JPH09304569A - Fuel spacer and lower tie plate and fuel assembly - Google Patents

Abstract

(57) [PROBLEMS] To reduce the flow resistance of the coolant flowing inside the fuel assembly and to improve the fuel limit output by the fuel spacer and the lower tie plate structure and their arrangement. Providing tie plates and fuel assemblies. In order to achieve the above object, a fuel spacer 27 according to the invention of claim 1 independently forms fuel rod insertion portions for inserting a plurality of fuel rods 2 and water rods 16 at substantially equal intervals. In a fuel spacer formed by arranging a plurality of cells in a substantially lattice pattern, a fuel rod 2 having a center of 4
A fuel rod insertion part 30 is formed between a plurality of cells 28 aligned with the center of the flow path between them and a support band 29 arranged on the outer periphery of the plurality of cells 28, and cooling is performed at the downstream end of the cells 28. A swirl vane 39 for guiding a material is integrally provided with a flow tab 42 at the downstream end of the support band 29.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel assembly of a nuclear reactor, and more particularly, to supporting a plurality of fuel rods and water rods in the fuel assembly at intervals.
The present invention relates to a fuel spacer and a lower tie plate that form a coolant passage, and a fuel assembly that uses the fuel spacer and the lower tie plate.

[0002]

2. Description of the Related Art As for a fuel assembly used in a boiling water reactor, as shown in a vertical sectional view of FIG. 17, a fuel assembly 1 has a plurality of fuel rods 2 arranged in a square lattice. The plurality of fuel spacers 3 arranged in the axial direction properly maintain the mutual spacing. Further, the plurality of fuel rods 2
An upper tie plate 5 provided with a handle 4 is provided at the upper part of the above and a lower tie plate 6 is fixed at the lower part to form a fuel bundle, and the fuel bundle is inserted into a channel box 7 of a rectangular cylinder. To do.

Water, which is a coolant, flows from the lower tie plate 6 of the fuel assembly 1 in the direction indicated by the white arrow 8, and is taken out from the upper tie plate 5 as high-temperature steam by the nuclear thermal reaction of the fuel rods 2 inside. ing. As the conventional fuel spacer 3, the plan view of FIG.
As shown in the partially cut-away side view of (b), there is a lattice type fuel spacer 11 in which the strip-shaped plate 9 is assembled in a square lattice shape and the outer periphery thereof is surrounded by a square frame-shaped support band 10.

Further, as shown in the plan view of FIG. 19, cylindrical metal cells 12 having a diameter equal to the arrangement pitch of the fuel rods 2 are arranged in a square frame-shaped support band 10 in a square lattice shape, A round cell type fuel spacer 13 in which the above is joined is known. Therefore, hereinafter, the fuel spacer shown in FIG. 18 will be referred to as a lattice type fuel spacer 11, and the fuel spacer shown in FIG. 19 will be referred to as a round cell type fuel spacer 13.

The grid type fuel spacer 11 has lantern type springs 14 attached to every other intersection of the square lattice-shaped strip-shaped plates 9 and a supporting member for the strip-shaped plates 9 without the lantern-type springs 14 attached. 15 is provided to support the fuel rod 2 and the water rod 16 which are inserted into the lattice formed by the strip plate 9 together with the lantern type spring 14. An outer protrusion 17 that abuts the channel box 7 (not shown) is projected on the outer periphery of the support band 10.

Further, in the round cell type fuel spacer 13, the fuel rods 2 are inserted into the respective cylindrical metal cells 12 which are independent of each other. The fuel rods 2 are supported inside the metal cells 12. This is performed by the protruding small protrusion 18 and the spring restraining body 19 that joins the adjacent metal cells 12 together.
A large water rod 20 is inserted through the central portion.

The lattice type fuel spacer 11 and the round cell type fuel spacer 13 keep the fuel rods 2 arranged in the channel box 7 at a predetermined distance from each other as described above and are excited by the flow of the coolant. It is provided with a function of suppressing the fluid vibration of the fuel rods 2 that is generated.

On the other hand, since the lattice type fuel spacer 11 and the round cell type fuel spacer 13 are located between the fuel rods 2 which are coolant passages due to their shapes, they obstruct the coolant passage. Since it becomes a substance, it acts as a flow resistance of the coolant. Generally, the flow resistance in a fluid is several times larger under the two-phase flow condition in which water and steam are mixed and flows at a higher speed than in water single-phase flow. Inside the fuel assembly 1 of the flowing boiling water reactor,
The ratio of the fuel spacer 3 to the flow resistance in the fuel assembly 1 is as large as about 20%.

The pressure loss in the fuel assembly 1 is an important factor in designing the capacity of the coolant circulation pump for circulating the coolant through the core formed by the plurality of fuel assemblies 1 and the control rods (not shown). Therefore, the reduction of the pressure loss in the fuel spacer 3 leads to the reduction of the capacity of the coolant circulation pump. Further, the increase in the flow resistance in the fuel spacer 3 adversely affects the stability of the coolant flow at a low flow rate such as natural circulation, and further, the fuel assembly 1
It also affects the limit output of.

Therefore, among the constituent parts of the fuel assembly 1, the fuel spacer 3 has a great influence on the pressure loss characteristics when the coolant flows in the fuel assembly 1, and the stability and cooling characteristics of the fuel are improved. But it is an important part. Particularly during normal reactor operation, reducing the power of the coolant circulation pump that sends the coolant to the fuel assembly 1, that is, improving the pressure loss characteristics of the fuel spacer 3, directly improves the power generation efficiency of the nuclear power plant. In order to be involved in the above, a proposal for reducing the pressure loss in the fuel spacer 3 has been conventionally made.

For example, a round cell type fuel spacer shown in FIG.
In No. 13, a plurality of cylinders having a diameter corresponding to the fuel rod pitch are arranged vertically and horizontally, and adjacent outer sides are joined together.

Therefore, the lattice type fuel spacer 11 shown in FIG.
As shown in FIG.
Located in the center between each fuel rod 2, which is a coolant channel,
In addition, the small projections 18 of the member supporting the fuel rods 2 and the spring restraining members 19 are closer to the fuel rods 2 than those in which the lantern type springs 14 are also arranged, and the respective fuel rods 2 are formed mutually. Since there is no member that obstructs the flow of the coolant in the center of the space, the pressure loss is low.

In the case of the lattice type fuel spacer 11,
As shown in the iso-steam flow velocity diagram of FIG. 20, as the flow of the coolant in the fuel assembly 1, the steam flows at high speed between the fuel rods 2, and the water in the liquid phase has an average thickness on the surface of the fuel rods 2. 0.2 mm
It flows as a thin liquid film 21 of about 0.6 mm. As a result, the vapor flow velocity in the space between the fuel rods 2 has the lowest distribution in the low flow velocity portion 22 on the surface of the fuel rods 2 and the highest in the high flow velocity portion 23 in the center between the fuel rods 2.

Taking the case where there is no obstacle in the coolant passage as an example, the flow velocity becomes slow on the wall surface of the fuel rod 2, and the flow resistance R is usually expressed by the following equation (1). The fluid velocity V squares the flow resistance R, where S is the projected area on a plane perpendicular to and the fluid density is ρ.

[0015] R = CD × S × ρ × V 2/2 ... (1) As the means for limiting the output increase in the fuel assembly 1 conventionally been proposed devised for the third from the first of the following There is. First, the liquid film 21 on the inner surface of the unheated channel box 7 that does not contribute to the cooling of the fuel rods 2 is stripped off and utilized for cooling the fuel rods 2 arranged near the channel box 7.

To this, a plate called a flow scraper or a flow skirt is attached to the fuel spacer 3 and brought into contact with the inner wall of the channel box 7, so that the liquid film 21 that propagates along the inner wall of the channel box 7 is peeled off. Let The separated water should be scattered into the main stream from the downstream end of the support band 10 which is the outer frame of the fuel spacer 3 or a claw-shaped projection called a flow tab provided at the downstream end, and adhere to the surrounding fuel rods 2. This improves the cooling effect of the fuel rod 2.

As shown in the schematic view of FIG. 21, the second is included in the main steam flow by attaching a twist plate 24 or swirl vanes to the flow passage space surrounded by the fuel rods 2 on the downstream side of the fuel spacer 3. The droplet 25 directed toward the fuel rod 2 is generated by the swirling flow 26 generated by the twist plate 24 or the swirl vane, or the centrifugal force acting on the liquid film 21 attached to the surface of the twist plate 24 or the swirl vane. Is used to improve the cooling of the fuel rods 2.

Third, the fuel bundle and the channel box 7
It is to keep the central axes of the same as much as possible.
The distance between the fuel bundle and the channel box 7 is set so as not to be less than a predetermined distance by the outer protrusion 17 provided on the support band 10 of the fuel spacer 3.

However, since a play necessary for assembling the fuel assembly 1 is provided between the outer side of the fuel spacer 3 and the inner side of the channel box 7, the fuel bundle inside the channel box 7 is provided. Fuel rods 2 arranged on the outermost periphery facing the channel box 7 in a biased state
, There is a possibility that the spacing between the channel box 7 and the channel box 7 is not uniform.

For this reason, there is a concern that the flow of the coolant will deteriorate in a narrow passage and the cooling capacity will decrease. Therefore, in order to reduce the unevenness of the spacing as much as possible, the fuel spacer 3 and the channel box 7 are required. It has been proposed to provide a spring (not shown) between them and to absorb the play between the channel box 7 and the fuel spacer 3 by thermal expansion.

[0021]

Conventional fuel spacer 3
In the above-mentioned lattice type fuel spacer 11, the flow resistance is large because the strip-shaped plates 9 intersecting the central spaces of the fuel rods 2 having a high flow velocity and the members such as the lantern type spring 14 are present.

As a countermeasure against this, by projecting each member in a mountain shape in the flow direction of the coolant, abrupt changes in the flow passage area due to the members are eliminated, and the flow resistance is alleviated and the pressure loss in the fuel spacer is reduced. A device has been devised. However, when the pressure loss of the fuel spacer 3 in the fuel assembly 1 is reduced, there is a problem that the limit output also decreases.

In addition, as a method of reducing the flow resistance of the fuel spacers 3, the thickness of the member parallel to the flow direction of the coolant is reduced or partially removed so that the flow of the coolant is perpendicular to the flow direction. Some reduce the flow resistance by reducing the projected area of the directional member. As described above, the device for reducing the pressure loss in the fuel spacer 3 has been conventionally made, but in the round cell type fuel spacer 13, a plurality of cylindrical metal cells 12 having a constant diameter corresponding to the fuel rod pitch are used.
Is circumscribed and the fuel rod 2 is inserted inside.

For this reason, the member cannot be brought close to the vicinity of the fuel rod having a low vapor flow velocity, and the metal cell 12 is provided in the flow path between the fuel rod 2 and the channel box 7 arranged at the outermost periphery. Since the supporting band 10 and the cell member to be bundled are formed in double, the projected area of the member in the direction perpendicular to the flow of the coolant becomes large, and the effect of sufficiently reducing the pressure loss cannot be obtained.

As a device for improving the limit output of the fuel assembly 1, a twist plate 24 is provided downstream of the fuel spacer 3.
Alternatively, although swirl vanes have been devised, when applied to the lattice type fuel spacer 11, the central axis of the twist plate 24 or swirl vanes should be located in the center of the space formed between the fuel rods 2. Therefore, the member of the twist plate 24 is provided downstream of the axis where members such as the strip plate 9 intersect.

For this reason, the coolant is at the high flow velocity portion 23 in the region of the highest vapor flow velocity in the center of the space between the fuel rods 2,
Since it is decelerated by the members of the twisted plates 24 that intersect,
The effect of the twist plate 24 or the swirl vanes is not sufficiently exerted, and therefore, the effect of improving the limit output in the fuel assembly 1 is limited to some extent.

Further, a device for providing a swirl vane (twisting vane) at the downstream end of the round cell type fuel spacer 13 is disclosed in, for example, Japanese Unexamined Patent Publication No.
-230163, "Fuel Spacer and Fuel Assembly". However, since this torsion blade is installed between four tubular ferrules (metal cells) through which fuel rods are inserted, if the joint of the torsion blade undergoes fatigue failure during reactor operation, these fragments will enter the coolant. It is conceivable that the mixed fuel may damage the fuel cladding tube (not shown) on the surface of the fuel rod 2 and other devices.

It should be noted that the twisted blade may be cut out from the member of the tubular ferrule, but in this case, the size of the twisted blade is limited by the dimension of the member of the tubular ferrule, and the degree of freedom in design is reduced. It was

When the twist plate 24 or the swirl vanes are attached to the fuel spacer 3, the fuel rod 2 arranged in the central portion has four sets of the twist plate 24 or swirl vanes around the fuel rod 2. The effect of improving the limit output is great. However, in the fuel rod 2 arranged at the outermost periphery, it is difficult to provide the twist plate 24 or the swirl vane on the channel box 7 side. Therefore, the twist plate 24 or the swirl vane 2 is provided around the fuel rod 2. Since only a set is provided, there is a problem that the effect of improving the limit output in the fuel assembly 1 is small.

As for the thermo-hydraulic device for fuel, many devices for the fuel spacer 3 have been devised. In particular, the two-phase flow flow mode in the axial direction, which is a characteristic of boiling water reactors, is used. In consideration of the change, the fuel spacers 3 arranged in the axial direction, and further, a device for improving the thermo-hydraulic force and the nuclear force to obtain a comprehensive effect including the lower tie plate 6 has not been made.

The object of the present invention is to reduce the flow resistance of the coolant flowing inside the fuel assembly due to the structure of the fuel spacer and the lower tie plate and the arrangement thereof, and to improve the fuel limit output. To provide a spacer and a lower tie plate and a fuel assembly.

[0032]

In order to achieve the above object, a fuel spacer according to a first aspect of the invention has independent fuel rod insertion portions for inserting a plurality of fuel rods and water rods at substantially equal intervals. In a fuel spacer formed by arranging a plurality of cells to be formed in a substantially lattice shape, a plurality of the cells whose center coincides with the center of the flow path between the four fuel rods and a support arranged on the outer periphery of the plurality of the cells. The fuel rod insertion part is formed between the band and the swirl vane for guiding the coolant to the downstream end of the cell, and a flow tab is integrally provided at the downstream end of the support band.

With the central axis of the flow passage surrounded by four fuel rods in the fuel assembly as the center of the cell, no member or the like is arranged in the region near the center of the flow passage where the coolant vapor velocity is high. Therefore, the flow resistance is low. Further, since a swirling flow is generated in the steam by the swirl vanes that guide the coolant formed integrally with the member, the droplets in the steam adhere to the fuel rods due to the centrifugal force, and the fuel limit output increases.

Further, since the coolant flowing in the outermost circumference is directed to the fuel rod located in the outermost circumference of the fuel assembly by the flow tab of the support band, the limit output in the outermost fuel rod is improved.

A fuel spacer according to a second aspect of the present invention is characterized in that a swirl vane for guiding a coolant is integrally provided at a downstream end of a support band forming a fuel spacer together with a cell. Since the coolant flowing in the outermost periphery is directed to the fuel rods located in the outermost periphery of the fuel assembly by the swirl vanes that guide the coolant of the support band, the limit output of the fuel rods in the outermost periphery is further improved.

In a fuel spacer according to a third aspect of the present invention, a fuel contact portion and a spring for supporting a fuel rod are integrally formed with the cell and the support band at a fuel rod insertion portion formed between the cell and the support band. It is characterized by being provided. The fuel rod inserted into the fuel rod insertion portion formed of the cell and the support band is supported by the fuel contact portion and the spring having a structure with low flow path resistance. In addition, the members of the cells and the support band, the fuel contact portion, and the spring are integrated so that the structure is firm.

A fuel spacer according to a fourth aspect of the invention is characterized in that the cell and the support band are cut out from the respective members and the ends are fixed after bending. Since the cell and the supporting band have simple structures, they are solid and easy to manufacture.

A fuel spacer according to a fifth aspect of the present invention is characterized in that, in the cell and the support band, the projections that come into contact with the adjacent cells and the support band are provided with alignment protrusions or alignment recesses to be assembled with each other. To do.
When manufacturing a fuel spacer by combining multiple cells and support bands, by fitting the alignment protrusions and alignment recesses provided on each other's protrusions, the work is simple and they are fixed by welding, etc. Will also be easier.

In the fuel spacer according to a sixth aspect of the present invention, the fuel abutting portion for supporting the fuel rod in the fuel rod insertion portion is cut out from the cell and the member of the support band and bent, and then the free end is formed into the cell. It is characterized by being fixed to. Since the members of the cell and the support band and the member of the fuel contact portion are integrated, the structure is solid and there is no waste of material, and manufacturing is easy.

In the fuel spacer according to the seventh aspect of the invention, the spring supporting the fuel rod in the fuel rod insertion portion cuts out from the member of the cell and the supporting band and bends the member and the member integrated side with the coolant flow. It is characterized by being on the upstream side of the road. Since the member of the cell and the support band and the member of the spring are integrated, the structure is solid and there is no waste of material. Further, since the upstream side of the spring is integrated with the cell, the droplets or liquid film flowing with the vapor from the upstream side are easily guided to the surface of the fuel rod along the spring.

In a fuel spacer according to an eighth aspect of the present invention, a ferrule cell into which a plurality of fuel rods and water rods are independently inserted is arranged in a lattice pattern at substantially equal intervals, and a support band is arranged on the outer periphery. In the spacer
An extension portion is provided inside the fuel assembly at the downstream end of the ferrule cell arranged on the outermost periphery, and a plurality of flow tabs are provided at the downstream end of the support band.

The coolant flowing to the outermost periphery in the fuel assembly is
The flow tab of the support band guides the fuel rod and the extension of the ferrule supporting the fuel rod, and the coolant is directed to the outermost fuel rod without splashing inside the fuel assembly.

In the fuel spacer according to the ninth aspect of the present invention, the extension portion provided inside the fuel assembly at the downstream end of the ferrule cell is made to project downstream from the ferrule cell located in the central portion of the fuel assembly. It is characterized by The coolant flowing in the outermost periphery of the fuel assembly, which is directed by the flow tab of the support band, is collected in the extension portion of the ferrule cell, and thus is efficiently guided to the fuel rods in the outermost periphery.

A fuel spacer according to a tenth aspect of the present invention is characterized in that the flow tab provided at the downstream end of the support band is inclined inside the fuel assembly in a curved or bent cross section. Since the flow tab of the support band has a curved or bent cross section and its tip faces the upstream side, the coolant guided by this flow tab is located at the upstream side of the extension of the outermost fuel rod and ferrule cell. Is efficiently collected and guided to the outermost fuel rods.

The lower tie plate according to the invention of claim 11 is a lower tie plate of a fuel assembly for fixing the lower portions of a plurality of fuel rods and water rods arranged in a grid at substantially equal intervals. A plurality of plate-shaped projections that are inclined with respect to the flow direction of the coolant are provided at the downstream end at the outermost circumference, and the circumferential lengths of the projections projected in the vertical direction monotonically change along the downstream end and are adjacent to each other. The change in the circumferential length is the same between the protrusions.

The coolant that has passed through the lower tie plate is agitated by a swirling flow generated in one direction due to a plurality of protrusions provided on the outermost periphery of the lower tie plate for redistributing the flow rate and the inclination and the changing direction of the circumferential length. To be done. As a result, the peripheral flow rate of the coolant on the downstream side of the lower tie plate increases, and the temperature becomes uniform, so that it flows into the flow path formed between the fuel rods in the channel box, and low voids are generated. The distribution of voids in the rate region is flattened.

A lower tie plate according to a twelfth aspect of the present invention is characterized in that a plurality of protrusions provided at the outermost periphery of the lower tie plate at the downstream end incline the base line of inclination with respect to the flow of the coolant from the horizontal line. To do. The size of the swirling flow can be easily changed by inclining the inclined base line of the protrusion provided at the downstream end of the lower tie plate from the horizontal line. Therefore,
By changing the magnitude of this swirl flow, the function of redistributing the flow rate of stirring the coolant on the downstream side can be appropriately designed.

A fuel spacer according to a thirteenth aspect of the present invention is the fuel spacer in which a plurality of fuel rods and water rods whose upper and lower parts are fixed by an upper tie plate and a lower tie plate are arranged and supported in a lattice pattern at substantially equal intervals. A plurality of plate-shaped projections inclined to the flow direction of the coolant are provided at the downstream end at the outermost periphery of the fuel spacer, and the circumferential length of the projections projected in the vertical direction changes monotonically along the downstream end. The change in the circumferential length is the same between adjacent protrusions.

The coolant flowing inside the fuel assembly is agitated by the swirling flow generated by the projections that redistribute the flow rate, on the downstream side of the fuel spacer arranged in the middle of the flow path,
Increase the peripheral flow rate and make the temperature uniform.

A fuel spacer according to a fourteenth aspect of the present invention is characterized in that a plurality of protrusions provided at the outermost periphery of the fuel spacer at the downstream end incline a base line of inclination with respect to the flow of the coolant from the horizontal line. The size of the swirling flow can be easily changed by inclining the inclined base line of the projection provided at the downstream end of the fuel spacer from the horizontal line. Therefore, by changing the magnitude of the swirling flow, it is possible to appropriately design the function of redistributing the flow rate for stirring the coolant on the downstream side.

The fuel assembly according to the invention of claim 15 is
A plurality of projections that are inclined with respect to the flow direction of the coolant are provided at the downstream end at the outermost circumference, and the circumferential length projected by the projections in the vertical direction monotonically changes along the downstream end, and the circumference between adjacent projections is increased. It is characterized in that the fuel spacers having the same length change direction are arranged near the lowermost end of the effective heat generating portion in the fuel assembly.

In the vicinity of the lowermost end of the effective heat generating portion of the fuel assembly, the void ratio of the coolant is low and the temperature is non-uniform.
The function of the protrusions for redistributing the flow rate of the fuel spacer arranged at this position flattens the voids and the temperature distribution of the coolant on the downstream side.

The fuel assembly according to the invention of claim 16 is
In a fuel assembly in which a plurality of fuel rods and water rods are arranged between an upper tie plate and a lower tie plate, a plurality of fuel spacers are arranged in the axial direction, and the center of the fuel assembly is inserted into a rectangular tubular channel box. A fuel rod insertion part is formed between a plurality of cells aligned with the center of the flow path between the rods and a support band arranged on the outer periphery thereof, and a swirl vane is provided at the downstream end of the cells and a flow tab is provided at the downstream end of the support band. The fuel spacers integrally provided with the ferrule cells which are arranged at the above-mentioned approximately equal intervals in a lattice shape and through which a plurality of fuel rods and water rods are independently inserted and which are arranged at the outermost periphery. A fuel spacer having a plurality of flow tabs at the downstream end of the support band arranged on the outer periphery and a plurality of plate-shaped projections at the downstream end of the outermost periphery are provided together with the extension portion. Peripherals projected in the vertical direction of the protrusions change monotonously along the downstream end, and the change in peripheral length is the same between adjacent protrusions.The lower tie plate and the fuel spacer, etc. are individually or appropriately combined. It is characterized by being provided by.

By forming a low flow resistance without disposing an obstacle such as a member in the flow path of the coolant, and sufficiently guiding the coolant to the fuel rods supported by the swirl vanes, the limit output of fuel is improved. A fuel spacer or a fuel spacer for guiding the coolant flowing to the outer peripheral portion to the fuel rods arranged on the outermost periphery of the fuel assembly to improve the limit output of fuel is arranged.

Further, the protrusions for redistributing the flow rate of the coolant agitate the coolant on the downstream side to increase the outer peripheral flow rate and equalize the temperature, thereby flattening the voids and the temperature distribution. By appropriately combining a single type or a plurality of types, etc., a fuel assembly having respective characteristics can be obtained.

[0056]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings. Note that the same components as those of the above-described related art are denoted by the same reference numerals, and detailed description thereof will be omitted. The first embodiment relates to claims 1 to 7 and claim 16, and FIG. 1 is a transverse cross-sectional view of a main part of a fuel assembly.
Is a perspective view of the cell, and FIG. 3 is a perspective view of a main part of the support band. Note that FIG. 2A is a side view of the fuel supporting protrusion, FIG.
3B and FIG. 3A and FIG. 3B are perspective views of the spring side.

The fuel spacer 27 has a plurality of cells 28 shown in FIG. 2 arranged therein in an approximately lattice shape and joined together, and a support band 29 shown in FIG. To the outside of four adjacent cells 28, or to the outside of one or two cells 28 and the support band 29, respectively.
A fuel rod insertion portion 30 for independently supporting and inserting a plurality of fuel rods 2 at substantially equal intervals is formed on the inner side of (1) (claim 1).

Further, the fuel insertion portion 30 of the fuel spacer 27
The fuel rods 2 and the water rods 16 are inserted into the above, and the upper and lower parts of the fuel rods 2 etc. are fixed by an upper tie plate 5 and a lower tie plate 6 not shown to form a fuel bundle, and the fuel bundle is formed in the channel box 7. The fuel assembly 31 is constructed by being inserted into the inside (claim 16). The fuel spacer
Both the cell 28 and the support band 29 constituting 27 are formed by bending using a plate-like material having a spring property such as Inconel and having strong corrosion resistance (claim 4).

The cell 28 has a cross-shaped cylindrical shape as shown in FIG. 2, and at the tip of each protruding portion 32, a positioning convex portion 33 is provided for positioning when the adjacent cells 28 are combined and combined.
And an alignment recess 34 is formed. Also, each cell 28
The intermediate portion 35 of each of the protrusions 32 is a portion forming the fuel rod insertion portion 30 on the outer side thereof, and the fuel contact portion 36 and the spring 37 for supporting the inserted fuel rod 2 are provided in a protruding manner. (Claim 5).

As shown in FIG. 2 (a), the fuel contact portion 36 is cut out into a plate shape on both sides in a state where it is integrated with the member of the cell 28 and one of which is connected to the cell member, and is projected by bending. After molding, the cut-out tip portion is welded again 38 to the cell member to be formed (Claim 6). Also, the spring 37
2B, as shown in FIG. 2B, with the member of the cell 28 integrated with the cell member on the upstream side in the coolant flow direction indicated by the white arrow 8, the sheet is cut out into a plate shape and formed by bending. (Claim 7).

Furthermore, four intermediate portions 35 in each cell 28 are provided.
At the downstream end, a swirl vane 39 formed integrally with the cell member is formed inward, and is provided so as to guide the coolant from the upstream side to the outside (claim 1). The cell 28 has a cell member, a fuel contact portion 36, a spring 37, and a swirl vane 39 integrated with each other, and a plurality of cells 28 are combined by associating mutually protruding portions 32 with each other, and arranged in a substantially lattice shape. Then, by welding, the central portion of the fuel spacer 27 shown in FIG. 1 is formed (claim 3).

As shown in FIG. 1, in the outer peripheral portion of the fuel spacer 27, the fuel rod insertion portion 30 for supporting the fuel rods 2 arranged at the outermost periphery cannot be formed only by the cells 28. The fuel spacer 27 is constructed by combining the support bands 29 shown in FIG.

As shown in FIG. 3 (a), the support band 29 is in the form of a strip and has a protrusion 40 for abutting the protrusion 32 of the cell 28 on the inside and a bathtub 41 for abutting the channel box 7 on the outside. A flow tab 42 bent inward is provided at the downstream end of the bathtub 41 (claim 1). Further, the intermediate portion 43 between the bathtub 41 and the protruding portion 40 is provided with a fuel contact portion 36 and a spring 37 which are protruded inward to support the fuel rod 2 and are integrated with the member (claim). 3).

Regarding the straight portion of the fuel spacer 27 in the support band 29, the intermediate portion 43 provided with the spring 37 and the intermediate portion provided with the bathtub 41 and the fuel contact portion 36 are provided between the protrusions 40. 43 are arranged. Further, in the corner portion of the fuel spacer 27, an intermediate portion 43 provided with a spring 37 and a bathtub 41 are provided between the protruding portions 40 and 40, and an intermediate portion 43 provided with the fuel contact portion 36 and a bathtub 41, and The intermediate portion 43 provided with the fuel contact portion 36 is arranged.

The support band 29 is shown in FIG.
As shown in (b), there is also a structure in which a swirl vane 39 is integrally provided at the downstream end of the intermediate portion 43 (claim 2). Further, in order to continuously form the support band 29, it is possible to easily increase the length by appropriately connecting a plurality of pieces divided according to the material measurement thereof by welding or the like.

Next, the operation of the above configuration will be described. In the fuel spacer 27, a plurality of cells 28 are arranged in a substantially lattice pattern in the central portion occupying most of the fuel spacer 27,
The outer peripheral portion is surrounded by a support band 29 to form a substantially square shape. Regarding the central portion, a fuel rod insertion portion 30 for inserting the fuel rod 2 is formed outside the four adjacent cells 28, and the linear portion of the outer peripheral portion is the outside of the two cells 28 and the support band 29.
Inside, and the corner portion forms the fuel rod insertion portion 30 outside the one cell 28 and inside the support band 29.

The fuel rod 2 inserted into each of the fuel rod insertion portions 30 has a fuel contact portion 36 and a spring 37 protruding from four directions.
The fuel rods 2 are surely supported by, and the fuel rods 2 are arranged in a substantially square lattice shape while maintaining a predetermined gap therebetween.

In the fuel spacer 27 in which the fuel rods 2 are arranged, a coolant passage is formed between the center of the cell 28 and the fuel rod 2 of the fuel rod insertion portion 30, and at the center of the cell 28. The coolant flow channel coincides with the center of the coolant flow channel between the four fuel rods 2, and no member that blocks the flow of the coolant is arranged in this coolant flow channel, so that the flow resistance is low. As a result, it is easy to reduce the capacity of the coolant circulation pump and the like, and the operation efficiency in the nuclear power plant is improved.

Further, a swirl vane is provided at the downstream end of the cell 28.
39 is integrally formed, and a flow tab 42 is integrally formed at the downstream end of the bathtub 41 in the support band 29. The swirl vane 39 and the flow tab 42 are both bent toward the fuel rod 2. Has been.

Therefore, the coolant flowing through the coolant passage in the fuel assembly is scattered toward the nearest fuel rod 2 by the swirl vanes 39 and the flow tabs 42 in the fuel spacer 27. The scattered droplets 25 (not shown) are efficiently directed to the fuel rods 2 and thus effectively contribute to the improvement of the fuel limit output.

Further, according to the supporting band 29 provided with the swirl vanes 39 shown in FIG. 3B, it is formed between the two fuel rods 2 in the outer peripheral portion of the fuel spacer 27 and the channel box 7 not shown. Since the coolant passing through the coolant passage is also directed to the nearest fuel rod 2, the flow rate of the coolant is smaller than that in the central portion, so that the fuel rods 2 arranged in the outer peripheral portion having a low thermal margin. Also, regarding the above, the effect of improving the effective marginal output of fuel can be obtained.

As shown in the schematic longitudinal sectional view of FIG.
The spring 37 for supporting the fuel rod 2 in the fuel rod insertion portion 30 of the fuel spacer 27 has its root integrally connected to the member on the upstream side of the coolant flow path, and its tip portion presses the surface of the fuel rod 2 into pressure contact. ing. Therefore, the droplet 25 in the vapor as the coolant flowing in the direction of the white arrow 8 through the fuel rod insertion portion 30 which is a part of the coolant passage adheres to the spring 37 and becomes the liquid film 21.
Since the fuel is guided to the fuel rod 2 along the surface of the fuel rod 37, the flow rate of the liquid film 21 formed on the surface of the fuel rod 2 increases and the limit output of fuel improves.

Fuel spacer 27 in the first embodiment
Is a plurality of cells 28 and a supporting band formed by bending an integrated plate member and then welding the free ends.
Assemble 29 as shown in Fig. 1 and align them with each other.
Since the 33 and the alignment recess 34 are fitted together and the abutting protrusions 32, 40 are welded to each other, the manufacturing is easy with a small number of parts, and it is robust and is not easily damaged, resulting in high reliability. high.

The second embodiment relates to claims 8 to 9, wherein the main body portion of the cylindrical ferrule cell 44 as shown in the perspective view of FIG. 5A is the perspective view of FIG. 5B. It has the same shape as the metal cell 12 in the conventional round cell type fuel spacer 13 shown in, but has a configuration in which an arc-shaped extension portion 45 is integrally provided with a member at a part of the downstream side so as to project. In addition, the fuel rod 2 that is inserted inside has a small protrusion, as in the case of the conventional metal cell 12.
It is supported by a spring restraining body 19 (not shown) provided in 18 and the connection window 46.

Further, the ferrule cell 44 is shown in FIG.
As shown in the perspective view of the main part of (a), it is arranged at the outermost periphery of the ferrule cell without the extension parts 45 arranged in the central part and inside the support band 48 provided with the integral flow tab 47 at the downstream end. A fuel spacer 49 is formed (claim 8). The extension portion 45 of the ferrule cell 44 is projected to the downstream side from the downstream end of the ferrule cell without the extension portions 45 arranged in plural in the central portion (claim 9).

Next, the operation of the above configuration will be described. In the fuel spacer 49, the liquid film 21 of the coolant flowing in the flow path surrounded by the fuel rod 2 and the support band 48 is formed by the support band as shown by the arrow as shown in the horizontal cross-sectional view of the main part of FIG.
At the downstream end of 48, the flow tab 47 guides the fuel rod 2 to the extension 45 of the ferrule cell 44. As a result, as shown in the horizontal cross-sectional view of the main part of FIG. 6C, even in the fuel rods 2 arranged at the outermost periphery of the fuel assembly, the surface liquid film
Since the flow rate of 21 is sufficiently secured, the limit output of fuel is improved.

The third embodiment is a modification of the second embodiment according to claim 10, and the front view of the main part of FIG. 7 is a fuel spacer 49.
Extension 45 of ferrule cell 44 and support band 48 in
3 shows the positional relationship with the flow tab 47 of FIG. Figure 7
Since the flow tab 47c integrally provided at the downstream end of the support band 48 shown in (c) is a conventional type and has a linear cross section,
The flow of the liquid phase is guided to the downstream side of the fuel rod 2 and the extension portion 45 of the ferrule cell 44 at the outermost periphery of the fuel assembly, as shown by the arrow 50c, and the thermal flow of the fuel rods 2 arranged at the outermost periphery is performed. It contributes to improving the margin.

However, the flow tab 47a of the support band 48 shown in FIG. 7A has a curved cross section and is integrally provided at the downstream end of the support band 48. Further, the flow tab 47b of the support band 48 shown in FIG. 7 (b) is formed integrally with the downstream end of the support band 48 so that its cross section is bent (claim 10).

As a function of the above structure, the liquid film of the coolant flowing in the flow path surrounded by the fuel rod 2 and the supporting band 48 in the fuel spacer 49 is indicated by the arrow 50a by the flow tab 47a at the downstream end of the supporting band 48. The flow tab 47b is bent into a curved shape as shown by an arrow 50b.

As a result, the liquid film of the coolant is formed on the flow tab 47 shown in FIG. 7C at the downstream end of the support band 48.
As compared with the case of c, since it is guided to the upstream side of the extension portion 45 of the fuel rod 2 and the ferrule cell 44, it is easily captured by the extension portion 45 of the fuel rod 2 and the ferrule cell 44, so that the liquid phase is captured. As the amount of fuel increases, a thick liquid film is formed on the surface of the fuel rods 2 to secure a sufficient flow rate, which further increases the thermal margin of the fuel arranged on the outermost periphery, contributing to the improvement of the fuel's limit output. To do.

The ferrule cell 51 provided with the extension 45 shown in the perspective view of FIG. 8 is another modification of the second embodiment.
In the extension 45 provided at the downstream end of the ferrule cell 51,
The outside of the tip 45a is formed by inclining the inside at an acute angle.

The operation of the above construction is that the liquid film flowing along the outer periphery of the ferrule cell 51 is the tip 45 of the extension portion 45.
Since the liquid film flowing inward in the direction of arrow a is also efficiently guided to the surface of the fuel rod 2 (not shown) inserted in the ferrule cell 51, the liquid film flowing inward is also efficiently obtained.

The fourth embodiment relates to claim 11, and relates to a lower tie plate of the fuel assembly. As shown in the vertical sectional view of FIG. 9, a fuel assembly 53 has a plurality of fuel rods 2 arranged in a channel box 7 fixed by an upper tie plate 5 and a lower tie plate 54 and arranged in the axial direction. The fuel spacers 3 maintain the mutual distance between the fuel rods 2 and the like.

Regarding the lower tie plate 54, FIG.
As shown in the plan view of (a) and the vertical cross-sectional view of FIG. 10 (b), at the downstream end of the outermost periphery, a coolant 55 inclined inward with respect to the flow direction of the coolant represented by the white arrow 8 is shown. A plurality of plate-like projections 56, which are a flow rate redistribution mechanism, are provided and configured.

As shown in the enlarged perspective view of the main part of FIG. 11, the projection 56 is located at the outermost periphery of the lower tie plate 54 from the downstream end to a vertical line 57 (here, the direction of the flow of the coolant indicated by the white arrow 8). The same as the above) and an inclination of 55 at an arbitrary angle, and a circumferential length 58 in the flow direction is the lower tie plate.
It changes monotonically along the downstream end of 54, and changes in the circumference 58 are the same between adjacent protrusions 56 (claim 1
1).

Next, the operation of the above configuration will be described. The coolant that enters from the lower tie plate 54 and flows in the fuel assembly 53 has a plurality of plate-shaped projections 56 that are a flow rate redistribution mechanism of the coolant at the downstream end around the lower tie plate 54.
Can change the direction. Ie lower tie plate
As shown in the schematic plan view of FIG. 12 (a), a swirl flow 59 in the direction of the arrow is induced by the projections 56 on the entire downstream surface of 54, and the centrifugal force causes the outer peripheral flow rate in the vicinity of the inner wall of the channel box 7. As it increases, mixing of the coolant is promoted.

The plurality of plate-like projections 56 are separated from the flow on the upper surface of the projections 56 or in the immediately downstream portion with respect to the coolant flow rate of about 2 m / s which is the normal operating condition of a boiling water reactor. In consideration of suppressing the occurrence of turbulence, it is desirable that the angle be about 20 degrees or less. Further, the maximum value of the circumferential length 58 needs to be equal to or less than the length projected on the cross section perpendicular to the flow so that the interference with the fuel rod 2 does not occur.

A ₀ -A ₁ of FIG. 10 (a) shown in FIG. 12 (b).
Flow rate distribution characteristic diagram in cross section and diagram shown in Fig. 12 (c)
As shown in the flow rate distribution characteristic diagram in the B ₀ -B ₁ cross section of 10 (a), in the case of the conventional lower tie plate 6 shown by the dotted lines 60 and 61, the flow rate decreases near the outer circumference. However, in comparison with this, in the lower tie plate 54 of the fourth embodiment, as shown by the solid lines 62 and 63, the flow rate of the outer peripheral portion increases and the flow rate distribution of the coolant in the flow passage cross section becomes flat.

For the flattening of this flow rate distribution, the swirling flow is used.
Since the mixing of the coolant in the cross section of the flow channel is promoted by 59 and the temperature of the coolant is lowered, FIG. 12 (b) shown in FIG.
At the outer peripheral position C in, the boiling point of the coolant moves to the downstream side as shown by the solid line 65, as compared with the conventional dotted line 64. Further, at the position D near the center in FIG.
As shown in FIG. 13B, the solid line 67 is different from the conventional dotted line 66.
It is easily performed because it moves to the upstream side as shown by.

In general, regarding the behavior of the coolant in the axial direction of the fuel assembly 53 shown in FIG. 9, as shown in the distribution characteristic diagram of the void fraction and the liquid temperature in FIG.
68 to subcooled boiling 69 (a, b), then saturated boiling 70
And the annular spray flow 71.

Since the surface temperature of the fuel rod 2 is higher in the sub-cooled boiling region 69 than in the saturated boiling region 70,
The cladding tube forming the surface of the fuel rod 2 has a high corrosiveness due to the influence of temperature, and has a characteristic that the corrosiveness is relatively large. Further, the voids on the surface of the fuel rod 2 are not preferable because they easily disappear due to the disturbance of the coolant or the like, which leads to output fluctuation.

However, in the fourth embodiment, as shown in FIG.
Bottom position of the effective heat generating portion 72 in the fuel assembly 53 shown in FIG.
In 73, since the coolant temperature decreases due to the increase in the flow rate due to the swirling flow 59, there is an effect of shortening the length of the thermally non-equilibrium subcool boiling region in which voids exist only near the surface of the fuel rod 2. Therefore, the life of the fuel rod 2 can be reduced and the output fluctuation can be reduced.

The fifth embodiment relates to claim 12 and is a modification of the fourth embodiment, wherein an enlarged perspective view of an essential part of FIG. 15A is provided at the downstream end of the outermost periphery of the lower tie plate 54. And Fig. 15
As shown in the enlarged plan view of the main part of (b) and the enlarged side view of the main part of FIG. 15 (c), the inside of the coolant flow direction (vertical line 57) shown by the white arrow 8 A plurality of plate-shaped projections 74 inclined 55 are provided as a coolant flow rate redistribution mechanism.

The plate-shaped protrusion 74 is formed on the lower tie plate 54.
The base line 77 is located at an angle 76 from the horizontal line 75 at the downstream end on the outermost periphery of the base line 77, and is inclined inward at an inclination 55 of an arbitrary angle with respect to the vertical line 57. The changes in 58 and the like are similar to those in the fourth embodiment.

The operation of the above configuration is that the shape of the protrusion 74 is inclined at the base line 77 having an angle 76 with the horizontal line 75, so that the coolant inside the fuel assembly 53 is provided downstream of the lower tie plate 54. The influence of the forced flow 78 in the direction shown by the arrow in FIG.

As a result, a swirl flow 59 can be generated in the vicinity of the inner wall of the channel box 7 in the cross section perpendicular to the flow of the coolant on the entire downstream surface of the lower tie plate 54, and the inclination 55 and the angle 76 An optional compulsory flow 78 is obtained by selection. Therefore, an arbitrary swirl flow 59 can be generated more easily than in the fourth embodiment. The other actions and effects are similar to those of the fourth embodiment.

The sixth embodiment relates to claims 13 to 15, and relates to a fuel spacer and a fuel assembly. Figure 16 (a)
As shown in the schematic front view of FIG. 9, in the fuel assembly 53, a plurality of fuel spacers 3 are provided in the axial direction.
In the vicinity of the lowermost end position 73 of the effective heat generating portion 72 shown in FIG. 7, a fuel spacer 79 provided with a plate-like projection 56 which is a coolant flow rate redistribution mechanism is arranged (claims 15 and 16).

The fuel spacer 79 provided with the plate-like protrusion 56 is provided at the downstream end of the support band 80 as shown in the schematic plan view of FIG. 16 (b) and the schematic side view of FIG. 16 (c). The lower tie plate 54 shown in FIGS. 10, 11 and 15 in the fourth and fifth embodiments integrally with the member on the outer periphery
The projection 56 or the projection 74, which is similar to that provided in the above, is provided (claims 13 and 14).

Next, the operation of the above configuration will be described. A plurality of fuel spacers 3 of the fuel assembly 1 in the boiling water reactor are installed in the axial direction within the fuel assembly 1, and the gaps between the fuel rods 2 and the water rods 16 and the channel box 7 are provided. The gap between the fuel rod 2 and the fuel rod 2 is maintained at a predetermined value, and the coolant passage in the fuel assembly 1 is secured to maintain the function of the fuel assembly 1.

Therefore, the points generally taken into consideration in the design of the fuel spacer 3 are as follows (1) seismic resistance of the fuel assembly 1, (2) maintaining the distance between the fuel rods 2, and (3) fuel. Vibration suppression in rod 2, (4) allowance for thermal expansion of fuel rod 2,
(5) Easy assembly of the fuel assembly 1, (6) Minimization of contact area with the fuel rod 2, (7) Maximization of thermal limit output,
(8) Minimize pressure loss of the fuel assembly 1, (9) Minimize parasitic neutron absorption, and (10) Minimize the number of parts.

Among these, regarding the axial arrangement of the fuel spacer 3, the maximum spacing may be limited by (1) to (3), but the fuel spacer 79 according to the sixth embodiment is not limited.
By combining this fuel spacer 79 in the axial direction, (7) thermal limit output and (8) improvement of pressure loss performance,
Also, the nuclear performance can be improved by reducing the void ratio.

In the normal operating state of the boiling water reactor, FIG.
The flow in the vicinity of the lowermost position 73 of the effective heat generating portion 72 shown in FIG.
As shown in, the liquid single-phase flow 68 or the flow with a low void ratio is obtained, and the coolant temperature is relatively nonuniform.

Therefore, particularly by disposing the fuel spacer 79 having the projections 56 and 74 for the function of redistributing the flow rate of the coolant at this position, the fourth embodiment described above is performed in the vicinity of the lowermost end position 73 of the effective heat generating portion 72. In the same manner as in the first embodiment and the fifth embodiment, since the flow rate is increased by the swirling flow 59 of the coolant, the fuel rod 2
This has the effect of shortening the length of the thermally non-equilibrium subcooled boiling region in which voids exist only near the surface of the fuel rod 2. Therefore, the longevity of the fuel rod 2 and the output fluctuation can be reduced.

The seventh embodiment relates to claims 1 to 16, and relates to a fuel assembly in which the fuel spacer and the lower tie plate of each of the above-mentioned embodiments are used alone or in combination. As a boiling water type fuel assembly, a plurality of fuel rods and water rods are arranged between the upper tie plate and the lower tie plate, and a plurality of fuel spacers are arranged in the axial direction, and in the rectangular tubular channel box. It is formed by inserting into.

At this time, the fuel spacers 31 and 4 in the first to third embodiments and the sixth embodiment described above are used.
The lower tie plate 54 in each of the ninth and 79th embodiments, the fourth and fifth embodiments, and the fuel assembly 53 in the sixth embodiment are configured individually or in combination of a plurality of types.

The operation of the above structure is as follows. In the fuel assembly, the effect of reducing the flow resistance of the coolant obtained by the fuel spacers 31, 49, 79 and the lower tie plate 54 is reduced, and the capacity of the coolant circulating pump is reduced. The operating efficiency of the furnace can be improved and the limit output of fuel can be improved.

Particularly, by directing the coolant to the fuel rods 2 arranged on the outermost periphery, the thermal margin of the fuel rods 2 on the outermost periphery can be increased. Further, the flow rate redistribution function of the coolant makes the flow rate of the coolant flat and makes the temperature uniform, so that the limit output of fuel and the soundness of the fuel rod 2 are improved.

[0108]

As described above, according to the present invention, in the fuel assembly of the boiling water reactor, the flow resistance of the coolant in the fuel spacer is reduced to reduce the capacity of the coolant circulation system facility and improve the design flexibility. As a result, the operating efficiency of the nuclear power plant is improved. Further, the fuel spacer and the lower tie plate improve the margin of the thermal output in the fuel rods arranged at the outermost periphery, and the limit output of the fuel and the soundness of the fuel rods are improved from the redistribution of the flow rate of the coolant. Since the structure of each part of the fuel spacer is simplified, it is robust, easy to manufacture, and highly reliable and safe.

[Brief description of drawings]

FIG. 1 is a lateral cross-sectional view of a main part of a fuel assembly according to a first embodiment of the present invention.

FIG. 2 is a perspective view of a cell constituting the fuel spacer according to the first embodiment of the present invention, in which (a) is a fuel contact portion side,
(B) The figure seen from the spring side.

FIG. 3 is a perspective view of a support band that constitutes the fuel spacer according to the first embodiment of the present invention, (a) shows no swirl vanes, and (b) shows swirl vanes.

FIG. 4 is a schematic vertical sectional view of a spring portion of the fuel spacer according to the first embodiment of the invention.

FIG. 5 is a perspective view of a ferrule cell of a fuel spacer according to a second embodiment of the present invention, in which (a) shows the present invention and (b) shows a conventional example.

FIG. 6 is a fuel spacer according to a second embodiment of the present invention, (a) is a perspective view of a main part, and (b) and (c) are transverse cross-sectional views of the main part showing the behavior of a liquid film.

FIG. 7 is a front view of a main part of a fuel spacer according to a third embodiment of the present invention, in which (a) shows a curved flow tab, (b) shows a bent flow tab, and (c) shows a linear flow tab.

FIG. 8 is a perspective view of a modified ferrule cell of the fuel spacer according to the third embodiment of the present invention.

FIG. 9 is a partially cutaway front view of a fuel assembly according to a fourth embodiment of the present invention.

FIG. 10 is a lower tie plate of a fourth embodiment according to the present invention, (a) is a plan view and (b) is a longitudinal sectional view.

FIG. 11 is an enlarged perspective view of a main part of a protrusion according to a fourth embodiment of the present invention.

FIG. 12 is a lower tie plate according to a fourth embodiment of the present invention, (a) is a schematic plan view, (b) is a flow distribution characteristic diagram of the A ₀ -A ₁ cross section in FIG. 10 (a), c) is shown in Figure 10.
Flow distribution characteristic diagram of B ₀ -B ₁ section in (a).

FIG. 13 is an axial void fraction distribution characteristic diagram in the fourth embodiment according to the present invention, where (a) is the C position on the outer periphery in FIG. 12 (b), and (b) is the center position in FIG. 12 (b). Of D
Indicates the position.

FIG. 14 is a behavior characteristic diagram of the coolant along the axial direction of the fuel rods in the fuel assembly.

FIG. 15 is an enlarged view of a main part of a protrusion according to a fifth embodiment of the present invention, in which (a) is a perspective view, (b) is a plan view, and (c) is a side view.

FIG. 16 is a fuel assembly of a sixth embodiment according to the present invention, (a) is a schematic front view showing the arrangement of fuel spacers in the fuel assembly, (b) is a schematic plan view of the fuel spacer,
(C) is a schematic side view of the fuel spacer.

FIG. 17 is a partially cutaway front view of a conventional fuel assembly.

FIG. 18 is a plan view of (a) and a partially cutaway side view of a conventional lattice type fuel spacer.

FIG. 19 is a plan view of a conventional round cell type fuel spacer.

FIG. 20 is a diagram of an iso-steam flow velocity in a conventional fuel assembly.

FIG. 21 is a schematic diagram of a coolant behavior between conventional fuel rods.

[Explanation of symbols]

1, 31, 53 ... Fuel assembly, 2 ... Fuel rod, 3, 27, 49, 79
... Fuel spacer, 4 ... Handle, 5 ... Upper tie plate, 6, 54 ... Lower tie plate, 7 ... Channel box, 8 ... Coolant flow direction (white arrow), 9 ... Strip plate, 1
0, 29, 48, 80 ... Support band, 11 ... Lattice type fuel spacer, 12 ... Metal cell, 13 ... Round cell type fuel spacer, 14 ...
Lantern type spring, 15 ... Supporting member, 16 ... Water rod, 17 ... Outer projection, 18 ... Small projection, 19 ... Spring restraining body, 20 ... Large water rod, 21 ... Liquid film, 22 ... Low flow rate part, 23 ... High Flow velocity part, 24 ... Torsion plate, 25 ... Droplet, 26 ... Swirl flow, 28 ... Cell, 30 ... Fuel rod insertion part, 32, 40 ... Projection part, 33
... Aligning convex portion, 34 ... Aligning concave portion, 35, 43 ... Intermediate portion, 36 ... Fuel contact portion, 37 ... Spring, 38 ... Welding, 39 ... Swivel blade, 41 ... Bathtub, 42 ... Flow tab, 44, 51 ... ferrule cell, 45 ... extension, 45a ... tip of extension, 46 ... connecting window, 47, 47a-47c ... flow tab, 50a-50c ... arrow,
52 ... Liquid film flow direction (arrow) 55 ... Inclination, 56, 74 ... Protrusion,
57 ... Vertical line, 58 ... Perimeter, 59 ... Swirl flow, 60, 61, 64, 66 ...
Dotted line, 62, 63, 65, 67 ... Solid line, 68 ... Liquid single-phase flow, 69 ... Subcool boiling, 70 ... Saturated boiling, 71 ... Annular spray flow, 72 ... Effective heat generating part, 73 ... Effective heat generating part bottom end position , 75 ... horizon, 76
… Angle, 77… Baseline, 78… Forced flow.

Claims (16)

[Claims] 1. A fuel spacer in which a plurality of cells, each of which independently forms a fuel rod insertion portion for inserting a plurality of fuel rods and a water rod at substantially equal intervals, are arranged in a substantially lattice pattern, and which has four centers. The fuel rod insertion portion is formed between the plurality of cells aligned with the center of the flow path between the fuel rods and the support band arranged on the outer periphery of the plurality of cells, and cooling is provided at the downstream end of the cell. A fuel spacer characterized in that a swirl vane for guiding a material is integrally provided with a flow tab at a downstream end of the support band. 2. The fuel spacer according to claim 1, wherein a swirl vane that guides a coolant is integrally provided at a downstream end of a support band that forms a fuel spacer together with the cells. 3. A fuel contact portion for supporting a fuel rod and a spring are integrally provided with the cell and the support band in a fuel rod insertion portion formed between the cell and the support band. The fuel spacer according to claim 1 or claim 3. 4. The fuel spacer according to claim 1, wherein the cell and the support band are each cut out from a member, and the ends are fixed after bending. 5. The positioning protrusions or the positioning recesses to be assembled with each other are provided on the protrusions that abut the adjacent cells and support bands in the cells and the support bands. Fuel spacer. 6. The fuel contact portion for supporting the fuel rod in the fuel rod insertion portion has a free end fixed to the cell after being cut and bent from the member of the cell and the support band. The fuel spacer according to claim 1. 7. A spring for supporting a fuel rod in the fuel rod insertion portion is cut out from the member of the cell and the support band and bent, and the side integrated with the member is made the upstream side of the coolant passage. The fuel spacer according to any one of claims 1 to 5. 8. A ferrule that is arranged at the outermost periphery in a fuel spacer in which ferrule cells that individually insert a plurality of fuel rods and water rods are arranged in a grid pattern at substantially equal intervals and a supporting band is arranged at the outer periphery. A fuel spacer, wherein an extension portion is provided inside the fuel assembly at a downstream end of the cell, and a plurality of flow tabs are provided at a downstream end of the support band. 9. The extension part provided inside the fuel assembly at the downstream end of the ferrule cell is made to project downstream from the ferrule cell located at the center of the fuel assembly. Fuel spacer. 10. The fuel spacer according to claim 8, wherein the flow tab provided at the downstream end of the support band is inclined inside the fuel assembly in a curved or bent cross section. 11. In a lower tie plate of a fuel assembly, which fixes a lower portion of a plurality of fuel rods and water rods arranged in a grid pattern at substantially equal intervals, a flow of a coolant at a downstream end at an outermost periphery of the lower tie plate. A plurality of plate-shaped projections inclined with respect to the direction are provided, and the circumferential length of the projections projected in the vertical direction monotonously changes along the downstream end, and the change in the circumferential length is the same between adjacent projections in the same direction. Lower tie plate characterized by being. 12. The lower tie plate according to claim 11, wherein a plurality of protrusions provided at the outermost periphery of the lower tie plate at the downstream end incline a base line of inclination with respect to the flow of the coolant from a horizontal line. 13. A fuel spacer for supporting a plurality of fuel rods and water rods, the upper and lower parts of which are fixed by an upper tie plate and a lower tie plate, in a grid pattern at substantially equal intervals,
A plurality of plate-shaped projections that are inclined with respect to the flow direction of the coolant are provided at the downstream end at the outermost periphery of the fuel spacer, and the circumferential length of the projections projected in the vertical direction changes monotonically along the downstream end. The fuel spacer is characterized in that the change in the circumferential length is the same between adjacent protrusions. 14. The fuel spacer according to claim 13, wherein a plurality of projections provided at the outermost periphery of the fuel spacer at the downstream end incline a base line of inclination with respect to the flow of the coolant from a horizontal line. 15. A plurality of protrusions, which are inclined with respect to the flow direction of the coolant, are provided at the downstream end at the outermost periphery, and the perimeters of the protrusions projected in the vertical direction monotonously change along the downstream end and are adjacent to each other. 15. The fuel assembly according to claim 13 or 14, wherein the fuel spacers having the same circumferential length change between the protrusions are arranged near the lowermost end of the effective heat generating portion of the fuel assembly. 16. A fuel assembly in which a plurality of fuel rods and water rods are arranged between an upper tie plate and a lower tie plate to arrange a plurality of fuel spacers in an axial direction and are inserted into a rectangular tubular channel box. Forming a fuel rod insertion portion between a plurality of cells whose center coincides with the center of the flow path between the fuel rods and a supporting band arranged on the outer periphery thereof, and at the downstream end of the cell, a swirl vane and a supporting band. A fuel spacer integrally provided with a flow tab at the downstream end of
A ferrule cell that is arranged in a lattice at approximately equal intervals and that allows a plurality of fuel rods and water rods to be inserted independently and is arranged at the outermost periphery is provided with an extension portion inside the fuel assembly at the downstream end and at the outer periphery. A fuel spacer provided with a plurality of flow tabs at the downstream end of the supporting band, and a plurality of plate-shaped projections provided at the downstream end of the outermost circumference, and the circumferential length of the projection projected in the vertical direction monotonically along the downstream end. 16. The lower tie plate, the fuel spacer, and the like, which are changed and have the same circumferential length change between adjacent protrusions, are provided singly or in a proper combination of a plurality of types. Fuel assembly.