JP3161138B2 - Method of manufacturing fuel assembly and water rod - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel assembly, and more particularly to a fuel assembly suitable for use in a boiling water reactor to save nuclear fuel material.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. 63-73187 discloses a fuel assembly for reducing the flow rate of cooling water flowing through a reactor core at the beginning of a fuel cycle and increasing the flow rate of cooling water in the middle of the fuel cycle to effectively utilize nuclear fuel materials. 1 to 4 of FIG.
In this fuel assembly, as shown in FIG. 14 of JP-A-63-73187, a vapor layer is formed in a water rod at an early stage of a fuel cycle, and at the end of a fuel cycle, cooling water is formed in the water rod. To fill.

[0003] Further, Japanese Patent Application Laid-Open No. 63-73187 discloses FIG.
Next, a water rod having a cooling water rising pipe and a cooling water falling pipe and formed in an inverted U shape is illustrated. The cooling water riser and the cooling water descender are connected by a connecting pipe.

[0004]

In assembling the water rod in the above-mentioned conventional example, it is conceivable that the cooling water riser and the cooling water descender are joined to the connecting pipe by welding. When these are welded, for example, the cooling water riser pipe and the connection pipe are welded from the outside over the entire circumference, and then the welding between the cooling water descending pipe and the connection pipe is performed from the outside.

[0005] However, if the width of the gap between the cooling water riser and the cooling water descender is narrow, welding of the cooling water descender and the connecting pipe on the side of the cooling water riser cannot be performed. This is because the width of the gap between the cooling water riser and the cooling water descender is narrow, so that a welding torch or a welding rod cannot be inserted into the gap. Therefore, it is necessary to separate the cooling water riser and the cooling water descender to such an extent that the above welding is possible. This will increase the distance between the axial centers at both ends of the connecting pipe that individually joins the cooling water riser and the cooling water lowering pipe.

It is an object of the present invention to provide a simple and easy-to-use system, even when the width of the gap between the rising line of the water rod and its descending line is small.
It is an object of the present invention to provide a fuel assembly capable of forming a welded portion between a rising pipe and a descending pipe and a connecting member all around the rising pipe and the descending pipe.

Another object of the present invention is to provide a fuel assembly which can prevent a coolant rising passage from being blocked by solid matter in a rising line.

[0008] Another object of the present invention is to provide a fuel assembly that can further increase fuel economy.

[0009]

SUMMARY OF THE INVENTION In order to achieve the object of the present invention, a feature of the present invention is to provide a coolant rising passage for guiding a coolant supplied from a region below a fuel support of a lower tie plate upward. And a coolant descending passage which is located outside the ascending conduit and guides the coolant guided by the coolant ascending passage downward and discharges the coolant to a region above the fuel support portion. A fuel assembly including a water rod including a descending conduit provided therein, wherein one of the ascending conduit and the descending conduit is inserted into a coupling member and an upper end of the conduit is provided. Is welded to the coupling member, another pipe line is welded to a lower side of the coupling member, and a communication passage that communicates the coolant up passage and the coolant down passage with the coupling member. A lid member to be formed is attached to the coupling member. It is achieved by.

Another object of the present invention, provided the coolant up passage blocked tubular portion projecting upwardly into the riser passage disposed in the coolant rises passage, a side wall of the tubular portion This is achieved by the fact that the coolant rising passage above the tubular portion and the coolant rising passage below the tubular portion are communicated via the opening formed at the bottom.

Another object of the present invention is that the fuel spacer has a plurality of cylindrical members into which fuel rods are inserted, and the rising pipe is disposed in a region where the plurality of fuel rods can be disposed. The descending conduit is achieved by being arranged between a plurality of cylindrical members adjacent to the ascending conduit and adjacent to each other.

[0012]

One of the ascending conduit and the descending conduit is inserted into the coupling member, and the upper end of the conduit is welded to the coupling member, and the other conduit is welded to the lower side of the coupling member. Therefore, even when the width of the gap between the ascending conduit and the descending conduit is narrow, the welded portion between the ascending conduit and the descending conduit and the connecting member can be easily connected to the ascending conduit and the descending conduit. It can be formed over the entire circumference.

[0013] place the cold却材up passage blocked tubular portion protruding upward to the coolant rises in the passage provided in the rising pipe, from the tubular portion through an opening formed in the side wall of the tubular portion Since the upper coolant rising passage and the coolant rising passage below the tubular portion communicate with each other, solids in the coolant rising passage do not block the opening, and are located between the tubular portion and the rising pipeline. Settles in the formed area.

The ascending conduit is arranged in an area where a plurality of fuel rods can be arranged, and the descending conduit is arranged between a plurality of cylindrical members adjacent to the ascending conduit and adjacent to each other. Therefore, it is possible to increase the cross-sectional area of the coolant ascending passage in the ascending pipeline, and to increase the volume of the steam region in the coolant ascending passage and the coolant
The volume increases. As a result, changes in the void fraction described later
The effect of spectrum shift can be further improved because the width of the band becomes larger . This further increases fuel economy.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A fuel assembly according to a preferred embodiment of the present invention applied to a boiling water reactor will be described with reference to FIGS.

The fuel assembly 16 of this embodiment has a water rod 1, a fuel rod 17, an upper tie plate 18, a lower tie plate 19, and a fuel spacer 20. The upper and lower ends of the fuel rod 17 are held by an upper tie plate 18 and a lower tie plate 19. A plurality of fuel spacers 20 are arranged in the axial direction of the fuel assembly 16, and maintain a proper gap between adjacent fuel rods 17. The fuel spacer 20 is held by the water rod 1. The channel box 21 is attached to the upper tie plate 18 and surrounds the outer circumference of the bundle of fuel rods 17 held by the fuel spacer 20. The lower tie plate 19 has the fuel rod support 12 at the upper end and the fuel rod support 1
2 has a space 22 therein. Fuel rod support 12
Support the lower ends of the fuel rod 17 and the water rod 1.

The water rod 1 has a lower end plug 2, a rising pipe 3, a connecting portion 4, a downcomer pipe 5, and an upper end plug 6. The water rod 1 constituted by these components is made of a zirconium alloy.

The rising pipe 3 has a large-diameter pipe 3A and a large-diameter pipe 3A.
It has a small-diameter tube portion 3B and a tapered portion 3C whose outer diameter is smaller than that of the tube portion 3B. The tapered portion 3C has a through hole 7 inside and is tapered outside. The lower end of the large diameter tube portion 3A is welded to the upper end of the tapered portion 3C. The upper end of the small-diameter tube portion 3B is welded to the lower end of the tapered portion 3C.
The lower end of the small diameter tube portion 3B is joined to the lower end plug 2 by welding. The upper end of the large diameter tube portion 3A is joined to the connecting portion 4 by welding. The downcomer pipe 5 is arranged in parallel with the riser pipe 3, and the upper end thereof is joined to the connecting portion 4 by welding. The upper end plug 6 is attached to the upper end of the connecting portion 4.

FIG. 3 is an enlarged view of the lower end plug 2 in a state where the water rod 1 is held by the fuel support portion 12. The lower end plug 2 has a passage 2 </ b> A formed therein and a coolant inlet 9.
Is provided at the lower end of the lower end plug 2. Coolant inlet 9
Is provided on the side wall of the lower end plug 2 and communicates with the passage 2A. The lower end plug 2 has a protruding portion 2B having an upper end sealed at the upper end. The opening 10 is provided on the side wall of the protrusion 2B sideways. The protruding portion 2B is disposed concentrically with the small-diameter tube portion 3B in the small-diameter tube portion 3B, and is located above a welded portion between the small-diameter tube portion 3B and the lower end plug 2. For this reason, the clad reservoir 11 is formed annularly between the small-diameter tube 3 </ b> B and the lower end plug 2. The clad reservoir 11 is provided with the opening 10
It is located below.

The lower end plug 2 is inserted into a hole 32 formed in a boss 31 provided on the lower surface of the fuel support portion 12 of the lower tie plate 19. The lower end of the hole 32 is sealed. An opening 3 reaching the hole 32 is provided on the side wall of the boss 31.
3 are provided sideways. The outer diameter of the lower end plug 2 is
2 is substantially the same as the inside diameter. The lower end of the axially extending passage 2 </ b> A in the lower end plug 2 is closed by the bottom of the boss 31. In consideration of the fact that the water rod 1 grows by irradiation with the increase in the burnup of the fuel assembly, the opening 33 has a margin above the coolant inlet 9 of the lower end plug 2 so as to have a margin. It is preferable to use Further, the lower end plug 2 and the fuel support 1 are used for burning nuclear fuel and the like.
Considering that there is a possibility that the positional relationship with 2 may be different from that at the time of manufacturing, it is preferable that the opening 33 has a margin below the coolant inlet 9. Coolant rise passage 13
Are formed in the lower end plug 2 and the riser 3. That is, the coolant rising passage 13 includes the passage 2A, the opening 10, the space in the small-diameter tube 3B, the through hole, and the space in the large-diameter tube 3A. The coolant inlet 9 is located below the fuel support 12 and communicates with the space 22.

The downcomer 5 has a lower end hermetically sealed, and a discharge port 15 provided on a side wall of the lower end. The discharge port 15 is located above the fuel support 12. A coolant descending passage 14 is formed in the downcomer pipe 5. The discharge port 15 communicates with the coolant descending passage 14 and communicates with a coolant passage 23 formed between the fuel rods 17 above the fuel support portion 12.

As shown in FIG. 4, the connecting part 4 has a connecting part lower part 4A and a connecting part upper part 4B. The connecting portion lower portion 4A and the connecting portion upper portion 4B are joined by welding. Large diameter tube 3A
And the downcomer pipe 5 is welded to the connecting portion lower part 4A. The passage 24 formed in the connecting portion 4 connects the coolant rising passage 13 and the coolant descending passage 14. Therefore, the water rod 1
Has an inverted U-shape as shown in FIG.

29A is a welded portion between the lower portion 4A of the connecting portion and the riser 3; 29B is a welded portion between the lower portion 4A of the connecting portion and the descending tube 5;
Reference numerals 29C and 29C denote welding portions between the lower portion 4A of the connecting portion and the upper portion 4B of the connecting portion.

The fuel spacer 20 is, as shown in FIG.
It has a plurality of cylindrical round cells 25 arranged in a square lattice. The round cells 25 are mutually joined by welding. The round cell 25 has two rigid support portions 25A protruding inward. Elastic support members 26 are provided on adjacent round cells 25. Fuel rods 17 inserted into each round cell 25
It is supported at three points by two rigid support portions 25A and elastic support members 26.

Two water rods 1 and 1 a are inserted into the area formed between the round cells 25 at the center of the fuel spacer 20. The riser 3 of the water rod 1 and the riser 3a of the water rod 1a are located on one diagonal of the fuel spacer 20 and are arranged adjacent to each other. Down pipe 5 of water rod 1
Are round cells 25 adjacent to the riser 3 and located between the round cells 25E and 25F adjacent to each other. Similarly, the downcomer pipe 5a of the water rod 1a is a round cell 25 adjacent to the ascending pipe 3a and located between two adjacent round cells. Round cell 25 with downcomers 5 and 5a adjacent
Since the fuel rods 17 are arranged between the fuel rods 17, the outer diameter of each of the large-diameter tube portions 3 </ b> A of the water rods 1 and 1 a can be increased in a region where seven fuel rods 17 can be arranged. This leads to an increase in the cross-sectional area of the coolant rising passage 13 in the large-diameter tube portion 3A. Further, the downcomers 5 and 5a are located in directions opposite to each other in a direction of another diagonal line of the fuel spacer 20 which is orthogonal to the diagonal line where the ascending tubes 3 and 3a are located.

The riser 3 is provided on rigid support members 27A and 27B attached to a plurality of round cells 25 facing the riser 3 or the riser 3a, and a bridging member attached to the adjacent round cells 25. Elastic support member 28A-3
Supported by points. The riser 3a is supported at three points: rigid support members 27A and 27B and an elastic support member 28B provided on a bridge member attached to the adjacent round cell 25. The riser tube 3 and the riser tube 3a thus supported do not come into contact with each other.

The downcomer 5 (outer diameter of about 5 mm) is provided at a plurality of positions in the axial direction, though not shown, by a support member.
Is supported by the large-diameter tube portion 3A. A narrow gap is formed between the downcomer 5 and the large-diameter tube 3A. The downcomer pipe 5a is also supported by the large diameter pipe section 3A of the ascending pipe 3a.

The cross-sectional area of the coolant descending passage in the downcomer of the water rods 1 and 1a is smaller than 1/25 that of the coolant ascending passage (at the large diameter pipe section) in the ascending tube. Therefore, the fuel assembly 16 has characteristics as shown by the solid line in FIG. 15 and the solid line and the dashed line in FIG. 16 of JP-A-2-1590. The operation of the water reactor shown in FIG. 1 of the publication can be performed by adjusting the flow rate of cooling water supplied to the reactor core.

Coolant up passage 13 and coolant down passage 1
When the amount of cooling water supplied to the fuel assembly 16 provided with the water rods 1 and 1a having the water rods 4 therein is changed, the flow state of the fluid in the water rods 1 and 1a is described in 73
It changes as shown in FIGS. 14 (a), (b) and (c) of JP-A-187.

That is, the fuel assembly 16 is loaded in the core of a boiling water reactor. Although not shown, the flow rate of the cooling water supplied to the core is adjusted by controlling the rotation speed of the recirculation pump. The cooling water is first introduced into the space 22 of the lower tie plate 19. Most of this cooling water is supplied to the through holes 3 provided in the fuel support 12.
0, flows into the coolant passage 23 formed above the upper surface of the fuel support portion 12, and cools the fuel rod 17. The remaining part of the cooling water flows into the coolant rising passage 13 of the water rod 1 through the opening 33 and the coolant inlet 9. The same applies to the water rod 1a.

The flow of the fluid in the coolant rising passage 13 will be described. The cooling water guided to the passage 2A, which is a part of the coolant ascending passage 13, reaches the large-diameter tube portion 3A via the opening 10, the small-diameter tube portion 3B, and the tapered portion 3C. When the flow rate of the cooling water supplied to the fuel assembly 16 is small, the cooling water existing in the coolant ascending passage 13, particularly, in the large-diameter tube portion 3 </ b> A, is heated by irradiation of γ rays generated by nuclear fission of nuclear fuel. . When the flow rate of the cooling water supplied to the fuel assembly 16 is small, the cooling water becomes steam, and as shown in FIG. An area is formed. Therefore, a liquid level is formed in the coolant rising passage 13. The generated steam is
The liquid is discharged from the discharge port 15 into the coolant passage 23 through the passage 24 and the coolant descending passage 14. As the flow rate of the water supply increases, the liquid level in the coolant rising passage 13 rises and the steam area decreases, and eventually, FIG. 14 of JP-A-63-73187.
Finally, the state shown in FIG. 14C is reached after the state shown in FIG. 14B, that is, the state in which the coolant rising passage 13 and the coolant descending passage 14 are all filled with the cooling water. As a result, the variation width of the void fraction in the fuel assembly 16 can be increased between the initial stage and the final stage of the fuel cycle, so that the effect of the spectrum shift can be increased and the period of one fuel cycle can be greatly extended. it can. The state in which the coolant ascending passage 13 and the coolant ascending passage 14 are all filled with the cooling water is as follows.
Near the end of the fuel cycle, most of the fuel cycle forms a steam zone in the coolant riser passage 13. For this reason, when the coolant descending passage of the water rod is disposed so as to surround the coolant ascending passage as shown in FIG. The tube wall located between them comes into contact with the steam, resulting in insufficient cooling and high temperature. In this embodiment, the riser 3 and the downcomer 5 are arranged so as to form an inverted U-shape and the gap exists between the riser 3 and the downcomer 5 as described above. 5 is cooled by the cooling water rising around the cooling water passage 23. For this reason,
The temperatures of the riser 3 and the downcomer 5 are lowered.
The problem caused by the water rod shown in FIG.

As described above, the transition from the state in which the liquid surface is formed in the water rod 1 to the state in which the liquid surface is not formed by adjusting the flow rate of the cooling water supplied into the fuel assembly 16 is as follows. The fuel support portion 12 is in resistance to the cooling water passage 23, and the total cross-sectional area of all the through holes 30 provided in the fuel support portion 12 is set so that such liquid level movement is possible. Because there is. That is, the total cross-sectional area of all the through holes 30 is set corresponding to the hydrostatic head corresponding to the difference between the level of the upper end of the coolant ascending passage 13 and the level of the discharge port 15. The total cross-sectional area of all the through holes 30 provided in the fuel support portion 12 is
3 smaller than the cross-sectional area. The fuel support portion 12 having such a configuration acts as a resistance to the cooling water passage 23.

As described above, by disposing the downcomers 5 and 5a between the adjacent round cells 25, the large-diameter tube 3A is formed.
When the steam region is formed in the large-diameter pipe portion 3A, the amount of produced plutonium increases accordingly, and the coolant rising passage 13 and the cooling passage near the end of the fuel cycle are increased. When the inside of the material descending passage 14 is filled with the cooling water (moderator), the fission of fissionable materials including the plutonium is activated. Thereby, the reactivity at the center of the cross section of the fuel assembly 16 is further improved, and the nuclear fuel can be effectively used.
That is, the effect of improving fuel economy by the spectrum shift can be further increased. Since the downcomers 5 and 5a are located in directions opposite to each other in the direction of the other diagonal orthogonal to the diagonal where the risers 3 and 3a are located, even if the interior of the downcomers 5 and 5a is filled with steam, The regions can be arranged in a well-balanced manner without being locally concentrated in the cross section of the fuel assembly, and uneven combustion of nuclear fuel in the cross section of the fuel assembly can be prevented.

In the water rod shown in FIG. 4 of Japanese Patent Application Laid-Open No. 63-73187, one coolant inlet is provided at the lower end of the coolant rising passage. Therefore, the coolant inlet is
There is a possibility that solids such as cladding flowing along with the cooling water may block the cooling water. The smaller the diameter of the coolant inlet, the greater the probability. In this embodiment, the cooling water inlet 9 is provided so as to be perpendicular to the axial direction of the coolant ascending passage, and a plurality of cooling water inlets 9 are provided in the circumferential direction of the lower end plug 2. The cooling water flowing into the cooling water must be bent in a right angle direction just before that, and the probability that the plurality of cooling water inlets 9 will be blocked by cladding or the like is as shown in FIG. 4 of JP-A-63-73187. It is significantly smaller than a rod. Furthermore, since the cooling water inlet 9 is not provided in the axial direction of the lower end plug 2, since the lower end is closed, there is no opening in the core coolant flow direction, so that the effect of dynamic pressure due to the flow is suppressed. Therefore, the fluctuation of the liquid level in the water rod due to the fluctuation of the dynamic pressure can be remarkably suppressed.

As described above, a steam region is formed in the coolant rising passage 13 during most of the fuel cycle,
It is conceivable that the cooling water existing in the coolant rising passage 13 is concentrated, and the clad contained in the cooling water aggregates and sinks. The opening 10 is provided laterally and positioned above the bottom surface of the passage formed in the small-diameter tube portion 3B so that the opening 10 is not closed by the settling clad. The settled clad is gradually deposited in the clad reservoir 11 formed between the small-diameter tube portion 3B and the protruding portion 2B. The volume of the clad reservoir 11 is determined by assuming the amount of clad deposited during the life of the fuel assembly 16.

Next, a process of assembling the ascending pipe 3, the connecting portion 4 and the descending pipe 5 in this embodiment will be described with reference to FIG. The lower portion 4A of the connecting portion has through holes 4E and 4F as shown in FIGS. 6 (A) and 6 (D).
The upper end of the side wall between F and F is lower than the upper end of the formed lower portion 4A. The inner diameter of the through hole 4E is larger than that of the through hole 4F. FIG. 6D is a cross-sectional view of FIG.
It is X sectional drawing.

First, the rising pipe 3, that is, the upper end of the large-diameter pipe section 3A is provided over the entire circumference of the large-diameter pipe section 3A at the lower end of the side wall surrounding the through hole 4E of the connecting section lower part 4A having such a structure. It is attached by welding (FIG. 6 (A)). The lower connecting portion 4A and the large-diameter tube portion 3A are joined via a welded portion 29A. Then, the upper end of the downcomer 5 is connected to the through hole 4F in the lower part 4A of the connecting part.
And the side wall surrounding the through hole 4F of the lower portion 4A of the connecting portion and the entire periphery of the upper end of the downcomer pipe 5 are joined by welding from above (FIG. 6B). The lower part 4A of the connecting part and the downcomer pipe 5
9B. The connecting portion lower part 4A is a connecting member that connects the riser pipe 3 and the descender pipe 5 at their respective upper ends. Finally, the connecting portion upper portion 4B is connected to the connecting portion lower portion 4A.
It is installed on the lower part 4A of the connecting portion so as to cover the through hole 4E and the coolant descending passage 14 in the descending pipe 5. In such a state, the upper end of the lower part 4A of the connecting part is connected to the upper part 4B of the connecting part,
It is attached by welding over the entire circumference (FIG. 6 (C)). The connecting portion lower portion 4A is integrated with the connecting portion upper portion 4B via a welded portion 29C. The upper portion 4B of the connecting portion is a lid member that covers above the coolant rising passage 13 and the coolant descending passage 14. The upper end plug 6 is attached to the connection portion upper portion 4B by welding.

As described above, in the water rod 1 used in this embodiment, the downcomer 5 is inserted into the through hole 4F, and the upper end of the downcomer 5 is attached to the lower portion 4A of the connecting portion via the welding portion 29C. . Therefore, the entire circumference of the downcomer pipe 5 can be easily welded to the lower portion 4A of the connecting portion. Even if the width of the gap formed between the riser pipe 3, especially the large-diameter pipe part 3A and the downcomer pipe 5 is narrow, welding of the entire periphery of the downcomer pipe 5 to the lower portion 4A of the connecting portion can be easily performed. The downcomer 5 is arranged as shown in FIG. 5, and the width of the gap formed between the downcomer 5 and the large-diameter tube 3A cannot be made too large. When the width of the gap is increased, the outer diameter of the large-diameter tube portion 3A must be reduced.
This leads to a reduction in the cross-sectional area of the coolant ascending passage 13 in the large-diameter tube portion 3A, so that the above-described effect of the spectrum shift is reduced, and the degree of improvement in fuel economy is reduced. In FIG. 5, the downcomers 5 and 5a are:
Since a supporting structure member (not shown) that supports these on the corresponding large-diameter tube portion 3A collides with the adjacent round cells 25, the above-described arrangement position further places a gap formed between the adjacent round cells 25 in the gap formed between the adjacent round cells 25. It cannot be moved deep. In the welding structure of the large-diameter pipe 3A and the downcomer 5 and the lower part 4A of the connecting portion in FIG. 4 obtained by the assembling method in FIG. 6, the width of the gap between the large-diameter pipe 3A and the downcomer 5 is reduced. Thus, the outer diameter of the large-diameter tube portion 3A can be increased. For this reason, the cross-sectional area of the coolant rising passage 13 increases, and the degree of improvement in fuel economy due to the effect of the spectrum shift increases accordingly.

Incidentally, the water rod 1 receives an external force via the fuel spacer 20 during an earthquake or the like, so that a bending moment is generated in the water rod 1. In this embodiment,
The structural strength of the water rod 1 is dominated by the large diameter tube portion 3A. Therefore, from the viewpoint of soundness of the water rod structure, general welding of the large-diameter pipe portion 3A and the connecting portion lower portion 4A is preferable. Also,
As shown in FIG. 6 (C) of the present embodiment, with the lower end of the connecting portion lower portion 4A inserted inside the upper end portion of the large diameter tube portion 3A, welding of the large diameter tube portion 3A and the connecting portion lower portion 4A is performed. The size of the connecting portion lower portion 4A is larger than performing the welding of the large diameter tube portion 3A and the connecting portion lower portion 4A in a state where the connecting portion lower portion 4A surrounds the outside of the large diameter pipe portion 3A. Is small, and this is also good in terms of making the connecting portion 4 compact.

Water rods 1 and 1a used in this embodiment
The upper end of the lower tie plate 19 (the upper surface of the fuel support portion 12) is provided with the lower end plug 2 and the small-diameter tube portion 3B whose outer diameter is smaller than the large-diameter tube portion 3A. For this reason, the riser tube 3 has a smaller outer diameter near the lower end, that is, at a portion lower than the fuel spacer 20 arranged at the lowest level. The portion having a small outer diameter is 3 to 4% of the entire axial length of the water rods 1 and 1a. Water rods 1 and 1 upward from the upper surface of lower tie plate 19
a in the range of 3 to 4% of the total axial length of the water rods 1 and 1
By reducing the outer diameter of the riser 3 of (a), even when bending stress is applied to the riser 3 of the water rods 1 and 1a during an earthquake, generation of excessive stress at the lower end of the riser 3 is prevented. it can.

The riser 3 and the connecting portion 4 described in the above embodiment.
In addition to the assembling method of the downcomer 5 and the assembling method described below, even if the width of the gap formed between the large-diameter tube portion 3A and the downcomer 5 is small, the ascending tube 3 and the downcomer 5 are connected. It can be easily welded to the lower part 4A over the entire circumference.

The assembling method is such that the inner diameter of the through-hole 4E of the lower portion 4A of the connecting portion is made equal to the outer diameter of the large-diameter tube 3A of the riser tube 3, and the large-diameter tube 3A is inserted into the through-hole 4E. Diameter tube part 3
The upper end of A is welded to the lower portion 4A of the connecting portion. As shown in FIG. 6A, the downcomer 5 is welded to the above-mentioned side wall at the lower surface side of the lower portion 4A of the connecting portion with a part of the side wall surrounding the through hole 4F inserted into the downcomer as shown in FIG. The upper end of the connecting portion lower portion 4A is attached to the connecting portion upper portion 4B by welding over the entire circumference as shown in FIG. 6 (C). This first method is illustrated in FIG.
Compared with the case where the assembling method shown in FIG.
And the pressure loss of the fuel assembly increases. This is because the large diameter tube portion 3A is inserted into the through hole 4E,
This is because a side wall surrounding the through hole 4E is required. Further, the inner diameter of the through hole 4F becomes smaller than that of the downcomer 5.

In the assembling method shown in FIG. 6 and the above-described assembling method, the welding portions of the large-diameter tube portion 3A and the downcomer tube 5 to the connecting portion lower portion 4A are displaced in the axial direction. It has no adverse effect and does not hinder the insertion of the tube used for the other welding into the corresponding through-hole (connection lower part 4A).

FIG. 7 shows another embodiment of the lower end plug of the water rod used in the above embodiment. The lower end plug 2E closes the lower end of the lower end plug 2. That is, the passage 2A
Is closed at the lower end. The upper structure (not shown) of the lower end plug 2E is the same as that of the lower end plug 2. Lower end plug 2
E produces the same effect as the lower end plug 2. Further, by using the lower end plug 2E, the boss 31 is not required, and the structure of the lower tie plate 19 is simplified.

The lower end plug 2F shown in FIG. 8 manufactured by swaging the lower end plug 2 may be used. In this case, a round plate member for closing the passage 2 is attached to the lower end of the lower end plug 2F. Although not shown, lower end plug 2F
A projection 2B formed by the lower end plug 2 is attached to the upper part of the base. This lower end plug 2 also provides a lower end plug 2F
The same effect can be obtained.

FIG. 9 shows another embodiment of the lower end plug. The lower end plug 2G of this embodiment has an opening 9A of the passage 2A at the lower end.
Is provided. The configuration of the upper part of the lower end plug 2G is the same as the upper part of the lower end plug 2. The lower end plug 2G has an opening 9
A taper is formed outside the side wall surrounding the passage 2A near A. The formation of this taper can prevent the opening 9A from being clogged with a solid material such as a clad flowing together with the cooling water. However, since the opening 9A faces the flow direction of the cooling water, the effect of reducing the effect of the same pressure as in the opening 9 of the lower end plug 2 is small.

Another embodiment of the structure near the discharge port 15 of the downcomer pipe 5 is shown in FIG. In the embodiment shown in FIG. 1, a discharge port 15 is provided on the side surface of the downcomer pipe 5 in order to suppress the influence of dynamic pressure due to cooling water flowing outside the water rod. However, in terms of suppressing the effect of dynamic pressure due to coolant flow,
It is preferable to provide a plurality of openings 15A on the upper surface of the header 35 in which the lower end of the downcomer 5 is enlarged in an inverted conical shape as shown in FIG. The cooling water or steam that has descended in the coolant descending passage 14 flows out of the opening 15A along the flow direction of the cooling water in the coolant passage 23. in this way,
Since the direction of discharge of the fluid from the opening 15A and the direction of flow of the cooling water in the cooling water passage 23 are substantially the same, the discharge of the fluid from the opening 15A becomes smooth.

FIG. 12 shows another example of the structure near the discharge port of the downcomer 5 shown in FIG. In the present structural example, a header 35 </ b> A having an upper surface formed on the lower end portion of the downcomer pipe 5 and having a slope inclined outward from the replacement 5 is provided. The four openings 15 are formed on the upper inclined surface of the header 35A as in FIG.
B is provided.

FIG. 13 shows a water rod 1A which is another embodiment of the water rod 1 shown in FIG. This water rod 1A is provided with a support portion 36 extending downward at the lower end of the downcomer 5. This support 36 is inserted into the fuel support 12 of the lower tie plate 19. With such a structure, the supporting force of the downcomer 5 is increased, and the possibility that the downcomer 5 generates a flow vibration due to the cooling water flow flowing in the cooling water passage 23 is reduced. Since the irradiation growth amount of the fuel rod 17 by radiation is larger than that of the water rod 1A, the water rod 1A moves upward through the fuel spacer 20 according to the difference from the irradiation growth amount with the fuel rod 17. The lower end plug 2 of the riser 3 has a sufficient length so as not to fall out of the fuel support 12 by the above-mentioned upward movement during operation of the reactor.

[0050]

According to the present invention, one of the ascending conduit and the descending conduit is inserted into the coupling member, and the upper end of this conduit is welded to the coupling member to form another conduit. Is welded to the lower side of the connecting member, so that even when the width of the gap between the ascending conduit and the descending conduit is narrow, the weld between the ascending conduit and the descending conduit and the joining member can be easily formed. It can be formed over the entire circumference of the ascending pipeline and the descending pipeline.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a water rod used in the fuel assembly of FIG.

FIG. 2 is a longitudinal sectional view of a fuel assembly according to a preferred embodiment of the present invention.

FIG. 3 is an enlarged vertical sectional view of a lower end plug insertion portion of a water rod in the fuel support portion of FIG. 2;

FIG. 4 is an enlarged longitudinal sectional view of the vicinity of a connecting portion of the water rod in FIG. 1;

FIG. 5 is a plan view of the fuel spacer of FIG. 2;

FIG. 6 is an explanatory view showing a connecting step of welding a connecting portion of a water rod, and a rising pipe and a descending pipe.

FIG. 7 is a longitudinal sectional view of another embodiment of the lower end plug of the water rod.

FIG. 8 is a longitudinal sectional view of another embodiment of the lower end plug of the water rod.

FIG. 9 is a longitudinal sectional view of another embodiment of the lower end plug of the water rod.

FIG. 10 is a longitudinal sectional view of another structure near the lower end of the downcomer of the water rod.

FIG. 11 is a view taken in the direction of arrows XI-XI in FIG. 10;

FIG. 12 is a vertical sectional view of another structure near the lower end of the downcomer of the water rod.

FIG. 13 is a longitudinal sectional view showing the vicinity of a lower portion in another embodiment of the water rod.

[Explanation of symbols]

1, 1a: water rod, 2: lower end plug, 2B: protrusion,
3, 3a: rising pipe, 3A: large-diameter pipe part, 4: connecting part, 4A
... lower part of connecting part, 4B ... upper part of connecting part, 5, 5a ... downcomer,
9 coolant inlet, 10 opening, 11 clad reservoir, 12 fuel support, 13 coolant passage, 14
Coolant descending passage, 15 discharge port, 16 fuel assembly, 1
7 fuel rod, 18 upper tie plate, 19 lower tie plate, 20 fuel spacer, 22 space, 27A,
27B: rigid support member, 28A, 28B: elastic support member, 29A, 29B, 29C: welded portion, 30: through hole.

Continuing on the front page (72) Inventor Shozo Nakamura 502, Kandate-cho, Tsuchiura-shi, Ibaraki Pref. Machinery Research Laboratory, Hitachi, Ltd. (72) Inventor Satoshi Sugano 502, Kantate-cho, Tsuchiura-City, Ibaraki Pref. ) Inventor Koji Nishida 7-2-1, Omika-cho, Hitachi City, Ibaraki Prefecture Energy Research Laboratory, Hitachi, Ltd. (72) Inventor Yasunori Bessho 3-1-1, Sachimachi, Hitachi City, Hitachi, Ltd., Hitachi, Ltd. Hitachi Plant (72) Inventor Masatoshi Inagaki 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Osamu Yokomizo 7-2-1, Omika-cho, Hitachi City, Hitachi City, Hitachi Energy, Ltd. Research institute (72) Inventor Yuichiro Yoshimoto 3-1-1, Sakaimachi, Hitachi, Ibaraki Pref. Hitachi, Ltd. Hitachi Plant (56) References JP-A-3-179293 (JP, A) JP-A-2-249995 (JP, A) (58) key Field examined (Int.Cl. ⁷ , DB name) G21C 3/32 G21C 21/00

Claims (6)

(57) [Claims] 1. A lower tie plate having a fuel support;
A plurality of fuel rods having a lower end held by the fuel support,
A rising pipe having therein a coolant rising passage for guiding the coolant supplied from a region below the fuel support portion upward,
And a descending conduit having a coolant descending passage located outside the ascending conduit and guiding the coolant guided by the coolant ascending passage downward and discharging the coolant to a region above the fuel support portion. A fuel assembly comprising a water rod including: a pipe of one of the ascending pipeline and the descending pipeline is inserted into a coupling member, and an upper end of the pipeline is welded to the coupling member. The other pipe is welded to the lower side of the coupling member, a lid member that forms a communication passage between the coupling member and the coolant rising passage and the coolant descending passage, A fuel assembly attached to the coupling member. 2. The fuel assembly according to claim 1, wherein a coolant inlet for guiding coolant from a region below the fuel support portion into the coolant rising passage is provided on a side wall of the rising pipe. 3. The fuel assembly according to claim 1, wherein a cross-sectional area of the coolant descending passage is smaller than that of the coolant rising passage. Wherein provided in said rising pipe by placing the coolant up passage blocked tubular portion projecting upwardly into the coolant rises passage, an opening formed in a side wall of the tubular portion 2. The fuel assembly according to claim 1, wherein the coolant rising passage above the tubular portion and the coolant rising passage below the tubular portion are communicated with each other via a via. 5. A lower tie plate having a fuel support,
A plurality of fuel rods having a lower end held by the fuel support,
A fuel spacer for maintaining the spacing between these fuel rods,
A rising pipe having therein a coolant rising passage for guiding the coolant supplied from a region below the fuel support portion upward,
And a descending conduit having a coolant descending passage located outside the ascending conduit and guiding the coolant guided by the coolant ascending passage downward and discharging the coolant to a region above the fuel support portion. Wherein the fuel spacer has a plurality of cylindrical members into which the fuel rods are inserted, and the ascending conduit is capable of disposing a plurality of the fuel rods. arranged such region, the descending conduit, wherein disposed between the cylindrical member and a plurality of cylindrical member adjacent to the riser passage adjacent to each other, one of the rising pipe and the down pipe One of the pipes is connected
The upper end of the conduit inserted into the joint member is
And another pipeline is welded to the underside of the coupling member.
The coolant rising passage between the connecting member and the
Lid forming a communication passage communicating with the coolant descending passage
A material is attached to the coupling member.
Fuel assembly. 6. An ascending pipe having a coolant ascending passage therein for guiding the supplied coolant upward, and a coolant ascended outside the ascending duct and guided by the coolant ascending passage. Rod including a descending pipe having therein a coolant descending passage for guiding the fluid to a region above the fuel support portion
In the manufacturing method, one of the ascending conduit and the descending conduit is inserted into a coupling member, and an upper end of the conduit is welded to the coupling member, and the other conduit is coupled with the coupling member. A lid member welded to a lower side of the member and forming a communication passage connecting the coolant rising passage and the coolant descending passage with the coupling member, the lid member being attached to the coupling member. Rod manufacturing method.