicular to the flow direction of the original coolant, and then the capture means (or the first capture) Means). Therefore, for example, even when the linear foreign matter flows in such a posture that the length direction thereof is substantially parallel to the flow direction of the coolant, the foreign matter separation performance can be improved.

  (7) In the above (6), more preferably, the flow guiding means includes a plurality of projecting portions provided so as to project toward the upstream side of the capturing means or the first capturing means, and the plurality of projecting portions. It shall have the coolant inlet hole each provided in the side surface of the protrusion part.

  (8) In order to achieve the above object, a fuel assembly of the present invention includes the lower tie plate according to any one of (1) to (7).

  According to the present invention, the flow path of the first capturing means and the second capturing means is formed into an elongated slit shape in a direction substantially perpendicular to the flow direction of the coolant, so that the adhesion of the clad and the capturing of the foreign matter are performed. Therefore, the single flow path is not clogged, and clogging can be suppressed. Furthermore, by making these flow paths bent in a direction substantially perpendicular to the flow direction of the coolant, linear foreign matters having a relatively long length are captured by the first capturing means, and compared. The linear foreign matter can be efficiently captured step by step according to the length of the linear foreign matter having a short target length as captured by the second capturing means. Since the capturing positions are dispersed without being partially biased, the influence of the channel blockage can be reduced. Furthermore, since the channel area (opening area) of the single channel can be increased by bending the channel, the influence of the channel blockage can also be reduced. Therefore, it is possible to efficiently capture linear foreign matters while reducing the influence of flow path blockage due to adhesion of scales or foreign matter capture.

  Hereinafter, an embodiment of a lower tie plate of the present invention and a fuel assembly including the same will be described with reference to FIGS. 1 to 10.

FIG. 1 is a side sectional view showing the overall structure of a fuel assembly including an embodiment of a lower tie plate of the present invention.
In FIG. 1, a fuel assembly 1 includes a plurality of fuel rods 2 in which a large number of nuclear fuel pellets (not shown) are loaded and sealed, and one or a plurality of hollow structure waters through which coolant flows. The rod 3, the fuel rods 2 and the water rods 3 support a plurality of spacers 4 that are bundled at a predetermined horizontal interval so as to form a square lattice arrangement, and the upper and lower ends of the fuel rods 2 and the water rods 3 are supported respectively. The upper and lower tie plates 5 and 6 and the rectangular tube-shaped channel box 7 covering the outer sides thereof are provided.

FIG. 2 is a side sectional view schematically showing the internal structure of the lower tie plate 6.
In FIG. 2, the lower tie plate 6 is provided with a housing 10, an opening 11 provided at the lower end of the housing 10, and an upper end of the housing 10, and supports the lower ends of the fuel rod 2 and the water rod 3. A plurality of bosses 12 and a web 13 interconnecting the bosses 12 form a plurality of flow openings (not shown) to allow coolant to pass in a predetermined flow direction, and the housing 10. A first filter layer (capturing means; first capturing means) 16 and a second filter layer that are provided in a hollow region 15 formed between the opening 11 in the inner wall and the lattice 14 and capture foreign matter in the coolant. (Capturing means; second capturing means) 17. The first and second filter layers 16 and 17 are laminated in the order of the first filter layer 16 and the second filter layer 17 from the upstream side in the coolant flow direction (the lower side in FIG. 2). It is arrange | positioned so that it may become substantially right angle with respect to the flow of this. With such a configuration, the coolant flowing into the lower tie plate 6 from the lower side of the fuel assembly 1 through the opening 11 passes through the first and second filter layers 16 and 17 to remove foreign matter, and the lattice is removed. The upper fuel rod 2 and the water rod 3 are guided through the space 14.

FIG. 3 is a plan view showing the entire structure of the first filter layer 16, and FIG. 4 is a plan view showing the entire structure of the second filter layer 17.
As shown in FIGS. 3 and 4, the first filter layer 16 is an elongated shape that is bent into a substantially square shape (or a substantially square shape, that is, a shape in which a bent portion is angular) on a substantially square plate 20. A large number of slit-shaped flow paths (first flow paths) 21 are formed in the thickness direction of the plate 20 (direction perpendicular to the paper surface in FIG. 3). The flow path 21 is bent and arranged in the same direction along the left-right direction in FIG. 3 of the board 20, and they form one flow path group 21A. The first filter layer 16 is provided with a plurality of rows (21 rows 8A, 21A1 to 21A8 in this embodiment) of the flow passage groups 21A in the vertical direction in FIG. 3 of the plate 20, and the flow passage groups 21A1 to 21A8. In adjacent channel groups, the bending directions of the slits 21 are opposite to each other.

  On the other hand, the second filter layer 17 has a structure similar to that of the first filter layer 16 and has a substantially square shape (or a substantially square shape, that is, a shape in which the bent portion is angular) on the substantially square plate 22. A number of bent slit-like flow paths (second flow paths) 23 are formed in the thickness direction of the plate 22 (direction perpendicular to the paper surface in FIG. 4) and bent in the same direction along the left-right direction in FIG. As a result, they form one flow path group 23A, but the bending direction of the slit 23 of the second filter layer 17 is opposite to the bending direction of the corresponding slit 21 of the first filter layer 16. It has become. That is, the flow path group 23A1 of the second filter layer 17 is bent so as to protrude rightward in FIG. 4, but corresponds to the flow path group 23A1 (that is, disposed upstream of the flow path group 23A1). The flow path group 21A1 of the first filter layer 16 is bent so as to protrude leftward in FIG. The other channel groups 23A2 to 23A8 and the channel groups 21A2 to 21A8 have the same relationship.

  In this way, by arranging the first filter layer 16 and the second filter layer 17 so that the bending directions of the corresponding flow path groups 21A and 23A (slits 21 and 23) are opposite to each other. As shown in FIG. 5, the flow channel regions 24 (shaded regions in FIG. 5) penetrating the filter layers 16 and 17 are arranged in a lattice pattern. Thereby, the foreign substance separation performance can be remarkably improved.

Next, the operation of the embodiment of the lower tie plate of the present invention and the fuel assembly including the same will be described below.
The coolant that has flowed into the lower tie plate 6 from below the fuel assembly 1 through the opening 11 passes through the first and second filter layers 16 and 17 to remove foreign matters, and passes upward through the lattice 14. The fuel rod 2 and the water rod 3 are introduced into the fuel assembly 1 in which they are housed. Then, steam is generated, and a mixture of water and steam flows out above the fuel assembly 1 via the upper tie plate 5.

  Here, there are many capturing means (in this embodiment, the first and second filter layers 16 and 17) for removing foreign substances from the coolant as in the above-described prior art (Patent Document 1 and Patent Document 2). In the case of a dome-shaped or pyramidal structure having openings, such a three-dimensional shape increases the surface area of the capturing means to increase the number of openings, and as a result, avoids an increase in pressure loss. Although it is possible to improve the foreign matter separation performance by reducing the area, there is a concern about clogging of the opening due to adhesion of clad (scale) or trapping of foreign matter by making the opening small. In addition, when linear foreign substances such as thin wires that are considered to be the cause of fretting wear of the fuel rods are mixed in the coolant, the trapping means is dome-shaped or pyramid-shaped even if it can be trapped once by the trapping means. Therefore, the trapping surface is inclined with respect to the coolant flow direction (inclined so as to be smaller than the right angle with respect to the coolant flow direction). May change so that its length direction is substantially parallel to the flow direction of the coolant and be sucked into the opening and pass through the capturing means.

  In order to prevent such passage of the linear foreign matter, it is effective to make the capturing surface of the capturing means substantially perpendicular to the flow direction of the coolant and to reduce the movement on the captured surface. Therefore, as in the prior art (Patent Document 3) described above, the first capturing means in which a plurality of rectangular slit-shaped flow paths are formed and the second capturing means having a large number of openings are used as the coolant. If the structure is laminated so as to be substantially perpendicular to the flow direction, the movement of the linear foreign matter captured by the second capturing means can be limited to the space in the slit-like flow path of the first capturing means. The possibility that the linear foreign matter passes through the second capturing means can be reduced. However, with regard to clogging of the opening due to adhesion of the clad (scale) and trapping of foreign substances, the flow path of the first capturing means is a rectangular slit, so the single flow path is not clogged and the flow path is blocked. However, since the second capturing means on the downstream side has a structure having a large number of openings, there is a risk of clogging.

  In order to prevent such clogging due to the adhesion of the clad (scale) and the trapping of foreign substances, it is effective to configure the trapping means only with a long and narrow slit-like flow path. Therefore, as in the above-described prior art (Patent Document 4), since the first and second capturing means have a structure in which a plurality of rectangular slit-shaped channels are formed, the single channel is clogged. Therefore, the influence of the channel blockage can be reduced. However, in the case of a linear foreign object, if the length is equal to or less than the length in the longitudinal direction of the flow path, the length of the linear foreign object is still moving while moving on the surface once captured by the first capturing means. There is a high possibility that the longitudinal direction of the flow path and the longitudinal direction of the flow path substantially coincide and pass through the first capturing means. That is, in the case of a linear foreign matter, in many cases it will be caught by the second catching means, so compared with the case where the linear foreign matter is caught in a balanced manner by the first catching means and the second catching means. This is not sufficient from the viewpoint of reducing the influence of the channel blockage, and there is room for further improvement.

  On the other hand, in the present embodiment, the first filter layer 16 having a large number of flow paths formed by elongating and bending the capturing means in a direction substantially perpendicular to the flow direction of the coolant, Provided on the downstream side of the first filter layer 16 and formed to be elongated in a direction substantially perpendicular to the flow direction of the coolant and bent in a direction opposite to the bending direction of the flow path 21 of the first filter layer 16. The second filter layer 17 includes a large number of flow paths 23. In this way, by forming both the flow path 21 of the first filter layer 16 and the flow path 23 of the second filter layer 17 into an elongated slit shape in a direction substantially perpendicular to the flow of the coolant, a large number of openings are formed in a lattice shape. It is possible to suppress clogging of a single flow path that may occur due to adhesion of clad (scale) or trapping of foreign matter like the trapping means having. Furthermore, according to the present embodiment, it is possible to efficiently capture linear foreign matters. This will be described below with reference to FIG. FIG. 6 shows a linear foreign matter by the first and second filter layers 16 and 17 (channel 21) of the present embodiment and a trapping means (rectangular slit-shaped channel) as in the above-described prior art (Patent Document 4). It is the conceptual diagram which compared the capture state of.

The 6, according to a rectangular slit-shaped flow path of the conventional structure, both a relatively long linear foreign matters D _L and a relatively short linear foreign matters D _S is captured by entering the slits Since the trapped linear foreign matter is biased to a partial area in the slit, the influence of the blockage of the flow path is increased.

In contrast, according to the first and second filter layers 16 and 17 of the present embodiment, in the case of relatively long (in FIG. 6 longer than the length L) linear foreign matters D _L has a passage 21 Since it cannot be passed through the first filter layer 16 because it is bent, it can be captured by the first filter layer 16. On the other hand, in the case of relatively short (figure 6 below the length L) linear foreign matters D _S is capable entering into the flow path 21 of the first filter layer 16, in which case the second filter layer 17 Will be captured (see also FIG. 5). Note that the length L of the linear foreign matter that can be captured by the first filter layer 16 can be adjusted by the dimensions (width W, length L ₂ ) of the flow path 21. Thus, according to this embodiment, relatively to the length of a long linear foreign matters D _L is caught by the first filter layer 16, for a relatively short length linear foreign matters D _S is the second filter As in the case of capturing by the layer 17, the linear foreign matter can be efficiently captured stepwise according to the length. As a result, the trapping position of the linear foreign matter is dispersed without being biased to a part of the area as in the conventional structure, so that the influence of the channel blockage can be reduced.

Furthermore, according to the present embodiment, since the flow path 21 (flow path 23) is bent, a single flow path area (opening area) can be increased as compared with a rectangular flow path having a conventional structure. (That is, as shown in FIG. 6, when the width of both channels is W, the channel area of the channel 21 of this embodiment is about ₂ WL ₂ , whereas the flow rate of the conventional structure is The road area is WL ₁ and 2WL ₂ > WL ₁ ). Also by this, the effect of reducing the influence of the channel blockage can be obtained.

  From the above, according to the present embodiment, it is possible to efficiently capture linear foreign matters while reducing the influence of channel blockage due to the adhesion of scales and the capturing of foreign matters. As a result, it is possible to improve the reliability of the fuel assembly and to contribute to the improvement of the operating rate of the nuclear power plant.

  As the lower tie plate capturing means of the present invention, various modifications other than the first and second filter layers 16 and 17 are conceivable. FIG. 7 is a plan view illustrating a modification in which the flow path shape of the filter layer is partially enlarged.

  As shown in FIG. 7, in the above-described embodiment, the shapes of the flow paths 21 and 23 of the first and second filter layers 16 and 17 are substantially U-shaped (or substantially U-shaped. The channel shape may be a substantially C-shape (or a substantially U-shape, that is, a shape having a rounded bent portion). Even if the first and second filter layers 16 ′ and 17 ′ having such flow paths 21 ′ and 23 ′ are used, the same effect as that of the above-described embodiment can be obtained.

  In the above embodiment, the first and second filter layers 16 and 17 have a structure in which the flow paths 21 and 23 are formed in the plates 20 and 22. However, the present invention is not limited to this. You may make it comprise with a thin plate. FIG. 8 is a partially enlarged perspective view showing the structure of the filter layer of the present modification. FIG. 9 is a plan view of the structure of the filter layer of the present modification partially seen from the coolant flow direction. FIG.

  As shown in FIGS. 8 and 9, the first and second filter layers 16 ″ and 17 ″ of this modification are composed of a large number of thin plates (bent thin plates) 27 processed into wave shapes. A large number of thin plates 27 are stacked at a predetermined interval by a plurality of spacers 28, whereby a flow path 29 is formed between adjacent thin plates 27 and 27. As in the above-described embodiment, the first filter layer 16 ″ and the second filter layer 17 ″ formed of the thin plate 27 are arranged so that the corresponding flow direction of the flow path 29 is opposite to the first filter layer 16 ″ and the second filter layer 17 ″. Each flow path 29 is disposed so as to be elongated and bent in a direction substantially perpendicular to the flow direction of the coolant. Also by this modified example having the above-described configuration, the same effect as that of the above-described one embodiment can be obtained.

  In addition, a flow guiding means is provided on the upstream side of the first and second filter layers 16 and 17 in the above embodiment, and the posture of the linear foreign matter in the coolant is captured by the first and second filter layers 16 and 17. You may make it change so that it may be easy to do. FIG. 10 is a side sectional view schematically showing the structure of the third filter layer 30 as the flow guiding means.

  As shown in FIG. 10, the third filter layer 30 includes a plurality of protrusions 31 provided so as to protrude toward the upstream side in the coolant flow direction (the lower side in FIG. 10), and the plurality of protrusions 31. The coolant inlet holes 32 are formed on the side surfaces of the first filter layer 16 and are provided in close contact with the upstream side of the first filter layer 16 in the coolant flow direction. At this time, the first filter layer 16 is arranged so that the longitudinal direction of the flow path 21 is perpendicular to the paper surface in FIG. 10 (note that the first filter layer 16 is not shown in FIG. 10). The third filter layer 30 itself can also remove foreign matters larger than the coolant inlet hole 32 from the inflowing coolant, and has a certain effect of separating the foreign materials from the coolant.

  With the third filter layer 30 having such a structure, the direction of flow of the cooling water passing through the third filter layer 30 is changed from a substantially vertical direction to a substantially horizontal direction as indicated by an arrow A in FIG. Then, it flows into the first filter layer 16 on the downstream side. Thereby, after changing the posture of the linear foreign matter mixed in the coolant so that its length direction is substantially perpendicular to the flow direction of the original coolant, as shown in D in FIG. It can be introduced into the first filter layer 16 on the downstream side. Therefore, even when the linear foreign matter flows in such a posture that its length direction is substantially parallel to the flow direction of the coolant, it can be reliably captured and the foreign matter separation performance can be improved. . When the third filter layer 30 is attached, the second filter layer 17 may be removed and only the first filter layer 16 may be used.

  Further, in the above-described embodiment of the present invention and the modifications thereof, the description has been given focusing on the trapping object as a linear foreign object. However, a foreign object other than the linear foreign object (for example, cutting waste or plate-like waste). ), Since they are generally larger in size than linear foreign objects, it goes without saying that they can be easily captured and removed from the coolant.

It is a sectional side view showing the whole fuel assembly structure provided with one embodiment of the lower tie plate of the present invention. It is a sectional side view which represents roughly the internal structure of one Embodiment of the lower tie plate of this invention. It is a top view showing the whole structure of the 1st filter layer which constitutes one embodiment of the lower tie plate of the present invention. It is a top view showing the whole structure of the 2nd filter layer which constitutes one embodiment of the lower tie plate of the present invention. It is a top view showing the grid | lattice-like flow-path area | region formed of the 1st and 2nd filter layer of one Embodiment of the lower tie plate of this invention. It is the conceptual diagram which compared the capture | acquisition state of the linear foreign material by the 1st and 2nd filter layer of one Embodiment of the lower tie plate of this invention, and the capture | acquisition means of the conventional structure. It is a top view which partially expands and represents the modification which deform | transformed the flow-path shape of the 1st and 2nd filter layer which comprises one Embodiment of the lower tie plate of this invention. It is a perspective view which expands and expresses partially the structure of the modification of the 1st and 2nd filter layer which comprises one Embodiment of the lower tie plate of this invention. It is the top view which expanded partially the structure of the modification of the 1st and 2nd filter layer which comprises one Embodiment of the lower tie plate of this invention, and was seen from the coolant flow direction. It is a sectional side view which represents roughly the structure of the 3rd filter layer which comprises the modification of one Embodiment of the lower tie plate of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel assembly 6 Lower tie plate 16 1st filter layer (capturing means; 1st capturing means)
17 Second filter layer (capturing means; second capturing means)
21 channel (first channel)
23 channel (second channel)
27 Thin plate 28 Spacer 30 Third filter layer (conducting means)
31 Projection 32 Coolant inlet hole

Claims (8)

In the lower tie plate of the nuclear fuel assembly,
A lower tie plate comprising a plurality of channels formed by being elongated and bent in a direction substantially perpendicular to the flow direction of the coolant, and having capturing means for capturing foreign matter in the coolant. In the lower tie plate of the nuclear fuel assembly,
A first capturing means comprising a plurality of first flow paths that are elongated and bent in a direction substantially perpendicular to the flow direction of the coolant;
A plurality of second flow paths elongated in a direction substantially perpendicular to the flow direction of the coolant and bent in a direction opposite to the bending direction of the first flow path; A lower tie plate, comprising: a second capturing means provided downstream of the means.   The lower tie plate according to claim 1 or 2, wherein a bent portion of the flow path or the first and second flow paths has an angular shape.   The lower tie plate according to claim 1 or 2, wherein a bent portion of the flow path or the first and second flow paths has a round shape.   The lower tie plate according to any one of claims 1 to 4, wherein the capturing means or the first and second capturing means are provided on a plurality of bent thin plates and the thin plates, respectively, and the thin plates are fixed. And a plurality of spacers for laminating at intervals of the lower tie plate.   The lower tie plate according to any one of claims 1 to 5, wherein a flow guide means for guiding the flow direction of the coolant in a direction substantially perpendicular to the flow direction is the capture means or the first capture means. A lower tie plate characterized by being provided in close contact with the upstream side.   The lower tie plate according to claim 6, wherein the flow guide means includes a plurality of protrusions provided so as to protrude toward the upstream side of the capture means or the first capture means, and the plurality of protrusions. A lower tie plate having a coolant inlet hole provided on each side surface. A fuel assembly comprising the lower tie plate according to any one of claims 1 to 7.

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