JPH06230163A - Fuel spacer and fuel assembly - Google Patents

Abstract

PURPOSE:To provide a fuel spacer and a fuel assembly in which the limit output is enhanced through a simple constitution by adhering a coolant, with low pressure drop, to the surface of a fuel rod by means of a swirl vane provided on the ferrule of the fuel spacer. CONSTITUTION:In fuel spacers 19b, 19c for coupling a plurality of tubular ferrules passing a plurality of fuel rods 5, 9 and holding the fuel rods 5, 9 laterally at predetermined positions, a swirl vane is formed extending obliquely upward with the end part thereof extending outward of the tubular ferrule from the upper end of the side wall thereof (downstream side of coolant) and the swirl vane is protruded farther downstream side than the downstream side end of the side wall of the tubular ferrule. The fuel spacers 19b, 19c arranged with vanes twisted normally to the flowing direction of the coolant are disposed appropriately on the downstream side of the upper end of the side wall of the tubular ferrule in a coiling material channel formed by the adjoining side walls of the coupled tubular ferrules.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel assembly for a nuclear reactor, and more particularly to a fuel spacer for holding the fuel assembly and fuel rods.
And a tubular ferrule for inserting a fuel rod.

[0002]

2. Description of the Related Art Conventionally, a structure shown in FIG. 2A of JP-A-59-65287 has been proposed as a fuel spacer for a fuel assembly used in a boiling water reactor. This fuel spacer is configured by arranging a large number of tubular ferrules into which fuel rods are inserted in a lattice shape, and adjoining adjacent tubular ferrules by welding. A water rod, like the fuel rod, is also inserted in this tubular ferrule.

A conventional fuel spacer and a fuel assembly using this fuel spacer will be described with reference to FIGS. 41 to 47. FIG. 41 is an example of a fuel assembly used in a boiling water reactor, and shows a partially cut front view. The fuel assembly 1 includes an upper tie plate 3 having a handle 2, a lower tie plate 4, a number of fuel rods 5 supported at both ends by an upper tie plate 3 and a lower tie plate 4, and the fuel rods 5.
And a fuel spacer 7a, 7b arranged in the axial direction.

In general, the fuel spacers 7a and 7b are 5 at the bottom.
This fuel spacer 7
The distances in the horizontal direction between the plurality of fuel rods 5 and the water rods 6 are kept constant by a and 7b. further,
The square tube-shaped channel box 8 is used for the fuel spacer 7.
It surrounds a bundle of fuel rods 5 and water rods 6 bundled by a and 7b. The channel box 8 is attached to the upper tie plate 3.

A part of the fuel rod is a short fuel rod 9, and only the lower end of the fuel rod is held by the lower tie plate 4. A cooling water inlet 6a is provided at the lower end of the water rod 6, and a cooling water outlet 6b is provided at the upper end.

The fuel spacer 7a is a plan view of FIG. 42 and is a view taken along the line AA of FIG. 41, and the fuel spacer 7b is a plan view of FIG.
As shown in a BB arrow view of 41, the same number of tubular ferrules 10 as the fuel rods 5 and the short length fuel rods 9 are arranged in a lattice,
The outer periphery of the bundle of tubular ferrules 10 is a band-shaped support band 11
Surrounded by. A plurality of upwardly protruding (projecting to the downstream side) 11a that are curved inward are provided between the fuel rods 5 at the upper end of the support band 11. Furthermore, the tubular ferrules 10 arranged in a lattice are joined to the adjacent tubular ferrules 10 by spot welding.

As shown in the perspective view of FIG. 44, a tubular ferrule
No. 7 of Japanese Examined Patent Publication No. 63-48031 at both ends of 10 or in the vicinity
Two protrusions as shown in the figure or two protrusions as shown in FIGS. 3A and 3B of JP-A-59-65287 are provided respectively. These protrusions 10a are formed by projecting a part of the ferrule 10 inward. The adjacent tubular ferrules 10 are spot-welded 12 at the upper and lower ends.

Two adjacent tubular ferrules 10
The continuous loop spring 13 shown in FIG. 42 and FIG. The shape of this continuous loop spring 13 is disclosed in
-65287, which is the same as that disclosed in FIG. 4 of the publication, in which the central portion in the height direction projects outward.

The portion to which the continuous loop spring is attached is disclosed in Japanese Patent Laid-Open No. 62-287184, FIG. 1 and FIG. 2, and a rectangular shape is formed in a longitudinal direction at one location on the side cylindrical portion of the tubular ferrule 10 shown in FIG. The notch 14 is provided, and this notch
One end of 14 or in the vicinity of the upper and lower ends (upper and lower parts of the notch 14 in FIG. 44) has a shape in which the claws 15 project, and the same notches 14 of adjacent tubular ferrules 10 are butted against each other.
These claws 15 hold the continuous loop spring 13 for pressing the fuel rod. As a result, the tubular ferrules 10 are assembled in a lattice shape.

In recent years, a fuel spacer in which the water rod 6 has a diameter larger than the inner diameter of the tubular ferrule 10 has been developed, and an example of such a fuel spacer is disclosed in JP-A-61-198096.
The one shown in FIG. 1 of the publication is proposed. Further, the fuel spacers 7a and 7b in which the conventional tubular ferrules 10 are arranged in a lattice form facilitate the insertion of the fuel rods 5, and
A chamfer is formed on the inside of the end face so that the upper and lower ends of the tubular ferrules 10 adjacent to each other can be easily spot-welded 12.

An enlarged perspective view of an essential part of FIG. 45 and an enlarged sectional view of an essential part of FIG. 46 show an example of a fuel assembly used in a boiling water reactor, that is, a plurality of fuel rods 5 in a square channel box 8. The main part of a fuel assembly arranged in a square lattice as a whole is shown.

In the boiling water type light water reactor, the heat generated by the nuclear fission of the uranium fuel loaded in the fuel rods 5 is removed by cooling water which is a coolant flowing from the lower part of the fuel assembly,
On the other hand, a part of the cooling water heated by the fuel rods 5 becomes vapor in the fuel assembly and is extracted to the outside to rotate the turbine.

The cooling water flowing through the inside of the channel box 8 flows in as a liquid phase flow from the lower portion of the fuel assembly, and is heated by the fuel rods 5 while it rises inside the channel box 8 to boil. Becomes a two-phase flow and passes to the upper part.

In the upper part of the fuel assembly, the gas phase is mainly
Although flowing in a relatively wide flow path between the fuel rods 5, a part of the liquid phase accompanies the gas phase to form droplets, and part of the liquid phase flows on the surface of the fuel rods 5 and the inner surface of the channel box 8. Flows in a film. When the liquid film flowing on the fuel rod surface decreases,
The heat transfer coefficient on the surface of the fuel rod may decrease (boiling transition start) and overheating may occur.

[0015]

In recent years, the mechanism of the relationship between the occurrence of boiling transition of the fuel assembly 1 and the shape of the fuel spacers 7a and 7b has been elucidated, and when the output of the fuel assembly 1 approaches the limit output, the axial direction is increased. 2 to 1 from the top of the fuel spacers 7a and 7b arranged in plural (currently 7 to 8).
It is known that boiling transition is likely to occur near the lower end side (upstream side) of the stage. In addition, the circumferential position of the fuel rod surface where the boiling transition is occurring is the center of the fuel rod flow passage 17 surrounded by four fuel rods 5 as shown in the flow velocity distribution diagram of the fuel rod flow passage in FIG. It is known that it is the portion facing (the fuel rod surface portion 16 in the direction of 45 degrees in FIG. 47).

The fuel spacers 7a and 7b act to stir the two-phase flow to adhere droplets of the coolant to the surface of the fuel rod downstream of the fuel spacer to thicken the liquid film.
On the upstream side of the fuel spacer, the liquid film flowing along the surface of the fuel rod is thinned as a result of the turbulence of the flow of the two-phase flow, and the boiling transition is likely to occur.

Incidentally, FIG. 47 shows the flow velocity distribution of the two-phase flow in the fuel rod passage 17 surrounded by four fuel rods by contour lines.
The smaller the number shown with a subscript on this contour line, the higher the flow velocity. As a result, the flow velocity distribution is 0 on the fuel rod surface.
It can be seen that the 90 degree part is slow and the 45 degree part is fast. The measurement result of the liquid film thickness on the fuel rod surface near the lower end of the fuel spacer where the boiling transition is likely to occur by the experiment also shows that the liquid film tends to be thin at the fuel rod surface portion 16 in the 45 ° direction.

Since the flow velocity at the 0 ° and 90 ° portions is relatively low, the liquid film is thick. On the other hand, at the 45 degree portion (diagonal direction), the flow path is wide, so the flow velocity is high, and the liquid film becomes thin. It is considered that this result is the fuel rod surface portion 16 in the diagonal direction (45 degrees) near the lower end of the fuel spacer when the conventional boiling transition occurs.

Immediately after the passage of the fuel spacers 7a, 7b, the flow separates at the downstream end of the tubular ferrule of the fuel spacers 7a, 7b to generate a turbulent flow near the fuel rods. Since the droplets adhere to the surface of the fuel rod due to the turbulence of the flow, the liquid film flow rate becomes larger than that before the passage of the fuel spacers 7a and 7b. This is the effect of improving the limit output by the fuel spacers 7a and 7b.

Particularly in the tubular ferrule, since the droplets in the two-phase flow adhere to the side wall of the tubular ferrule 10 and are scattered again in the two-phase flow at a position near the fuel rod surface at the downstream end, the droplets on the fuel rod surface are The sticking probability increases, contributing to an increase in the liquid film flow rate on the surface of the fuel rod. From these, it is conceivable to efficiently capture the droplets in the two-phase flow and change the flow of the two-phase flow so as to easily adhere to the fuel rod surface.

As this method, JP-A-2-285286, No. 2, 4, 5, 6, 8 of "Fuel assembly and fuel spacer"
As shown in the figure, a part of the side wall of the tubular ferrule is bent outward to form a swirl vane, or a swirl vane
A structure is disclosed for insertion into a channel surrounded by the outer surface of the side walls of two tubular ferrules.

However, in this example, the flow of the two-phase flow due to the swirling vanes only causes the droplets contained in the two-phase flow to adhere to the side wall of the tubular ferrule or the circular tube of FIG. 6, and as a result. When the droplets are scattered to the downstream side, only the droplets are scattered from the fuel spacer member near the surface of the fuel rod. This only slightly strengthens the aspect on the downstream side in the basic flow of the tubular ferrule, and the degree of improvement in the limit output is small relative to the increase in fuel spacer pressure loss.

In addition, a fuel spacer is constituted by swirl vanes as a device for directing a swirling flow in a flow path to a droplet flowing along with vapor to a fuel rod (JP-A-1-132990). However, such a fuel spacer has problems in the spacer strength and the fuel rod supporting method.

Although it is considered that the number of the fuel spacers 7a and 7b attached to the fuel assembly 1 is increased to improve the limit output, when the number of the fuel spacers 7a and 7b is increased, the cross section of the flow passage is sharply reduced and sharply reduced. A relatively large local pressure loss due to expansion (a relatively large portion of the axial pressure loss of the fuel assembly 1 is occupied by the local pressure loss of the plurality of fuel spacers 7a, 7b). However, the stability will be disadvantageous.

Further, the required pump head for circulating the coolant in the core increases, which is economically disadvantageous. Also, in order to increase the cooling efficiency by increasing the ratio of the coolant used for cooling the fuel rods on the outer periphery of the fuel bundle, the liquid film flowing on the inner surface of the channel box that does not contribute to the cooling of the fuel rods As having the effect of turning around,
It has been proposed to provide a groove for separating the liquid film flow on the inner surface of the channel box. However, the effect on the inside of the second layer of the fuel bundle is small.

However, in the conventional fuel spacers 7a and 7b using the tubular ferrule 10 as shown in FIGS. 45 and 46, the effect of directing the droplets accompanying the vapor to the fuel rod 5 is small.

The object of the present invention is to attach a coolant to the surface of the fuel rod with a small increase in pressure loss by means of swirl vanes or the like provided on the ferrule of the fuel spacer, and to make the fuel structure simple and to improve the limit output. Providing a spacer and a fuel assembly.

[0028]

According to the present invention, there is provided a fuel spacer for holding a fuel rod laterally at a predetermined position by connecting tubular ferrules each of which penetrates a plurality of fuel rods including a water rod. The end of the side wall of the tubular ferrule (downstream of the coolant) is extended outward of the tubular ferrule to form a swirl vane extending obliquely upward at the tip, and the swirl vane is further downstream from the downstream end of the side wall of the tubular ferrule. The fuel spacer is characterized in that it is projected to the side.

Further, in the coolant passage formed by the adjacent side walls of the connected tubular ferrules, the pipe is twisted in the direction perpendicular to the flow of the coolant downstream of the upper end of the side wall of the tubular ferrule (downstream of the coolant). A fuel spacer is characterized in that twisting blades are provided.

Further, in the coolant passage formed by the mutually adjacent side walls of the connected tubular ferrules, a twisted blade having a central axis at the center of the coolant passage is provided downstream of the upper end of the tubular ferrule side wall (downstream of the coolant). The fuel spacer is characterized in that it is formed so as to project from the side wall of the ferrule.

Further, in a fuel assembly in which a plurality of fuel rods, which are surrounded by a channel box and are supported by an upper tie plate and a lower tie plate, are arranged in a lateral direction by a fuel spacer arranged in a plurality of stages in a longitudinal direction, The fuel spacer connects tubular ferrules that pass through each of the fuel rods, and a tubular ferrule having an end portion from a sidewall upper end (coolant downstream side) of the tubular ferrule to a coolant passage formed by adjacent sidewalls. A fuel spacer having a swirl vane extending outwardly of the tube and extending obliquely upward at the tip, or a twisting blade twisted in the direction perpendicular to the flow of the coolant downstream of the tubular ferrule. Is a fuel assembly.

[0032]

The coolant in the fuel assembly is heated by the fuel rods and becomes a two-phase flow, which flows through the flow passage formed between the adjacent fuel rods and rises. At this time, the two-phase flow is given a swirl force by a swirl vane or a twisting blade arranged on the side wall of the tubular ferrule downstream of the fuel spacer, and this swirl force produces a large swirl flow with a small vane shape in a high flow velocity region. Occur.

Further, the droplets in the two-phase flow in the flow path far from the fuel rods are efficiently and efficiently attached to the swirling vanes or the twisted blades and scattered so as to be easily attached directly to the fuel rod surface on the downstream side of the fuel spacer. In the process, the droplets contained in the two-phase flow of the flow channel can be attached to the surface of the adjacent fuel rods by centrifugal force.

The swirl vanes or the twisted blades arranged on the side wall of the tubular ferrule can be formed by cutting a part of the side wall of the tubular ferrule and bending it. As a result, the fuel rod is easy to manufacture, the cooling efficiency of the fuel rod is improved, the boiling transition is delayed in the downstream of the fuel spacer, and the limit output is improved while suppressing the increase in pressure loss with a small number of fuel spacers.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. It should be noted that the same components as those of the above-described conventional technique are designated by the same reference numerals, and detailed description thereof will be omitted. The partially cut front view of FIG. 1 shows a fuel assembly used in a boiling water reactor. The fuel assembly 18 includes an upper tie plate 3 having a handle 2, a lower tie plate 4, a large number of fuel rods 5 supported at both ends by the upper tie plate 3 and the lower tie plate 4, and arranged between the fuel rods 5. Water rod 6 and a plurality of fuel spacers 19a, 19b, 19 arranged in the axial direction
and c.

Here, four fuel spacers 19a are provided at the bottom,
One fuel spacer 19b at the center and fuel spacer 19 at the top
An example is shown in which two c are arranged. This fuel spacer 19
With a to 19c, the fuel rods 5, the short length fuel rods 9, and the water rods 6 are held at a constant horizontal interval. Further, the channel box 8 has a fuel spacer 19
It encloses a bundle of fuel rods 5, 9 and a water rod 6 bundled by a to 19c. The channel box 8 is attached to the upper tie plate 3.

However, the short fuel rods 9 which are a part of the fuel rods may have only their lower end portions held by the lower tie plate 4. Similarly, the lower end of the water rod 6 may be held by the lower tie plate 4, and the channel box 8 may be attached to the lower tie plate 4 instead of the upper tie plate 3. A cooling water inlet 6a is provided at the lower end of the water rod 6, and a cooling water outlet 6b is provided at the upper end.

The fuel spacers 19b and 19c are shown in a partially cut front view in FIG. 2, and the fuel spacer 19a having the same shape as the conventional fuel spacer 7b is shown in a partially cut front view in FIG. In addition,
4 is a plan view of the fuel spacer 19a as seen from the direction of arrows CC in FIG. 1, FIG. 5 is a plan view of the fuel spacer 19b as seen from the direction of arrows DD of FIG. 1, and FIG. 6 is a plan view of the fuel spacer 19c. And EE in FIG.
FIG.

The fuel spacers 19a to 19c have the same number of tubular ferrules 10, 20 (21, 2) as the fuel rods 5 and the short fuel rods 9.
2 and 23) are arranged in a lattice, and the outer periphery of the bundle of tubular ferrules is surrounded by a band-shaped support band 11, and a lobe 24 projects outside the support band 11.
Of these, the fuel spacer 19a has the same specifications as those shown in FIG. 42 as a conventional example, and is a combination of tubular ferrules 10 in a lattice shape.

The fuel spacer, which is a feature of the present invention, is 19
b and 19c. Therefore, mainly the fuel spacers 19b, 19
c will be described in detail, and the difference between the fuel spacer 19a and the fuel spacer 19b will be described. The fuel spacers 19b and 19c are formed by arranging a plurality of tubular ferrules 20 shown in the perspective view of FIG.
12 are welded to each other at the contact part. This tubular ferrule
Two protrusions 20a are provided on the upper and lower ends of the 20, and these protrusions 20a are formed by projecting a part of the side wall of the tubular ferrule 20 inward.

From the vicinity of the spot weld 12 on the upper end (downstream side) of the tubular ferrule 20, the side wall end is cut open in four places in the tangential direction of the tubular ferrule 20 to form a swirl vane base member 24, and the swirl extending obliquely upward to the tip thereof. The vane 25 is provided by being bent, and the swirl vane 25 has a shape protruding further downstream from the downstream end of the side wall of the tubular ferrule 20.

As can be seen from the partially enlarged plan view of the combination of the four tubular ferrules shown in FIG. 8, the swirl vane base member 24 has four tubular ferrules adjacent to each other.
The swirl vane base members 24 projecting from 20 are formed in such a length that a slight gap is allowed so that they can be combined in a cross shape. Further, the swirl vane 25 is bent so as to deflect the flow toward the tubular ferrule with the swirl vane base member 24 supporting the swirl vane 25.

Therefore, the shape of the swirl vane 25 viewed from above, as shown in FIG. 8, substantially covers the coolant flow passage 17 on the outer side of the tubular ferrule side wall surrounded by four tubular ferrules by the four swirl vanes 25. Shaped and swirl vane
25 may extend to the inside of the tubular ferrule 20. In this case, it is necessary to secure a gap between the swirl vane 25 and the fuel rods 5, 9.

Two adjacent tubular ferrules 20
A continuous loop spring 13 is installed over the ridge, and the shape of the continuous loop spring 13 is the same as that described in JP-A-59-65287.
Some are disclosed in the figure. Basically the same shape,
The central portion in the height direction projects outward.

As shown in FIGS. 1 and 2 of Japanese Patent Laid-Open No. 62-287184, the portion to which the continuous loop spring is attached has a rectangular notch in the longitudinal direction at one location on the side cylindrical portion of the tubular ferrule. 14 is provided, and the claw portion 15 is provided in the vicinity of the upper and lower ends of the cutout portion 14 (only one end of the cutout portion 14 in the quote) so as to face the same cutout portion 14 as the adjacent tubular ferrule. Butt, and the upper and lower claws 15 hold the continuous loop spring 13 for pressing the fuel rod (see FIGS. 2 and 8). As a result, the tubular ferrule 20 is assembled in a lattice shape.

The structure of the central portion of the fuel spacers 19b and 19c is, as shown in the plan view of the main portion of FIG. 9, a hole portion formed by removing the seven tubular ferrules in the central portion, that is, the central portion. The elongated holes 26 surrounded by the side walls of the ten tubular ferrules 20 are formed.

The four bridging members 27a and 27b are shown in FIGS.
As shown in FIG. 7, the fuel spacers 19b and 19c are arranged in the hole 26 in a direction orthogonal to the diagonal line. This bridging member 27
Of the ten tubular ferrules 20 forming the hole 26 at the center of the fuel spacers 19b and 19c, the left and right ends of a are
It is attached by spot welding 12 to the side surfaces of two adjacent tubular ferrules 20 that form the ends of the elongated hole.

The bridging member 27a is composed of two upper and lower members,
The upper end or the lower end has a concave portion, and a continuous loop spring 29 is attached to this portion and welded to form a single bridging member 27a,
The left and right ends of the bridging member 27a are spot-welded 12 to the upper and lower ends of the tubular ferrule 20 at the upper and lower ends.

The bridging member 27b joins the three tubular ferrules in the abdomen of the elongated hole portion 26, while connecting the fuel spacers 19b and 19c.
A bent portion 28 protruding in a diagonal direction is formed, and the water rod 6 is supported at the corner of the bent portion 28. Further, the bridging member 27b has the same curvature as the side wall of the tubular ferrule 20, and the left and right ends and the base of the bent portion are molded. In this portion, the tubular ferrule 20 and the upper and lower ends which are adjacent to each other are spot-welded 12.

The water rod 6 is shown in FIGS.
Is inserted into the hole portion 26 as shown in FIG.
The continuous loop spring 29 provided at the position is pressed against the bent portion 28 of the bridging member 27b. Fuel spacer 19c shown in FIG.
Is a fuel spacer attached to the upper part of the fuel assembly 1 by two to four, and the tubular ferrule at the position of the short fuel rod 9 is deleted to be a space.

Of the array of tubular ferrules thus formed, the tubular ferrule around the fuel rod bundle has two swirl vanes 25 and two base members 24, as shown in FIGS.
Of the tubular ferrule 21 shown in the perspective view of FIG. 11, a tubular ferrule 22 of a swivel vane 25 in a mounting direction different from that of the tubular ferrule 21 of FIG. 10 shown in the perspective view of FIG. 11, and a swivel vane 25 of FIG. It is secured by the peripheral support band 11 using the ferrule 23. That is, the tubular ferrule 20 is arranged at the center, the tubular ferrules 23 are arranged at the four corners, and the tubular ferrules 21 and 22 are arranged at the remaining peripheral portions.

Further, the peripheral support band 11 as shown in FIGS. 2 to 6 is provided with a plurality of inwardly curved upwardly directed (downstream) projections 11a at intermediate positions of the adjacent fuel rods 5. is there. In addition, the peripheral support band 11 has a pair of outwardly protruding lobes near the four corners.
24 is also formed so as to have a constant space between it and the channel box 8 surrounding it.

The fuel spacer 19a shown in FIG.
Using 44 tubular ferrules 10, the fuel spacer 19 of FIG.
The fuel spacers are arranged in the same arrangement as that of b. The difference is that the swirl vanes 25 and their base members 24 are not provided with overhangs. As an example, the fuel spacers 19b in FIG. 5 are arranged below the fuel spacers 19c in the longitudinal direction of the fuel assembly 18, and one or more fuel spacers 19a are arranged below the fuel spacers 19c.

Next, the operation of the above configuration will be described. Cooling water, which is the coolant of the nuclear reactor, rises from below the core into the fuel assembly 18 loaded in the core. That is, the cooling water flows into the lower tie plate 4 from below,
Further, the flow path between the fuel rods 5 and 9 rises in the channel box 8 and flows out from the upper tie plate 3 to an upper plenum (not shown).

A part of the cooling water flowing into the channel box 8 is supplied into the water rod 6 through the cooling water inlet 6a, rises in the water rod 6 and flows out of the water rod 6 through the cooling water outlet 6b. To do. The water rod 6 increases the proportion of the cooling water in the central portion of the cross section of the fuel assembly 18, and has the function of increasing the neutron moderating action in the central portion. Therefore, the reactivity of the central portion of the cross section of the fuel assembly 18 becomes high, and the output distribution in the cross section is flattened.

By the way, the cooling water flowing in the channel box 8 removes heat from the fuel rods 5 and 9 as it rises in the axial direction, and is heated from the subcool state to the saturation temperature.
Furthermore, boiling of saturated water occurs. Therefore, of the two-phase flow coolant, ideally, the liquid phase (saturated water) flows near the fuel rod surface and the gas phase (steam) flows in the space between the fuel rods, which is the most effective heat removal. It will be good.

On the other hand, looking at the coolant flow pattern in the actual fuel assembly 18, in the upper half region of the fuel assembly having a high void ratio and a small margin for heat removal, there is a gas-liquid two-phase flow state called annular flow. Has become. In this flow state, as shown in the behavior explanatory diagram of the two-phase flow in the fuel assembly in FIG. 13, the void rate becomes high in the flow path 17 in the space between the fuel rods 5,
Droplets 30 mix and flow in it. The surface of the fuel rod 5 is covered with the liquid film 31, and the boiling of the liquid film 31 removes heat from the fuel rod 5.

Considering the two-phase flow state (presenting an annular flow state) of the cooling water after passing through the fuel spacers 19b and 19c in the present invention, the flow state as shown in the flow velocity distribution explanatory diagram of FIG. 14 is obtained. Be considered. That is, the fuel spacer 19
After passing b and 19c, the flow along the surface of the tubular ferrule 20 of the fuel spacers 19b and 19c is separated to generate turbulent flow.

Further, the droplet 30 attached to the side wall of the tubular ferrule 20 is scattered in the two-phase flow at the upper end of the side wall, and is attached to the surface of the fuel rod 5 due to the turbulent flow to increase the thickness of the liquid film 31. Contribute,
Furthermore, the flow path 17 surrounded by the outer surface of the side wall of four tubular ferrules
Droplets 30 in the vapor stream of the fuel collide with the swirl vane base member 24 or the swirl vane 25, fly on the flow of the two-phase flow deflected from the upper end of the swirl vane 25, and fly toward the surface of the fuel rod 5. . The droplets 30 in the vapor flow that have not adhered to the swirl vane 25 and the swirl vane base member 24 also ride on the deflected flow of the swirl vane 25 and come close to the surface of the fuel rod 5, resulting in no swirl vane 25. The amount of droplets adhering to the surface of the fuel rod is significantly increased as compared with the case.

In the above-mentioned Japanese Patent Laid-Open No. 2-285286, the swirl vane is provided directly on the side wall of the tubular ferrule, but the velocity distribution of this flow passage is as shown by the streamline on the left side of FIG. Since the center of the flow path 17 surrounded by the four rods has a higher speed, the efficiency of generating the swirling flow is poor from the viewpoint of causing the swirling flow to bring the droplet 30 closer to the fuel rod surface by the centrifugal force.

Further, moving the liquid droplets 30 floating in the center of the fuel rod flow path 17 to the outside in a swirling flow is less effective because the swirling flow is immediately attenuated in a short distance. However, the swirl vanes 25 of the present invention allow the droplets 30 in the two-phase flow to
Direct capture, splattering and large deflected flow can be made.

Further, in the above disclosed example, since the side wall of the fuel spacer continues in the axial direction to generate a swirl flow, most of the droplets in the vapor flow deflected by the centrifugal force are tubular ferrules. Although it adheres to the outer wall and then scatters from the upper end and adheres to the fuel rod surface, this indirectly results in an increase in droplet adhesion to the fuel rod surface. In JP 2-2852
Even if it is installed as shown in FIG.

However, the swirl vane 25 of the present invention is provided in the center of the fuel rod flow passage 17 and has the tubular ferrule 20.
Since it is positioned above the upper end of the side wall (projecting to the downstream side), the deposition of the droplet 30 by the deflected flow is directly on the surface of the fuel rod 5 and is efficient. To that extent, the balance sheet of the droplet adhesion effect and the increase of pressure loss is superior to the above-mentioned prior disclosed example.

This effect appears in the form that the effect of improving the limit output is greater with respect to the increase of the same pressure loss. Further, according to the present invention, the shape change of the tubular ferrule 20 with respect to the flow direction of the fluid is performed only by partially cutting and bending the side wall of the tubular ferrule 20, and it is easy to manufacture because there is no increase in new parts or assembly steps. Is. In the tubular ferrules 20 to 23 of the above-described embodiment, the projections 20a to 23a on the inner side of the upper portion are arranged at a distance further downward from the cutout position of the swirl vane base member 24, which is a feature of the present invention.

The second embodiment shown in the perspective view of FIG. 15 is different in that the projection on the inside of the upper portion is arranged immediately below the cut-out position of the swivel vane base member 24. Although FIG. 15 shows the basic shape of four swirl vanes 25, the tubular ferrule disposed around the fuel spacer has one swirl vane base member 24 and one swirl vane 25 as in the above-described embodiment. By preparing two pieces, the fuel spacers 19b and 19c as shown in FIGS. 5 and 6 can be easily constructed.

As a result, the axial length of the tubular ferrule 32 can be shortened, and there is an advantage that friction loss and parasitic neutron absorption of the fuel spacer can be reduced, but since the overhanging starting point of the swirl vane base member 24 is narrow, There is a weak point structurally weak by itself. However, this can be solved because the side wall thickness becomes two by welding the adjacent tubular ferrules.

A third embodiment in the case where the shape of the water rod is different is shown in the plan view of FIG. 16 and the plan view of the main part of FIG.
The basic shape of the tubular ferrule used in this example may be either the tubular ferrule 20 of FIG. 7 or the tubular ferrule 32 of FIG.

In the third embodiment, the water rod 33 of the square tube is combined, and the swirl vanes 25 of the tubular ferrules 20 and 32 adjacent to the square water rod 33 serve as guides during the insertion and assembly of the square water rod. Then, the liquid film flow adhering to the outer tube wall of the square tube water rod 33 is peeled off and adhered as droplets to the surface of the fuel rod 5 adjacent to the square tube water rod 33.

Therefore, in the structure of the tubular ferrule 32 with swirl vanes of the third embodiment, the inner support band 34 having the upward projections 34a and 34b as in the fourth embodiment shown in FIG. 18 is not provided separately. There is an advantage that can be done.

The fourth embodiment shown in the plan view of the essential parts of FIG.
FIG. 16 is a modification of the third embodiment shown in FIGS. 16 and 17, and shows the swirl vane base member 24 and swirl vane 25 of the tubular ferrules 21 and 22 adjacent to the square water rod 33 on the square water rod side. 10, a rectangular water rod of the above-mentioned tubular ferrule, which is not provided as shown in FIG.
An inner support band 34 is welded to the side facing 33, and a plurality of upward projections 34a curved outward (toward the downstream side) are formed at the upper end of the inner support band 34 at an intermediate position between fuel rods.
Provide 34b.

The upward projections 34a and 34b are provided in Japanese Patent Application No. 59-19.
It corresponds to the liquid film diffusion protrusion on the surface of a large water rod disclosed in Japanese Patent No. 6531, and its effect of improving the limiting output has been experimentally confirmed.

The embodiment of FIGS. 19 to 22 is a method different from the embodiment of FIG. 4 and the method of forming the tubular ferrule with a swirling vane shown in the modification thereof. 19 is a perspective view and FIG. 20.
In a fifth embodiment shown in a partially enlarged plan view of FIG. 5, a swirl vane is formed by cutting and bending the side wall end from the vicinity of the upper end (downstream side) of the tubular ferrule 35 diagonally at four places outward in the normal direction of the tubular ferrule side wall. The base member 24a is provided, and a swirl vane 25a extending obliquely upward is provided at the tip of the base member 24a by bending, and the swirl vane 25a has a shape protruding further downstream from the downstream end of the side wall of the tubular ferrule 35.

In this fifth embodiment, the swirl vane base member
Since 24a is shorter than the above-mentioned first and second embodiments and bends outward from the tubular ferrule side wall,
The amount of material is small, the parasitic neutron absorption of the fuel spacer is small, and it is advantageous in the neutron economy. Further, the characteristic of the swirl vane 25a is that the direction of the two-phase flow is deflected in the surface normal direction of the adjacent fuel rods 5, 9 as shown by the arrow 36 in FIG. This increases the probability that droplets in the two-phase flow will approach and stick to the fuel rod surface with a higher probability.

In the sixth embodiment shown in the perspective view of FIG. 21 and the partially enlarged plan view of FIG. 22, the swirl vanes 25a of the fifth embodiment are bent in a plane with respect to the base member 24a. In contrast, the swirl vane 25b has a tubular ferrule 37.
Bending while twisting outward. As a result, not only the direction of the two-phase flow is deflected in the surface normal direction of the adjacent fuel rods 5 and 9 as shown by the arrow 36 in FIG. Even more droplets in the two-phase flow can be deposited closer to the fuel rod surface.

In the fifth and sixth embodiments, only the basic shapes of the tubular ferrules 35 and 37 having four swirl vanes are shown. However, when the tubular ferrules 35 and 37 are put together into a fuel spacer shape, the above-mentioned one embodiment is carried out. One swirl vane as in the example,
It can be easily realized by preparing only two pieces and combining them by welding.

The tubular ferrule 20 with swirl vanes described in the above embodiments can be easily made of zirconium alloy such as Zircaloy-2, 4 swirl vane base members 24, 24a, 24.
b and swirl vanes are cut at the stage of a cylindrical tube or octagonal tube by a method such as electric discharge machining, laser machining, or press working, and then bent outward by a press to easily open to a predetermined shape. , Further swirl vanes 25,
It can be integrally processed by bending the portions 25a and 25b.

As a result, for example, in the portion of the flow path 17 surrounded by the four tubular ferrules 10 as shown in the explanatory view of FIG.
Compared to the structure in which the swirl vane assembly 39 in which two swirl vane materials 38 are assembled in a cross shape is inserted so that the swirl vanes 25 project to the downstream side and welded, the number of parts can be reduced and the fuel spacer can be assembled and processed. It will be easier.

FIG. 24 relates to the seventh embodiment. In the enlarged perspective view of FIG. 24 (a), a twisting blade 40 is mounted as a swirling vane at the downstream portion (upper end) of the gap between the four tubular ferrules 10. Here is an example. The advantage of using the twisting blade 40 is that the central portion of the sub-channel flow path where the coolant velocity is faster has a smaller angle of the blade with respect to the coolant flow, and therefore the increase in pressure loss due to the arrangement of the twisting blade is small. To be

Furthermore, since the flow path in the tubular ferrule 10 is not narrowed by applying the twist above the upper end of the tubular ferrule 10, the increase in the pressure loss of the fuel spacer portion due to the installation of the torsion blade 40 is minimized. A swirl flow can be generated in the coolant. Also twisted wings
Torsion blade 40 to prevent contact with fuel rods due to vibration of 40
The upper end of is rounded.

The twisted blades 40 are
Since a force is applied in the flow direction and a swirl flow is generated in the coolant, the reaction force is also received. Therefore, when the strength is insufficient only by welding, as shown in the enlarged perspective view of FIG. Is provided on the upper side surface of the lower end of the torsion blade 40, and the lower end convex portion 40a is provided on the lower side of the torsion blade 40.
The torsion blade 40 may be fixed by fitting it into b and welding it. With this method, compared with the case of welding only,
40 can be mounted firmly.

The front view of FIG. 25A and the side view of FIG. 25B show examples of twisted blades twisted by 180 degrees. These twisted wings 40 are fixed to the tubular ferrule 10 by welding,
Alternatively, the same mounting as in FIG. 24 may be performed.

The steam flow characteristic diagram of FIG. 26 shows the cross-sectional shape and flow of the swirling vane and the twisted blade. Steam flow 41
26. If the swirl vanes 25, 25a, 25b or the twisted blades 40 have a linear shape as shown in FIG. 26 (a), the steam flow 41 is easily separated on the upper surface of the blades, and a strong swirl flow 42 can be generated. Not only can it not be done, but it also increases pressure loss. However, as shown in FIG. 26 (b), the swirl vanes 25, 25a, 25b or the twisted blades 40 are curved to generate a strong swirl force.
Since 42 can be generated and the vapor flow 41 is less likely to be separated from the blade surface, an increase in pressure loss can be suppressed to a small level.

The characteristic diagram of FIG. 27 shows the relationship between the swirl vane and the angle of attack of the twisted blade with respect to the steam flow, and the swirl force and the drag force. The angle at which the turning force is maximized is called the stall angle. When the angle of attack is set to be less than or equal to the stall angle, the drag force is small, so that the pressure loss does not increase so much and the swirling flow can be effectively generated.

For example, in the case of an airplane wing, the stall angle of a flat plate wing is several degrees, but the stall angle is increased and the lift is increased by curving the wing surface to form a streamline shape with a distribution in thickness. ing. Therefore, the torsion blade 40 and the swirl vane of the present invention
Also for 25, by curving the cross-sectional shape instead of a straight line,
The pressure loss due to the installation of the torsion blade 40 can be minimized, and the swirling force of the coolant can be increased.

The enlarged perspective view of FIG. 28 shows the same advantage as the twisted blade, and the pressure at which the vane angle with respect to the coolant flow is made smaller toward the center of the coolant flow passage surrounded by four fuel rods with high coolant flow velocity. An example in which a swirl vane 40 with a small loss increase is provided at the upper end of the passage surrounded by the four tubular ferrules 10 is shown.

29 (a), (b) and (c) show an assembly view, a plan view and a perspective view of the swirl vane shown in FIG. In this example of the turning vane, the turning vane 40 is assembled in a cross shape as shown in FIG. 29 (a), and further four corners of the downstream end of the turning vane 40 are bent in the same rotation direction to form the turning vane. .

The characteristic of this swirl vane is that it can be easily formed because it can be formed only by bending without twisting with a large degree of processing, and it is surrounded by four fuel rods with a high coolant flow rate like a torsion blade. Since the vane angle with respect to the coolant flow is smaller in the central portion of the formed coolant flow path, there is an advantage that the increase in pressure loss is small.

The partially enlarged plan view of FIG. 30 shows an example in which a torsion blade 40 is attached to the upper part of the flow path of four tubular ferrules 10.
According to the seventh embodiment, in the fuel spacer composed of the cylindrical tubular ferrule 10 which has been used so far, the liquid droplets 30 that flow along with the vapor flow that has not been effectively used for cooling the fuel rods 30. As shown in the behavior explanatory diagram of FIG. 31, the swirling flow is generated in the fuel rod flow passage 17 formed by the four fuel rods 5.
By raising 43, it is possible to turn it toward the fuel rod 5 side by centrifugal force.

Further, the twisting blade is provided at the upper portion (downstream side) of the fuel spacer, not at the portion where the flow passage area of the fuel spacer portion is reduced.
By adding 40, it is possible to minimize the disturbance of the liquid film 31 on the surface of the fuel rod upstream of the fuel spacer. Further, by making the twisted portion of the twisting blade 40 extend above the upper end of the fuel spacer portion, the flow passage area of the fuel spacer portion is almost the same as that of the fuel spacer without the twisting blade.

Further, by accurately setting the twist angle and the blade shape of the twisting blade 40, the increase in the pressure loss of the fuel spacer portion due to the addition of the twisting blade 40 can be minimized, and it can be effectively used as a coolant. It is possible to generate a special swirling flow 43 and direct the droplets 30 in the vapor toward the fuel rod 5. Therefore, as compared with the conventional fuel, the increase in pressure loss is slight, but as shown in the comparative characteristic diagram of FIG. 32, the fuel assembly according to the present invention is compared with the conventional fuel assembly in which the torsion blades are not arranged. The critical power to reach the boiling transition of is improved.

The direction in which the twisting blades 40 rotate the steam may be mainly the pattern of the swirling flows 43 and 43a as shown in the plan views of FIGS. 33 and 34. In both patterns, the interaction between the sub-channels is considered to be small, and therefore the marginal output improving effect is considered to be almost the same. However, Figure 34
In the case of the pattern of, since it is necessary to create two types for the right rotation and the left rotation of the twisting blade 40 or the swirl vane 25,
As shown in the pattern of FIG. 33, the same swirling flow 43 in the rotating direction requires fewer kinds of parts.

The perspective view of FIG. 35 shows an eighth embodiment. This tubular ferrule 44 is formed by integrally molding a tubular ferrule member and a swirl vane 25.As shown in the development view of FIG. 36, a swirl vane 25 having a convex shape is formed on the downstream side of the member of the tubular ferrule 44 and further cut. By inserting 44b, molding can be performed as shown in the plan view of the main part of FIG. 37. By combining a plurality of tubular ferrules 44, the swirl vane 25 can be easily provided in the downstream portion of the tubular ferrule 44. A twisted blade can also be formed by twisting the convex swirl vane 25.

Considering an increase in droplet adhesion to the fuel rod surface on the downstream side of the fuel spacer and an increase in pressure loss due to the fuel spacer due to the fuel spacers 19b and 19c constituted by the tubular ferrule 20 with swirling vanes, etc. The swirl vane-equipped fuel spacer of the present invention need not be adopted for all of the fuel spacers provided in the axial direction of the fuel assembly.

That is, a normal fuel spacer 19a having no swirl vane is arranged in the lower stage of the fuel assembly 18 in which the pressure loss is a more important factor to be taken into consideration. The upper part of the fuel assembly 18 where
It is desirable to arrange b and 19c.

For example, according to the experimental data so far,
Since it is known that the axial position of the fuel spacer that causes the boiling transition is near the upstream side of the uppermost fuel spacer or the second uppermost fuel spacer in the case of seven fuel spacers, at least 1 The second and third stages are the fuel spacers 19b and 19c with the swirl base of the present invention, and the fuel spacers in the lower stages are the fuel spacers 19 without swirl vanes.
It can be considered to be a.

Further, the fuel spacer with swirl vanes according to the present invention may be adopted as a part of the lower fuel spacer. As a fuel spacer without swirl vanes, the above-mentioned FIG. 42, FIG.
6 and FIG. 2 to Fi of Japanese Patent Laid-Open No. 2-290594, which is called an egg crate type instead of the structure shown in FIG.
A fuel spacer that prioritizes low pressure loss as disclosed in g.4 may be used.

When the axial spacing of the fuel spacers in the upper part of the fuel assembly is narrowed to increase the number of fuel spacers, the limit output can be improved accordingly. It may be considered to reduce the number of the fuel spacers 19b and 19c with swirling vanes from the top to only one or two stages.

Further, recent fuel assemblies have a design in which a blanket region is formed by using natural uranium, recovered uranium, and concentrated waste uranium at the upper end of the active fuel length, but the quality of the coolant is high in this region. However, the heat generation of the fuel rod 5 is small and the heat flux is small. Therefore, boiling transition does not occur on the downstream side of the uppermost fuel spacer located in this portion, so that the uppermost fuel spacer has a normal fuel spacer 7b without a swirl vane or other low pressure loss characteristics. It may be used as a fuel spacer.

The fuel spacer arrangement conceptual diagram of FIG. 38 more concretely shows various embodiments of the fuel assembly 18 according to the present invention. It should be noted that this embodiment shows the case where seven fuel spacers are used for the fuel heating portion, but the present invention is not limited to this embodiment.

In FIG. 38 (a), all seven fuel spacers have swirl vanes according to the present invention, as shown by hatching, or
The structural example of the fuel assembly using the fuel spacers 19b and 19c with a torsion blade. In (b), the fuel spacers 19b and 19c according to the present invention are used for the six fuel spacers on the upstream side of the fuel channel, and the fuel spacer on the most downstream side reduces the pressure loss of the fuel heating portion and improves the channel stability. A configuration example of a fuel assembly using the conventional fuel spacers 7b and 19a in consideration of improvement.

(C) is a fuel assembly using the conventional fuel spacer 19a at the upstream 1/3 position of the fuel heat generating portion and the fuel spacers 19b, 19c according to the present invention at the downstream 2/3 position. Body configuration example. (D) is a structural example of a fuel assembly in which the examples of (b) and (c) are combined. Although the fuel spacers 19a and 19b according to the present invention and the conventional fuel spacers 7b and 19a are combined in these embodiments, they may be combined with other low pressure loss type fuel spacers.

As in the case of this example (d), the same fuel spacers 7b and 19a as the conventional one were used as the fuel spacers at the most downstream position of the fuel assembly and the upstream side of the fuel heat generation center, and the most downstream position was removed. Tubular ferrule fuel spacers 19b and 19c with swirl vanes or twisted blades are used for the three fuel spacers on the downstream side from the center of the fuel heating portion.

Since the swirl vanes or the twisting vanes guide the liquid droplets in the steam to the surface of the fuel rod, it is effective if they are mounted only on the fuel spacer in the flow mode position called the tubular flow in which the steam is the main flow. It is enough. Further, the boiling transition is likely to occur immediately below the fuel spacer located in the most downstream or the fuel spacer located in the second stage from the most downstream.
It is not necessary to attach torsion wings or the like.

The grid shape of the fuel spacer has been described by taking the example of two water rods of 9 × 9 grid, but even if the number of water rods 6 or the shape is different,
Further, the tubular ferrule with a swirl vane of the present invention can be applied to other shapes such as an 8 × 8 lattice, and the same effect can be obtained.

Further, although the tubular ferrules so far have been described based on the cylindrical tubular shape, the perspective view and the diagram of FIG.
As shown in a partially enlarged plan view of 40, a similar tubular ferrule with a swirl vane can be configured also in an octagonal tubular ferrule 45 having an octagonal cross section.

Further, although the fuel spacers of the square lattice fuel rod array have been described in the above embodiments, the downstream side end portion is also used in the case of using the cylindrical tubular ferrule for the triangular lattice fuel rod array. Of the adjacent tubular ferrules, the two-phase flow of the part forming the flow path surrounded by the outer surface of the tubular ferrule side wall by slewing the swivel vane base member tangentially from the peripheral edge of the tubular ferrule and providing the swirl vane at the upper end thereof. This can be easily realized by deflecting and adhering the liquid droplets on the fuel rod surface.

In addition, there are the following items as embodiments of the above claims. (1) "The swirl vane extends to the vicinity of the center of the flow path surrounded by four fuel rods, and the swirl vane base member protruding from the adjacent tubular ferrule forms a cross shape around the flow path center. The fuel spacer according to claim 1.

(2) “In a fuel spacer in which a plurality of fuel rods are regularly arranged and a plurality of fuel rods are inserted to keep the fuel rods at proper intervals, a swirl vane and a base member formed on the tubular ferrule are attached to an axis of the tubular ferrule. The method for manufacturing a fuel spacer according to claim 1, wherein a part of the side wall is cut open from the upper end in the direction and bent and integrally processed.

(3) "A fuel assembly characterized in that the fuel spacer according to any one of claims 1 to 3 is used as a fuel spacer excluding the fuel spacer located on the most downstream side of the fuel heating portion." (4) ) "A fuel assembly characterized by using one or more fuel spacers according to claims 1 to 3 as a fuel spacer at a position ⅔ on the downstream side of a fuel heat generating portion."

[0110]

As described above, according to the present invention, the tubular ferrule is provided with a swirling vane or a twisted vane having a simple shape to improve the flow of the coolant at the fuel spacer position and suppress the increase of the pressure loss. Since the cooling effect on the fuel rods is improved, there is an effect that the limit output of the fuel assembly in which the fuel spacer is effectively adopted can be improved.

[Brief description of drawings]

FIG. 1 is a partially cut front view of a fuel assembly according to an embodiment of the present invention.

FIG. 2 is a partially cutaway front view of a fuel spacer according to an embodiment of the present invention.

FIG. 3 is a partially cut front view of a conventional fuel spacer.

FIG. 4 is a plan view of a fuel spacer taken along the line C-C in FIG. 1.

5 is a plan view of the fuel spacer according to the present invention as viewed from the direction of arrows D-D in FIG. 1. FIG.

FIG. 6 is a plan view of the fuel spacer according to the present invention as viewed in the direction of arrows EE in FIG.

FIG. 7 is a perspective view of a tubular ferrule according to an embodiment of the present invention.

FIG. 8 is a partially enlarged plan view of the fuel spacer according to the embodiment of the present invention.

FIG. 9 is a plan view of an essential part of a fuel spacer according to an embodiment of the present invention.

FIG. 10 is a perspective view of a tubular ferrule according to an embodiment of the present invention.

FIG. 11 is a perspective view of a tubular ferrule according to an embodiment of the present invention.

FIG. 12 is a perspective view of a tubular ferrule according to an embodiment of the present invention.

FIG. 13 is an explanatory view of the behavior of two-phase flow in the fuel assembly.

FIG. 14 is an explanatory view of a flow velocity distribution on the downstream side of the fuel spacer according to the present invention.

FIG. 15 is a perspective view of a tubular ferrule according to a second embodiment of the present invention.

FIG. 16 is a plan view of a fuel spacer for a rectangular tube type water rod according to a third embodiment of the present invention.

FIG. 17 is a plan view of a main portion of a fuel spacer of a rectangular tube type water rod according to a third embodiment of the present invention.

FIG. 18 is a plan view of an essential part of a modification of the fuel spacer of the square tube water rod according to the present invention.

FIG. 19 is a perspective view of a tubular ferrule according to a fifth embodiment of the present invention.

FIG. 20 is a partially enlarged plan view of the fuel spacer according to the fifth embodiment of the present invention.

FIG. 21 is a perspective view of a tubular ferrule according to a sixth embodiment of the present invention.

FIG. 22 is a partially enlarged plan view of the fuel spacer according to the sixth embodiment of the present invention.

FIG. 23 is an explanatory view of an assembling flow of the cross swirl vane.

24A and 24B are enlarged perspective views of a twisting blade portion of a fuel spacer of a seventh embodiment according to the present invention, and FIG. 24B is an enlarged perspective view of a fitting groove portion.

FIG. 25 (a) is a front view of the twisted wing according to the present invention,
(B) is a side view.

FIG. 26 is a characteristic view of a cross-sectional shape of a swirl vane and a twisted blade and steam flow ((a) is a straight blade, (b) is a streamlined blade).

FIG. 27 is a characteristic diagram of the attack angle of the swirl vane and the twisted blade, and the swirl force and drag.

FIG. 28 is an enlarged perspective view of the twisted wing portion of the fuel spacer according to the present invention.

29A and 29B are perspective views of the twisted blade according to the present invention for explaining assembly, FIG. 29B is a plan view, and FIG. 29C is a perspective view.

FIG. 30 is a partially enlarged plan view of the fuel spacer according to the seventh embodiment of the present invention.

FIG. 31 is an explanatory diagram of behavior of a swirling flow and a droplet.

FIG. 32 is a comparative characteristic diagram of the limit output.

FIG. 33 is a plan view showing a unidirectional swirling flow in a fuel assembly according to the present invention.

FIG. 34 is a plan view showing a bidirectional swirling flow in a fuel assembly according to the present invention.

FIG. 35 is an enlarged perspective view of an essential part of a tubular ferrule according to an eighth embodiment of the present invention.

FIG. 36 is a developed front view of the tubular ferrule according to the eighth embodiment of the present invention.

FIG. 37 is a plan view of a main part of the tubular ferrule mounting assembly according to the eighth embodiment of the present invention.

FIG. 38 is a conceptual diagram showing an arrangement example of fuel spacers in the fuel assembly according to the present invention.

FIG. 39 is a perspective view of an octagonal tubular ferrule according to the present invention.

FIG. 40 is a partially enlarged plan view of a fuel spacer using the octagonal tubular ferrule according to the present invention.

FIG. 41 is a partially cut front view of a conventional fuel assembly.

42 is a plan view of the conventional fuel spacer, taken along the line AA in FIG.

43 is a plan view of the conventional fuel spacer as viewed from the direction of arrows B-B in FIG. 41.

FIG. 44 is a perspective view of a conventional tubular ferrule.

FIG. 45 is an enlarged perspective view of a main part of a conventional fuel spacer.

FIG. 46 is a partially enlarged plan view of a conventional fuel spacer.

FIG. 47 is a flow velocity distribution diagram of the flow path between fuel rods.

[Explanation of symbols]

1, 18 ... Fuel assembly, 2 ... Handle, 3 ... Upper tie plate, 4 ... Lower tie plate, 5 ... Fuel rod, 6 ... Water rod, 6a ... Cooling water inlet, 6b ... Cooling water outlet, 7a, 7b, 9a ... Fuel spacer, 8 ... Channel box, 9 ... Short fuel rod, 10, 20, 21, 22, 23, 32,
35, 37, 44 ... Tubular ferrule, 10a, 20a, 21a, 22
a, 23a, 32a, 35a, 37a, 44a, 45a ... Inner protrusion,
10b ... Fitting groove, 11 ... Peripheral support band, 11a, 34a,
34b ... Upward protrusion, 12 ... Spot welding, 13,29 ... Continuous loop spring, 14 ... Notch part, 15 ... Claw part, 16 ... 45 degree direction fuel rod surface part, 17 ... Fuel rod flow path, 19b, 19c ... Fuel spacer with swirl vane, 24 ... Lobe, 24a ... Swirling vane base member, 2
5, 25a, 25b ... Swirl vanes, 26 ... Holes in the central portion of the fuel spacer, 27a, 27b ... Bridging members, 28 ... Bent portions, 30 ... Droplets, 31 ... Liquid film, 33 ... Square tube water rod, 35 ... Fuel spacer inner band, 36 ... Two-phase flow deflection direction (arrow), 38
... Swirl vane material, 39 ... Swirl vane assembly, 40 ... Torsion blade, 40a ... Lower end convex portion, 41 ... Steam flow, 42 ... Swirl force, 43, 43
a ... swirling flow, 44b ... notch, 45 ... octagonal tubular ferrule.

Claims (5)

[Claims] 1. A fuel spacer for holding a fuel rod in a lateral position at a predetermined position by connecting tubular ferrules through which each of a plurality of fuel rods including a water rod is inserted, to a side wall upper end (coolant) of the tubular ferrule. The downstream end of the tubular ferrule extends outward from the tubular ferrule to form a swirl vane that extends obliquely upward at the tip, and the swirl vane projects further downstream than the downstream end of the side wall of the tubular ferrule. Fuel spacer to do. 2. A fuel spacer for connecting a plurality of fuel rods, including water rods, to each other to connect tubular ferrules to hold the fuel rods in place laterally, formed by the sidewalls of adjacent tubular ferrules. A twisted blade that is twisted in a direction perpendicular to the coolant flow is disposed on the central axis of the center of the coolant passage on the downstream side of the upper end of the tubular ferrule side wall (downstream side of the coolant). And fuel spacer. 3. A fuel spacer for connecting tubular ferrules through each of a plurality of fuel rods, including water rods, to hold the fuel rods in place laterally, formed by the sidewalls of adjacent tubular ferrules. A fuel spacer characterized in that a twisting blade having a central axis at the center of the coolant passage is formed so as to project from the tubular ferrule side wall on the downstream side of the upper end (coolant downstream side) of the tubular ferrule side wall in the formed coolant passage. 4. A fuel assembly in which a plurality of fuel rods, each of which is surrounded by a channel box and which is supported by an upper tie plate and a lower tie plate, is laterally arranged and held by a fuel spacer arranged in a plurality of stages in a longitudinal direction. A fuel assembly, wherein the fuel spacer is the fuel spacer according to any one of claims 1 to 3. 5. A fuel assembly in which a plurality of fuel rods, each of which is surrounded by a channel box and supported by an upper tie plate and a lower tie plate, is arranged in a lateral direction by a fuel spacer arranged in a plurality of stages in a longitudinal direction. The fuel assembly according to any one of claims 1 to 3, wherein at least the second or third fuel spacer counted from the uppermost stage is the fuel spacer according to any one of claims 1 to 3.