JPH08122474A - Fuel spacer and fuel assembly - Google Patents

Abstract

PURPOSE: To provide a fuel spacer and a fuel assembly that can efficiently apply liquid drops to fuel rods, many of which exist beside the inner face of a channel box, has a simple structure and can contribute greatly to the improvement of the limit output. CONSTITUTION: This fuel spacer has a supporting band 11 formed like a square frame to support a bundle of fuel rods 3 from the direction of the outer circumference and a fuel holding part 16 placed in connection with the inside of the supporting band 11 to hold each of the fuel rods 3 arranged in a lattice at some intervals. In a channel box whose section is square, coolant passages are longitudinally formed between the channel box and the fuel rods and between fuel rods. An inclining flow tub 12 for turning the coolant flow toward the fuel rods 3 is placed at the edge at least on the downstream side of the coolant flow in a supporting band 11. A section has a shape equipped with an edge 17 for controlling the inflow from the direction intersecting that of the coolant flow to a face 12a on the downstream side of the coolant flow in the flow tub 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel spacer that is incorporated in a fuel assembly of a nuclear reactor to hold fuel rods at appropriate intervals, and a fuel assembly that incorporates the fuel spacer.

[0002]

2. Description of the Related Art Recent water-moderated nuclear reactors, especially the mainstream light-water reactors, are designed to reduce the operating cost of nuclear power plants, operate in a long-term cycle, and to economically burn fuel to realize these operations. A fuel assembly having a non-uniform shape in the radial direction is introduced.

FIG. 44 shows the structure of a fuel assembly used in a boiling water reactor (BWR) as an example of such a fuel assembly. That is, in this fuel assembly 1, large diameter water rods 4 corresponding to four fuel rods 3 are arranged at the center of a channel box 2 which is a tubular flow path having a substantially quadrangular cross section, and 60 are provided around it. The fuel rods 3 of the book are arranged in a square lattice shape as a whole.

A cooling water inflow hole 5a and a cooling water ejection hole 5b are formed at the upper and lower ends of the water rod 4. A plurality of fuel spacers 7 are arranged in the axial direction in order to maintain a constant horizontal interval between the fuel rods 3, the water rods 4, and the short fuel rods 6 arranged in a square lattice.

Further, a bundle of fuel rods 3, water rods 4 and short fuel rods 6 bundled by a fuel spacer 7 is surrounded by a channel box 2. The channel box 2 is attached to the upper tie plate 8 and covers the outer surface of the lower tie plate 9. In the figure, reference numeral 10 is an external spring inserted in the upper end plug of the fuel rod 3 in contact with the lower surface of the upper tie plate 8.

FIG. 45 is an enlarged view of the fuel spacer 7 shown in FIG. 44, showing a state in which the fuel rod 3 is inserted. The fuel spacer 8 has a rectangular frame-shaped support band 11 that supports the bundle of fuel rods 3 from the outer peripheral side, and a fuel rod insertion passage that is continuously provided in the support band 11 and that allows the fuel rods 3 and the short fuel rods 6 to pass therethrough. Each has an annular ferrule as a fuel holding portion formed independently. The annular ferrules are bundled in the same number as the fuel rods 3 and the short fuel rods 7 arranged in a lattice, and the outer periphery of the bundle of the annular ferrules is surrounded by the support band 11, and the fuel spacer 7 is constituted by this. .

Further, a protrusion 11a is formed on the outer surface of the support band 11 so that the bundle of the fuel rods 3 does not deviate significantly in a specific direction of the channel box 2 and further downstream of the coolant flow of the support band 11. The flow tab 12 is provided so as to project from the upper edge portion which is the side.

The coolant flowing in the channel box 2 is heated by the fuel rods 3 as it rises in the channel box 2 from the lower part, and is boiled to form a gas-liquid two-phase flow composed of a liquid phase and a gas phase. To pass. At that time, the gas phase mainly flows in a relatively wide flow path between the fuel rods 3, part of the liquid phase flows together with the gas phase, and part of the liquid phase flows on the surface of the fuel rods 3 and the inner surface of the channel box 2. As a liquid film flow.

When the liquid phase flowing along the surface of the fuel rod 3 decreases, the surface heat transfer coefficient of the fuel rod 3 decreases (boiling transition start) and overheating (burnout) may occur. The thermal limit of the fuel assembly 1 is a state of transition from the nucleate boiling region H1 to the transition boiling region H2 on the boiling curve L shown in FIG. 46, and the heat flux at that time is defined as the limit heat flux qCHF. The boiling mode during normal operation is the nucleate boiling region H1, which is in a stable state, and the fuel rod surface (cladding tube surface) temperature is kept constant at a temperature of several degrees higher than the saturation temperature of the coolant. Be done.

On the other hand, when the burnout point A is exceeded, the difference (superheat degree) between the fuel rod surface temperature and the coolant saturation temperature gradually increases, resulting in a boiling state in which heat transfer is unstable. The burnout point A is not a limit point that actually causes thermal damage to the cladding tube, but is a boiling region which is not allowed as a fuel rod during normal operation and transient change of a single failure. It is experimentally known that the burnout point A depends on parameters such as pressure, coolant flow rate, fuel assembly shape, axial power distribution, and nuclear fuel rod power distribution.

Further, it is known that the axial position where burnout occurs is within a few cm upstream from the lower end of the fuel spacer arranged in a region having a high void ratio.

The cause of this is the fuel rod 3 shown in FIG.
The coolant that has risen in the annular flow path between
Due to the flow resistance of the fuel rod, turbulence is generated on the fuel rod side, and due to this turbulence, a part of the liquid film flow adhered and formed on the fuel rod surface is separated (dry out), and the heat transfer coefficient of the separated part is reduced. It is thought to be because.

What is currently used as an index relating to the thermal margin of the core is a minimum power ratio (MCPR) as shown in the following equation.

[0014]

## EQU1 ## MCPR = QCP / QBUNDLE (1) where QBUNDLE: fuel assembly operation output, QC
P: Thermal limit output.

The minimum limit power is shown in FIG.
Take the locus as shown in. Since it is necessary to increase the concentration of the nuclear separation nuclide in the fuel rod with the long-term cycle operation,
As shown in Fig. 7, the thermal margin of the core tends to decrease after refueling. Therefore, in order to reduce the operating cost of a nuclear power plant, a fuel assembly design with a high thermal limit output is required, and a hard design (fuel spacer,
This is one of the purposes of fuel rods) and soft design (fuel enrichment distribution, combustion management, etc.).

In order to design a fuel assembly having a high thermal limit output, a method of increasing the limit output has been conventionally devised from the following viewpoints.

(A) Supply of Liquid Phase to Fuel Rod Surface by Mixing Coolant (b) Reduction of Heat Flux per Unit Surface of Fuel Rod From such knowledge, in the fuel assembly design corresponding to (a), In order to increase the cooling efficiency by increasing the proportion of the coolant used for cooling the fuel rods, means have been devised for directing the liquid phase flowing on the surface of the channel box, which does not contribute to the cooling of the fuel rods, to the fuel rods. There is.

One of them is a flow tripper (Japanese Patent Laid-Open No. 44289/1990) that separates a liquid film by providing a groove in a channel box to form a step, and a lateral velocity is applied to a liquid phase flowing on the surface of the channel box. By giving, it has the effect of increasing the proportion of coolant used to cool the fuel rods. However, since the step of the channel box increases the pressure loss of the fuel assembly and decreases the two-phase flow velocity near the channel box, the amount of droplets generated by the step is small and the marginal output improving effect is small. .

There are the following two points in the mixing effect (mixing effect) of the coolant in the fuel assembly.

(1) Transverse Transport by Average Flow (Forced Transverse Flow to Coolant) (2) Transverse Transport by Turbulent Mechanism The above-mentioned flow tripper is a method corresponding to (1). , (2) is not intended to be a positive effect. Further, in the fuel assembly design corresponding to (b),
It has been devised to reduce the diameter of the fuel rods to increase the surface area of the fuel rods and reduce the heat flux per unit surface area, and a design has been devised to increase the number of fuel rods such as 9 × 9.

On the other hand, the fuel spacer 7 is a constituent element of the fuel assembly that influences the thermal limit output of the fuel assembly. A plurality of fuel spacers 7 are installed in the height direction of the fuel assembly 1, and hold a gap between the fuel rods 3 and the water rods 4 and a gap between the channel box 2 and the fuel rods 3 and the water rods 4, The shape of the fuel assembly 1 is maintained. The following points (1) to (10) are generally considered in the fuel spacer design.

(1) Seismic resistance of fuel assembly (2) Maintenance of fuel rod spacing (3) Suppression of fuel rod vibration (4) Allowance for thermal expansion of fuel rod (5) Ease of assembly of fuel assembly (6) ) Minimization of contact area with fuel rods (7) Maximization of thermal limit output (8) Minimization of fuel assembly pressure loss (9) Minimization of parasitic neutron absorption (10) Minimization of the number of parts As an effect of the fuel spacer 7 on the dryout,
The mainly considered point is the effect of mixing droplets to the liquid film on the fuel rod surface by mixing the coolant (mixing effect).

From this knowledge, as the design element of the fuel spacer 7, the thickness of the fuel spacer is increased, or, as shown in FIG. 45, a large number of inward projections (flow tabs 12) are provided on the upper portion of the fuel spacer. There is. The flow tab 12 on the upper portion of the fuel spacer 7 is originally provided as an introduction portion when the fuel assembly 3 is inserted into the channel box 2. However, the mixing effect of the fuel spacer 7 is promoted and the thermal limit output is increased. Is known to contribute to the increase of That is, the flow tab 12 is provided at the downstream edge of the coolant flow of the fuel spacer 7.
The coolant flowing from the upstream side (lower part) of the fuel spacer is directed to the fuel side, thereby also having a role of improving the thermal margin of the fuel rod 3 located at the outermost periphery.

[0024]

In the conventional fuel spacer 7 described above, the upper end of the flow tab 12 is bent inside the fuel flow path portion, and as shown in FIGS. 3, the coolant flowing in the gap between the support band 11 and the support band 11 is biased to the fuel rod 3 side, and more of the coolant in the fuel rod gap is biased to the fuel rod side to effectively flow the fuel thermally. Improve the margin.

However, since the channel box 2 is a non-heat generating wall, as shown in FIG. 50, the attached liquid phase does not evaporate and becomes a liquid film 13, which flows along the wall surface of the channel box 2. Further, on the surface of the liquid film 13, the droplet 14
Is generated, the number of droplets 14 is relatively large. Flow tab 1
2 has such a relatively large amount of droplets 14 that the upper end of the flow tab 12 is bent inside the fuel flow path as shown in FIGS. 51 and 52. Due to the generation of the negative pressure region 15 at the downstream side, the droplet 14 near the inner wall of the channel box 2 is thrown toward the negative pressure region 15 and adheres to the fuel rod 3 due to the inertia, and the heat removal performance of the fuel rod 3 is improved. It is thought to improve. The above is considered to be the mechanism for improving the thermal margin of the outermost peripheral fuel rod by the flow tab 12.

53 to 56 show a conventional fuel spacer 7.
The structure and operation of the flow tab 12 in FIG.

As shown in FIG. 53, the flow tab 12 is conventionally formed in a flat plate shape, and as shown in FIG.
In addition to the flow of the coolant passing between the channel box 2 and the flow tab 12, the coolant is also wound from the side of the flow tab 2 (the direction intersecting the flow direction of the coolant) to the surface 12a of the flow tab 12 on the downstream side in the coolant flow direction. Because of the flow
Negative pressure level and area do not necessarily increase.

Further, as shown in FIG. 54, since the flow tab 12 has a flat plate shape in the related art, the droplets captured on the upstream surface 12b (lower surface) are distributed in the straight traveling direction a and the dispersion direction b, and b The liquid droplets in the direction contribute to the cooling of the fuel rod 3, but the liquid advancing in the direction a hardly contributes to the cooling of the fuel rod.

Further, as shown in FIGS. 55 and 56, in the conventional fuel spacer, the fuel rod 3 of the flow tab 12 is used.
Since the projected area along the longitudinal direction is small, a part of the coolant flowing in this portion passes as it is (arrow c) and does not contribute to the cooling of the fuel rod. That is, the flow tab 12 of the conventional fuel spacer 7 mainly acts on the two-phase flow flowing inside the fuel spacer to bring about a mixing effect, but the action on the two-phase flow flowing outside the outer periphery of the fuel spacer is small.

As described above, a large amount of liquid phase forming a liquid film flow exists on the inner surface of the channel box, but its contribution to cooling the fuel rod is small. Therefore, if the liquid film flow on the surface of the channel box can be directed to the cooling of the fuel rod, it is considered that the cooling effect of the fuel rod is increased.

In order to positively utilize such an effect, there has been proposed another means in the past.
There is a flow skirt such as -44289. This is based on the assumption that a protrusion is provided outward at the lower end of the outer periphery of the fuel spacer to separate the liquid film flow on the surface of the channel box and carry it to the flow inside the outer periphery of the fuel spacer. However, the effect between the projection and the channel box is questioned because they cannot be sufficiently close to each other in order to prevent damage due to hydrodynamic vibration.

The present invention has been made in view of the above circumstances, and an object thereof is to efficiently direct liquid droplets, which are often present in the vicinity of the inner surface of the channel box, to the fuel rod, and further, the structure is simple and limited. It is an object of the present invention to provide a fuel spacer and a fuel assembly that can greatly contribute to improvement of output and the like.

[0033]

In order to achieve the above object, the invention of claim 1 is a support frame of a rectangular frame shape for supporting a bundle of a plurality of fuel rods from the outer peripheral side, and an inner side of the support band. And a fuel holding portion that holds the fuel rods in a grid-like arrangement so as to be spaced apart from each other, and is arranged in a channel box having a quadrangular cross section between the channel box and the fuel rods and between the fuel rods. A fuel spacer that forms a coolant flow path along a direction, in which at least an edge portion of the support band on the downstream side of the coolant flow is provided with an inclined flow tab for directing the flow of the coolant toward the fuel rod, It is characterized in that the surface of the flow tab on the downstream side of the coolant flow has a sectional shape with an edge that suppresses inflow from a direction intersecting the coolant flow direction.

According to a second aspect of the present invention, a square frame-shaped support band for supporting a bundle of a plurality of fuel rods from the outer peripheral side, and the fuel rods which are continuously provided inside the support band and are held in a lattice-like arrangement in a separated manner. And a fuel holding part for forming a coolant passage along the longitudinal direction between the channel box and the fuel rods and between the fuel rods in a channel box having a rectangular cross section. In the case where an inclined flow tab for directing the flow of the coolant toward the fuel rod side is provided at least at the edge of the support band on the downstream side of the coolant flow, the surface of the flow tab on the upstream side of the coolant flows toward the coolant flow. It is characterized in that it has an uneven surface or a surface with protrusions to disperse.

According to a third aspect of the present invention, a support frame having a square frame shape for supporting a bundle of a plurality of fuel rods from the outer peripheral side, and the fuel rods connected to the inside of the support band are held in a grid-like arrangement in a separated manner. And a fuel holding part for forming a coolant passage along the longitudinal direction between the channel box and the fuel rods and between the fuel rods in a channel box having a rectangular cross section. In the case where an inclined flow tab for directing the flow of the coolant toward the fuel rod side is provided at least on the edge of the support band on the downstream side of the coolant flow, at the tip position of the surface of the flow tab on the coolant flow upstream side, It is characterized in that an edge portion is provided to prevent a straight flow of the coolant flow.

According to a fourth aspect of the present invention, a support frame having a rectangular frame shape for supporting a bundle of a plurality of fuel rods from the outer peripheral side, and the fuel rods connected to each other inside the support band are held in a lattice-like arrangement. And a fuel holding part for forming a coolant passage along the longitudinal direction between the channel box and the fuel rods and between the fuel rods in a channel box having a rectangular cross section. A flow tab is formed between the support band and the fuel rod, wherein at least an edge portion of the support band on the downstream side of the coolant flow is provided with an inclined flow tab for directing the flow of the coolant toward the fuel rod. It is characterized in that it has a shape that covers substantially the entire surface of the gap channel.

According to a fifth aspect of the present invention, a square frame-shaped support band for supporting a bundle of a plurality of fuel rods from the outer peripheral side, and the fuel rods connected to the inside of the support band are held in a grid-like arrangement with a space therebetween. And a fuel holding part for forming a coolant passage along the longitudinal direction between the channel box and the fuel rods and between the fuel rods in a channel box having a rectangular cross section. In the case where an inclined flow tab for directing the flow of the coolant toward the fuel rod is provided at least at the edge of the support band on the downstream side of the flow of the coolant, the flow tab has a triangular cross section protruding toward the inner surface side of the support band. The shape is characterized in that the cross-section gradually expands along the flow direction of the coolant.

According to a sixth aspect of the present invention, a support frame having a rectangular frame shape for supporting a bundle of a plurality of fuel rods from the outer peripheral side, and the fuel rods that are continuously provided inside the support band are held in a lattice-like arrangement with a space therebetween. And a fuel holding part for forming a coolant passage along the longitudinal direction between the channel box and the fuel rods and between the fuel rods in a channel box having a rectangular cross section. A flow tab that directs the flow of the coolant toward the fuel rod is formed at least at the edge of the support band on the downstream side of the coolant flow, and the flow tab forming portion of the support band is cooled by receiving the flow of the coolant. The material flow upstream end is a movable flow skirt that moves toward the channel box.

According to a seventh aspect of the present invention, in the fuel spacer according to the sixth aspect, the flow skirt portion of the support band is pivoted to the fuel rod holding portion located at the corner portion of the fuel assembly via the hinge portion. It is characterized by being supported as much as possible.

According to an eighth aspect of the present invention, in the fuel spacer according to the sixth aspect, the support bands are arranged at the corner band portions arranged at the corners of the fuel assembly and the side portions of the fuel assembly. It is characterized in that it is divided into a side band portion, a flow tab is formed in the side band portion, and the side band portion is supported by the corner band portion so as to be rotatable or movable in parallel.

According to a ninth aspect of the present invention, a square frame-shaped support band for supporting a bundle of a plurality of fuel rods from the outer peripheral side, and the fuel rods which are continuously provided inside the support band and are held in a grid-like arrangement in a separated manner. And a fuel holding part for forming a coolant passage along the longitudinal direction between the channel box and the fuel rods and between the fuel rods in a channel box having a rectangular cross section. A flow tab that directs the flow of the coolant toward the fuel rod side is formed at least at the edge of the support band on the downstream side of the coolant flow, the support band being provided at a corner of the fuel assembly. It is divided into a band portion and a side band portion arranged on the side portion of the fuel assembly, the side band portion is made of an elastic material, and the downstream end of the coolant flow is formed into a channel box. It urges the scan side, and is characterized in that to form a guide hole for coolant circulation in the sideband portion.

According to a tenth aspect of the present invention, a plurality of fuel rods arranged in a grid, a tie plate for fixing and holding both ends of each fuel rod, and a channel box having a rectangular cross section for covering these fuel rods and each tie plate. And a plurality of fuel spacers arranged in the channel box at intervals along the longitudinal direction to form a coolant passage along the longitudinal direction between the fuel rods and between the fuel rods. In the fuel assembly, the fuel spacers other than those located on the most downstream side of the coolant passage are the fuel spacers according to any one of claims 1 to 9.

The eleventh aspect of the present invention is directed to a plurality of fuel rods arranged in a lattice, tie plates for fixing and holding both ends of each fuel rod, and a channel box having a rectangular cross section for covering these fuel rods and each tie plate. And a plurality of fuel spacers arranged in the channel box at intervals along the longitudinal direction to form a coolant passage along the longitudinal direction between the fuel rods and between the fuel rods. The fuel spacer according to any one of claims 1 to 9, wherein in the fuel assembly, the fuel spacer arranged in a region on a downstream side of a coolant flow from a central position in a longitudinal direction of a fuel heating portion of the fuel rod is used. Characterize.

According to a twelfth aspect of the present invention, a plurality of fuel rods arranged in a grid, a tie plate for fixing and holding both ends of each fuel rod, and a channel box having a rectangular cross section for covering these fuel rods and each tie plate. And a plurality of fuel spacers arranged in the channel box at intervals along the longitudinal direction to form a coolant passage along the longitudinal direction between the fuel rods and between the fuel rods. The fuel spacer according to any one of claims 1 to 9, characterized in that, in the fuel assembly, the fuel spacer arranged in a region of the fuel heat generating portion of the fuel rod on the downstream side of the coolant flow is ⅔. To do.

[0045]

According to the first aspect of the present invention, a cross section with an edge is provided in which all or part of the flow tab suppresses the inflow of the coolant into the surface on the downstream side of the coolant flow and expands the negative pressure generated on the same surface. By having a shape, the edge prevents the entrainment of droplets from the side of the flow tab. Therefore, the negative pressure on the surface of the flow tab on the downstream side of the coolant flow can be increased, and by widening the negative pressure region, the flow from between the channel box and the flow tab toward the downstream surface of the flow tab can be strengthened.

According to the second aspect of the present invention, the surface of the flow tab on the upstream side of the coolant flow is made into the uneven surface or the surface with projections for dispersing the coolant flow, thereby preventing the trapped liquid droplet from going straight. The amount of dispersion suitable for the fuel rod can be increased. Therefore, the cooling efficiency becomes better than that of the conventional flow tub.

According to the third aspect of the present invention, the edge portion for preventing the straight flow of the coolant flow is provided at the tip position of the surface of the flow tab on the upstream side of the coolant flow. It is possible to improve the cooling efficiency by increasing the amount of dispersion toward the fuel rods by preventing the straight movement of the fuel cells.

According to the fourth aspect of the present invention, the flow tab has a shape that covers substantially the entire surface of the gap flow path formed between the support band and the fuel rod, so that the projected area of the flow tab along the longitudinal direction of the fuel rod. Can be increased to prevent mere passage of the coolant flowing in this portion, thus improving the cooling efficiency. That is, the coolant flowing in the gap between the outermost fuel rod and the spacer band is biased toward the inner side of the fuel, and the coolant in the fuel gap is more and more effectively biased to the inside of the fuel. The thermal margin can be improved.

According to the invention of claim 5, the flow tab is
Compared with the conventional flow tab, the direction of the droplets in the steam flowing in the flow path is compared to the conventional flow tab by adopting a triangular cross-section protruding to the inner surface side of the support band and gradually increasing the cross-section along the flow direction of the coolant. Then, it can be smoothly directed to the fuel rod surface side. As a result, the liquid film flow rate on the surface of the fuel rod is increased, and the resistance of the outermost peripheral flow path is reduced due to the flow tab having a triangular cross section. Can be increased to increase the liquid phase supplied to the fuel rod surface.

According to the sixth aspect of the invention, the flow tab forming portion of the support band is a movable flow skirt portion in which the coolant flow upstream end moves to the channel box side in response to the flow of the coolant. Then, the flow skirt portion is moved to the channel box side by the upward lifting force of the coolant from the lower side. As a result, the liquid phase on the inner wall of the channel box is separated, and the separated liquid phase can improve the cooling efficiency of the fuel rod.
In the state where the coolant does not flow, the lifting force does not act, so that the flow skirt portion is separated from the channel box and is held as a support band, so that there is no hindrance to the assembly and disassembly of the fuel assembly.

According to the invention of claim 7, the flow skirt portion of the support band is rotatably supported by the fuel rod holding portion located at the corner portion of the fuel assembly through the hinge portion. With such a configuration, the smooth operation can be performed by the rotation of the flow skirt, and the liquid phase separation action can be efficiently obtained.

According to the invention of claim 8, the support band is
It is divided into a corner band portion arranged at a corner portion of the fuel assembly and a side band portion arranged on a side portion of the fuel assembly, and a flow tab is formed on this side band portion, and this side band portion is formed. By supporting the corner band portion so as to be rotatable or movable in parallel, the liquid phase peeling action can be obtained with the same simple structure as the invention of the seventh aspect. In addition,
When the entire flow skirt is configured to move to the channel box side, the liquid phase separation action is performed more reliably.

According to the invention of claim 9, the support band is
The corner band of the fuel assembly is divided into a corner band and a side band of the fuel assembly, and the side band is made of an elastic material. By urging the side end (upper end) toward the channel box and forming a guide hole for coolant circulation in this side band, the upper end of the side band is always in contact with the channel box. Similarly to the structure having the flow skirt, the cooling efficiency of the fuel rod can be improved by the liquid phase separation of the inner wall of the channel box. In the case of the present invention, since the upper end portion of the side band portion is in contact with the channel box regardless of the flow of the coolant, it requires a little labor for mounting and the like as compared with the configuration having the flow skirt portion. In short, the liquid phase separation action can be performed more reliably regardless of the coolant flow rate.

According to the tenth aspect of the present invention, the fuel spacer according to any one of the first to ninth aspects is applied as a fuel spacer excluding the fuel spacer located on the most downstream side of the coolant flow path, whereby the core is An effective cooling effect can be obtained as a whole.

According to the eleventh aspect of the present invention, the fuel spacer according to any one of the first to ninth aspects is arranged in the region downstream of the coolant flow from the central position in the longitudinal direction of the fuel heating portion of the fuel rod. Thus, an effective cooling effect can be obtained in the upper part of the core where gas-liquid separation is severe.

According to the twelfth aspect of the present invention, the installation region of the fuel spacer according to any one of the first to ninth aspects is set in the region ⅔ on the downstream side of the coolant flow of the fuel heating portion of the fuel rod. By doing so, a more effective cooling effect at a necessary portion can be obtained.

[0057]

EXAMPLES Examples of the fuel spacer and the fuel assembly according to the present invention will be described below with reference to FIGS. The overall structure of the fuel spacers of the following embodiments is substantially the same as that shown in FIG. 45, so refer to FIG. 45 for the description of the embodiments, and regarding the structure of the fuel assembly to which the fuel spacer is applied, Since the configuration is similar to the conventional configuration shown in FIG. 44, FIG. 44 is also used in the description of the following embodiment.

Embodiment 1 (FIGS. 1 to 5) This embodiment relates to a fuel spacer. FIG.
Is a perspective view showing the basic configuration of the present embodiment, and FIG. 2 is an explanatory view showing the operation. 3, 4, and 5 are perspective views showing modified examples.

As shown in FIGS. 1, 44 and 45,
The fuel spacer 7 of this embodiment includes a support frame 11 having a rectangular frame shape for supporting a bundle of a plurality of fuel rods 3 from the outer peripheral side, and the fuel rods 3 connected to the inside of the support band 11 and each fuel rod 3 is, for example, 8 ×.
8 and the like, circular cells 16 as fuel holding portions which are held in a grid-like arrangement in a spaced-apart manner are provided, and between the channel boxes 2 and the fuel rods 3 and between the fuel rods 3 in the channel box 2 having a rectangular cross section. A coolant passage is formed along the longitudinal direction.

At the edge of the support band 11 on the downstream side of the coolant flow (upper edge), the flow tab 1 inclined toward the fuel rod 3 side is provided.
2 are integrally provided so that the flow of the coolant from the lower side to the upper side in the figure is directed to the fuel rod 3 side. Edges 17 are integrally erected on both side edges of the surface (upper surface) 12a of the flow tab 12 on the downstream side of the coolant flow, whereby the entire flow tab 12 has an edge (a U-shaped cross section).

When the fuel assembly 1 is constructed by using the fuel spacer 7 having such a flow tab 12, as shown in FIG. 2, the flow of the coolant upward in the channel box 2 (arrow d). Is directed to the fuel rod 3 side along the inclination of the flow tab 12, and the downstream surface 12a of the flow tab 12 becomes the negative pressure region 15 due to the uneven flow, but the negative pressure is applied by the edges 17 rising on both side edges of the flow tab 12. Since the area 15 is shielded from both sides outwardly, the coolant will rise outside each edge 17 (arrow e),
The inflow into the negative pressure region 15 from the direction intersecting the coolant flow direction is significantly suppressed as compared with the case of the conventional flat plate-shaped flow tab (see the arrow in FIG. 53).

Therefore, according to the fuel spacer 7 of the present embodiment, the surface 12 of the flow tab 12 on the downstream side of the coolant flow.
Since the negative pressure area of the flow tab 12 is expanded by suppressing the entrainment in a, the channel box 2 and the flow tab 1
It is possible to strengthen the flow of the coolant from between the fuel cell 2 and the fuel rod 3 toward the fuel rod 3 side, whereby many droplets in the vicinity of the inner surface of the channel box 2 can be attached to the fuel rod 3 side, and the thermal margin of the outermost peripheral fuel rod is increased. Can be improved as compared with the conventional one.

In the modification of the present embodiment shown in FIG. 3, the flow tab 12 is bent in a V-shaped cross section, and the surface 12a on the downstream side of the coolant flow is formed on both outer sides by edges 17 on both sides rising in an inclined shape. It is configured to be shielded from. In this example, the surface 12a of the flow tab 12 on the downstream side of the coolant flow.
Is gradually narrowed toward the tip side, and the rising height of the edge 17 is gradually increased toward the tip side.

In the modification of this embodiment shown in FIG. 4, the flow tab 12 is curved in a U-shaped cross section, and the surface 12a on the downstream side of the coolant flow is shielded from both outer sides by the curved edges 17. It is composed.

With the configuration of the modified examples shown in FIGS. 3 and 4, as in the example shown in FIG.
By the edges 17 rising on both side edge portions of 2, the entrainment of the coolant flow of the flow tab 12 into the downstream surface 12a can be suppressed.

In the modification of this embodiment shown in FIG. 5, contrary to the example of FIG. 1, edges 17 are provided so as to project downward at both side edges of the surface (lower surface) 12b of the flow tab 12 on the upstream side of the coolant flow. As a result, the entire flow tab 12 has an edge (a U-shaped cross section).

In the modified structure shown in FIG. 5, the flow rate of the coolant flowing upward from both sides of the lower surface 12b of the flow tab 12 can be suppressed, and as a result, the flow tab 12 has the same flow rate as in each of the above-described examples. Entrainment of the coolant flow into the downstream surface 12a can be suppressed.

In the above example, the entire portion of the flow tab 12 has a sectional shape with an edge which suppresses the inflow of the coolant into the surface 12a on the downstream side of the coolant and expands the negative pressure generated on the same. A part of the flow tab 12 may have a cross-sectional shape with an edge.

Embodiment 2 (FIGS. 6 to 9) In this embodiment, the surface (lower surface) 1 on the upstream side of the coolant flow of the flow tab 12 provided on the support band 11 of the fuel spacer 7 is shown.
2b is an uneven surface or a surface with protrusions for dispersing the coolant flow, or has a tip edge. FIG. 6 is a bottom view showing the structure in the case of using an uneven surface or a surface with protrusions, and FIG. 7 is a sectional view taken along the line AA of FIG. FIG. 8 is a bottom view showing a configuration with a tip edge, and FIG. 9 is a B- of FIG.
It is a B sectional view.

In the fuel spacer 7 of the embodiment shown in FIG. 6 and FIG. 7, the surface (lower surface) 12b of the flow tab 12 on the upstream side of the coolant flow is directed toward the fuel rod 3 which is close to the center position of the flow tab 12. Inclined V-shaped convex portion 18
Are formed at intervals toward the tip side of the flow tab 12. As a result, the lower surface of the flow tab 12 has a plurality of wrinkled uneven surfaces.

In the fuel assembly 1 using the fuel spacer 7 having the flow tab 12 having such a configuration, as shown in FIG. 7, the coolant (arrow f1) rising along the inside of the support band 11 of the fuel spacer 7 is used. 8) when the flow is lopsided on the upstream surface 12b which is the lower surface of the flow tab 12, as shown in FIG. 8, it becomes a dispersed flow directed to each fuel rod 3 side by the substantially V-shaped convex portion 18 of the flow tab 12 (arrow f2), the rectilinear flow (flow to the left in FIG. 6) directed toward the tip side of the flow tab 12 that escapes between the fuel rods 3 decreases.

Therefore, according to the present embodiment, most of the liquid droplets captured by the flow tab 12 form a dispersed flow toward the fuel rod 3 side, so that the fuel cooling efficiency is better than that of the conventional fuel flow tab configuration. Will be things.

In the configuration examples shown in FIGS. 6 and 7, the shape of the convex portion 18 is substantially V-shaped, and the number thereof is three. However, the shape of the convex portion 18 and the shape of the uneven surface resulting therefrom Also, the number and the like are not limited to those shown in the drawings, and various modifications are possible. For example, a plurality of plate-shaped protrusions may be used.

In the embodiment shown in FIGS. 8 and 9, an edge 19 for preventing a rectilinear flow is provided downwardly at the tip of the surface 12b of the flow tab 12 on the upstream side of the coolant flow.

With this structure as well, similarly to the above, when the coolant (arrow f1 in FIG. 9) rising along the inside of the support band 11 drifts on the upstream surface 12b of the flow tab 12, the flow tab 12 moves. By the edge 19 at the tip, a dispersed flow is directed toward each fuel rod 3 side (arrow f3 in FIG. 8), and a straight flow toward the tip end side of the flow tab 12 that escapes between the fuel rods 3 can be reduced.

The uneven flow of the coolant due to the convex portions 18 and the edges 19 has a component force in the direction away from the flow tab 12, so that the coolant flows around the downstream surface (upper surface) 12a of the flow tab 12. Since it also contributes to the reduction of the above, there is also an effect of supplementing the expansion of the negative pressure region of the first embodiment. Therefore, if the configuration of the second embodiment and the configuration of the first embodiment are used in combination, it becomes more effective in cooling the fuel rod.

Embodiment 3 (FIGS. 10 to 13) In the fuel spacer 7 of this embodiment, the flow tab 12 is shaped so as to cover substantially the entire surface of the gap flow passage formed between the support band 11 and the fuel rod 3. It is a thing. 10, 11 and 12 are perspective views showing the configurations of flow tabs 12 having different shapes, and FIGS. 13 (A) and 13 (B) are explanatory views showing the operation.

In the present embodiment, in the fuel spacer 7 shown in FIG. 10, the flow tab 12 is inclined toward the inner peripheral side from the rising portion 12c which is substantially flush with the edge of the support band 11 on the downstream side of the coolant flow. It has a trapezoidal shape and is bent in a rectangular shape, and the widthwise dimension is enlarged as compared with the conventional configuration (see FIGS. 55 and 56). Further, the flow tab 12 shown in FIG. 11 has an enlarged projecting length dimension as compared with the conventional configuration. Further, the flow tab 12 shown in FIG.
In comparison with the conventional configuration, the widthwise dimension and the protruding length dimension are enlarged, and both side edge portions are curved and the tip portion is narrowed.

As shown in FIG. 13 (A), the flow tab 12 having the expanded width or protruding length as described above
The gap passage 20 formed between the support band 11 and the fuel rod 3 is covered with substantially the entire surface. Therefore, according to the fuel spacer 7 of the present embodiment, FIG.
As shown in FIG. 5, of the coolant that rises in the gap passage 20 formed between the support band 11 and the fuel rod 3, the flow (arrow g) that rises through the side of the flow tab 12 is As compared with the case of the conventional example shown in FIG. 55, the flow is reduced, and the flow (arrow h) that drifts toward the fuel rod 3 side increases.

Therefore, according to this embodiment, the coolant flowing in the gap portion 20 between the outermost fuel rod 3 and the support band 12 is made to flow more and more effectively to the fuel rod side, so that the fuel The thermal margin can be improved.

Embodiment 4 (FIGS. 14 to 29) The fuel spacer 7 of this embodiment has a triangular cross section in which the flow tab 12 projects toward the inner surface of the support band 11, and has a cross section gradually extending in the direction of the flow of the coolant. Is a shape that expands. 14 to 17 show a basic configuration example, and FIG.
21 is a first modification, FIGS. 22 to 25 are second modifications,
26 to 29 each show a third modification.

First, a basic configuration example will be described with reference to FIGS. 14 is a perspective view of the flow tab 12 portion of the fuel spacer 7, FIG. 15 is a front view thereof, FIG. 16 is a side sectional view thereof, and FIG. 17 is a plan view thereof.

In this fuel spacer 7, the support band 11
The flow tab 12 protruding to the inner surface side of is formed by a plate material bent in a triangular pyramid shape. This flow tab 12
Rises from a substantially middle position in the coolant flow direction of the support band 11 and extends to the coolant flow downstream side end (upper end) of the support band 11 and is gradually cross-sectioned along the coolant flow direction (upper). Has a shape that linearly expands.

According to the fuel spacer 7 having such a triangular flow tab 12 having a convex cross section on the inner surface of the support band, the cooling which rises in the gap flow passage 20 formed between the support band 11 and the fuel rod 3. The material (droplets in the steam) can be smoothly directed to the surface side of the fuel rod 3 as compared with the conventional single-plate flow tab. Therefore, the flow rate of the liquid film on the surface of the fuel rod 3 can be increased, and the structure of the triangular cross-section further reduces the resistance of the gap channel 20 at the outermost periphery and allows the passage in the channel. Since the passing amount of the accompanying liquid phase can also be increased by increasing the flow rate of the vapor, the liquid phase supplied to the surface of the fuel rod 3 can be increased.

Next, a first modification will be described with reference to FIGS. 18 is a perspective view of the flow tab 12 portion of the fuel spacer 7, FIG. 19 is a front view thereof, FIG. 20 is a side sectional view thereof, and FIG. 21 is a plan view thereof.

In this fuel spacer 7 as well, the flow tab 12 projecting to the inner surface side of the support band 11 is made of a plate material bent in the shape of a triangular pyramid, and the flow tab 12 is located at a substantially intermediate position in the coolant flow direction of the support band 11. It rises and has a shape in which the cross section gradually expands linearly along the direction (upward) of the flow of the coolant. This point is substantially the same as the basic configuration example, but in this example, the flow tab 12 further extends to a position above the coolant flow downstream end (upper end) of the support band 11. The cross section of the protruding portion 12d of the flow tab 12 above the support band 11 is the same as the cross section of the upper end portion of the main body portion 12e which is the non-projecting portion.

According to this structure, in addition to the same operational effects as the basic structure example described above, the flow tab 12 is provided with the protruding portion 12d above the support band 11, so that the inside of the gap flow path 20 is improved. The coolant that has risen to the upper end of the support band 11 can be smoothly flowed upward without causing flow turbulence.

Next, a second modification will be described with reference to FIGS. 22 is a perspective view of the flow tab 12 portion of the fuel spacer 7, FIG. 23 is a front view thereof, FIG. 24 is a side sectional view thereof, and FIG. 25 is a plan view thereof.

In this fuel spacer 7 as well, the flow tab 12 projecting to the inner surface side of the support band 11 is made of a plate material bent in a triangular pyramid shape, and the flow tab 12 is located at a substantially intermediate position of the support band 11 in the coolant flow direction. It is substantially the same as the basic configuration example in that it has a shape that rises and the cross-section gradually increases along the direction (upper direction) of the coolant flow to the end (upper end) on the coolant flow downstream side of the support band 11. Is. However, in this example, the enlarged sectional shape of the flow tab 12 facing upward is curved in a streamlined shape.

According to this structure, the flow tab 12
Is curved in a streamlined shape, a smoother drifting action of the coolant can be obtained as compared with the basic configuration example.

Next, a third modification will be described with reference to FIGS. 26 is a perspective view of the flow tab 12 portion of the fuel spacer 7, FIG. 27 is a front view thereof, FIG. 28 is a side sectional view thereof, and FIG. 29 is a plan view thereof.

This fuel spacer 7 is the same as the second modification in the third modification.
The element of the modified example is added. That is, the flow tab 12 projecting to the inner surface side of the support band 11 is configured such that the cross-section gradually expands in the coolant flow direction by the streamlined curved plate material bent in a triangular pyramid shape. The coolant flow extends from the downstream end (upper end) to an upper position. The cross section of the protruding portion 12d of the flow tab 12 above the support band 11 is the same as the cross section of the upper end portion of the main body portion 12e which is the non-projecting portion.

According to this structure, the flow tab 12
Is curved in a streamlined shape, a smoother drifting action of the coolant can be obtained as compared with the basic configuration example described above, and the flow tab 12 is provided with the protruding portion 12d above the support band 11. In this way, both the effect that the coolant that has risen to the upper end portion of the support band 11 in the gap flow passage 20 can be smoothly flowed upward without causing flow turbulence is exhibited.

Fifth Embodiment (FIGS. 30 to 33) The fuel spacer 7 of the present embodiment to the seventh embodiment is a movable type in which the flow tab forming portion of the support band 11 is moved to the channel box side by the flow of the coolant. This is the flow skirt part. FIG. 30 is a perspective view showing the overall structure of the present embodiment, FIGS. 31 and 32 are explanatory views showing the closed and open states of the flow skirt, respectively, and FIG. 33 is the separation of the liquid phase on the inner surface of the channel box 2. It is an explanatory view showing the situation of.

As shown in FIG. 30, the fuel spacer 7 of this embodiment is of a cell type, and has a plurality of circular shapes (16 pieces) serving as fuel holding portions for holding the fuel rods 3 in a 4 × 4 lattice arrangement, for example.
Cells 21 adjacent to each other in the vertical and horizontal directions are welded and fixed to each other. The support band 11 is configured as a side band type located in the fuel rod holding cell 21 located on the side of the fuel assembly 1, and is composed of four elements corresponding to four sides.

Each element of the support band 11 serves as a flow skirt 22. Each of the flow skirts 22 has a rectangular main body 23, and a plurality (three) of flow tabs 12 integrally projecting at a downstream end edge (upper edge) of the main body 23 on the coolant flow side. , Body 23
And a skirt portion 24 that is integrally connected to the upstream edge (lower edge) of the coolant flow and is inclined toward the outer peripheral side.

Further, fulcrum pins 25 are provided on upper portions of both lateral ends of the main body portion 23, and the fulcrum pins 25 are rotatably supported by a pair of cells 21a located at the corners via hinges 26. Has been done. A protruding guide 27 having the same shape as the hinge 26 is provided below the cell 21a located at the corner. This guide 27 has a guide function for inserting the fuel bundle into the channel box 2,
It has a guide function for centering the fuel bundle in the channel box 2.

According to the fuel spacer 7 of the present embodiment having such a structure, in the situation where the coolant does not flow, FIG.
As shown in FIG. 1, the flow skirt 22 is held vertically along the cell 21.

On the other hand, when the coolant flows from the lower side to the upper side of the fuel assembly 1, as shown in FIG.
The coolant hits the skirt portion 24 at the lower end of 2 to act as a lifting force, and the component force at that time generates a turning force in which the lower end faces the outer peripheral side about the hinge 26 portion in the flow skirt 22. The turning force is a moment due to the product of the distance from the center of rotation and the fluid force generated at that location, but by setting the center of rotation (O in FIG. 33) above the vertical center, the flow skirt 22 A turning force can be applied so that the lower side expands.

As the lower side of the flow skirt 22 is rotated so as to expand, the skirt portion 24 comes into contact with the inner surface of the channel box 2 as shown in FIG. The phases can be forced to exfoliate. The flow of the separated liquid phase, after flowing along the flow skirt, becomes a liquid phase jet (arrow i), and the liquid phase jet heads toward the fuel rod 3, thereby contributing to the cooling of the fuel rod 3. You can

When the coolant does not flow, the lifting force on the flow skirt 22 ceases to act, so the flow skirt 22 separates from the channel box 2 and is held as a support band. It does not hinder assembly and disassembly.

According to this embodiment, the flow skirt 22 of the support band 11 is rotatably supported by the cells 21a located at the corners of the fuel assembly 1 via the hinges 26. A smooth operation can be performed by the rotation of the flow skirt 22, and the liquid phase separation action over a wide range can be efficiently obtained.

Embodiment 6 (FIGS. 34 to 37) In the fuel spacer 7 of this embodiment, the support band 11 covers the fuel rods 3 located at the corners of the fuel assembly 1, the corner band portion 28, and the fuel assembly. It is divided into a side band portion 29 that covers the fuel rods 3 located on the sides of the body 1, and the side band portion 29 is rotatable as a flow skirt. 34 is a perspective view showing the overall configuration of this embodiment, and FIG.
And FIG. 36 are explanatory diagrams showing a closed state and an opened state of the flow skirt portion, respectively, and FIG. 37 is an explanatory diagram showing a state of separation of the liquid phase on the inner surface of the channel box 2.

As shown in FIG. 34, the fuel spacer 7 of this embodiment is also of a cell type, and has a plurality of circular shapes (16 pieces) as fuel holding portions for holding the fuel rods 3 in a 4 × 4 lattice arrangement, for example.
Cells 21 adjacent to each other in the vertical and horizontal directions are welded and fixed to each other. The support band 11 includes four corner band portions 28 that cover the fuel rods 3 located at the corners of the fuel assembly 1 and four side bands that cover the fuel rods 3 located on the sides of the fuel assembly 1. It is divided into a part 29 and a part 29. Each corner band portion 28 is fixed to the cell 21a at the corner position. Each side band portion 29 is a flow skirt.

The side band portion 29 as each flow skirt has a rectangular main body portion 30 and the main body portion 23.
One flow tab 12 integrally provided on the downstream edge (upper edge) of the coolant flow and the outer peripheral side integrally connected to the upstream edge (lower edge) of the coolant flow on the main body 30. And a pair of support tabs 32 and 33 provided on the upper and lower portions of both lateral ends of the main body 30. The support tabs 32 and 33 are formed on the corner band portion 28.
It engages with a pair of upper and lower cutouts 34 and 35 formed at the end of the fuel spacer 7 and is slidable within a certain range in the inner and outer directions of the fuel spacer 7. Then, each of the support tabs 32, 33
Among them, the length of the lower support tab 33 is set to be longer than that of the upper support tab 32, so that the lower end side of the side band portion 29 as the flow skirt can be slid larger than the upper end side.

According to the fuel spacer 7 of this embodiment having such a structure, in a situation where the coolant does not flow, as in the case of the above-mentioned Embodiment 5, as shown in FIG. Held vertically.

On the other hand, when the coolant flows from the lower side to the upper side of the fuel assembly 1, as shown in FIG.
The coolant hits the skirt portion 31 at the lower end of 9 to act as a lifting force, and the component force at that time generates a force that directs the lower end of the side band portion 29 toward the outer peripheral side. Slide to the outside (right side in the figure). In this case, since the length of the lower support tab 33 is set to be longer than that of the upper support tab 32, the lower support tab 3 is slid for a certain distance and stopped, and thus the lower support tab 3 is also stopped.
Since the third side slides, the side band portion 29 rotates with the vicinity of the locking position of the upper support tab 32 (position of point O in FIG. 33) as a fulcrum.

When the lower side band portion 29 is rotated so as to expand, the skirt portion 31 contacts the inner surface of the channel box 2 and rises along the inner surface of the channel box 2, as shown in FIG. The liquid phase can be forcibly peeled off. The separated liquid phase flow becomes a liquid phase jet flow (arrow i) after flowing along the side band portion 29, as in the fifth embodiment, and the liquid phase jet flow is directed to the fuel rod 3, Can contribute to the cooling of the fuel rods 3.

Even in this embodiment, when the coolant does not flow, the lifting force to the side band portion 29 does not act, so the side band portion 29 is separated from the channel box 2 and is held as a support band. Therefore, it does not hinder the assembly and disassembly of the fuel assembly.

Also according to this embodiment, the side band portion 29 of the support band 11 is rotatably supported by the cells 21a located at the corners of the fuel assembly 1 via the hinges 26, and has a simple structure. A smooth operation can be performed by the rotation of the side band portion 29, and a liquid phase separation action over a wide range can be efficiently obtained.

Embodiment 7 (FIGS. 38 to 41) In this embodiment, as in the case of Embodiment 6, the corner band portion 28 for covering the fuel rod 3 located at the corner of the fuel assembly 1 with the support band 11 is formed. And a side band portion 29 that covers the fuel rods 3 located on the sides of the fuel assembly 1, and this side band portion 29 is used as a flow skirt. The part 29 can be laterally moved by modifying a part of the configuration. 38 is a perspective view showing the overall configuration of this embodiment, FIGS. 39 and 40 are explanatory views showing the flow skirt portion in a closed state and an opened state, respectively, and FIG. 41 is a liquid phase separation on the inner surface of the channel box 2. It is an explanatory view showing the situation of.

In this embodiment, as shown in FIG. 38, there is no skirt portion at the lower end of the side band portion 29 as a flow skirt, and the upper portion of the flow tab 12 inclines inward of the fuel spacer 7 to raise the cooling. It is designed to receive the force of the flow of wood. Also, the support tabs 3 above and below the side band portion 29 for supporting the corner band portion 28.
No difference in length is provided between 2 and 33. On the other hand, the pair of upper and lower cutouts 34, 35 formed at the end of the corner band portion 28 are curved guide grooves that gradually increase toward the outside of the fuel spacer 7.

In this embodiment having such a structure, as shown in FIGS. 39 and 40, when the coolant flows from below the fuel spacer 7, the force due to the rising coolant flow acts on the flow tab 12. The fluid force that lifts the side band portion 29 upward acts. Due to this force, the side band portion 29 moves upward, and the notch portion 3 as a guide groove is formed.
Guided outward along 4,35 and move. When the side band portion 29 is moved outward, the entire side band portion 29 contacts the inner surface of the channel box 2.

As a result, as shown in FIG. 41, the liquid phase on the inner surface of the channel box is separated by the flow tab 12 of the side band portion 29 which is in contact with the channel box 2. The peeled liquid phase improves the cooling efficiency of the fuel rods in the same manner as described above.

Embodiment 8 (FIGS. 42 and 43) This embodiment is similar to Embodiments 6 and 7 in that the support band 1 is used.
1 is divided into a corner band portion 28 that covers the fuel rods 3 located at the corners of the fuel assembly 1, and a side band portion 29 that covers the fuel rods 3 located at the sides of the fuel assembly 1. However, the side band portion 29 is fixedly configured. 42 is a perspective view showing the overall structure of this embodiment, and FIG.
FIG. 4 is an explanatory diagram showing a state of liquid phase separation on the inner surface of the channel box 2.

In this embodiment, as shown in FIG. 42 and FIG. 43, the end of the side band portion 29 on the downstream side of the coolant is made of an elastic material urged to the outside, and the upper portion thereof is cooled as a guide hole. A material distribution hole 36 and a semi-roofed flow restricting plate 37 that covers the cooling material distribution hole 36 are provided. The flow tab 12 is inclined toward the inside of the fuel spacer 7, as in the seventh embodiment. The upper end of the side band portion 29 is in pressure contact with the inner surface of the channel box 2.

According to this embodiment, the side band portion 29 of the support band 11 is made of an elastic material, and the downstream end (upper end) of the coolant flow is urged toward the channel box 2 side. By forming the coolant circulation hole 36 as a guide hole in the side band portion 29, the upper end portion of the side band portion 29 is always in contact with the channel box 2 and is in a tilted state, and the coolant flows upward through the coolant circulation hole 36. Will be able to pass through. Then, the flow tab 12 causes the flow to be biased toward the fuel rod side.

Therefore, also in this embodiment, the cooling efficiency of the fuel rods can be improved by the liquid phase separation of the inner wall of the channel box 2 as in the structure having the flow skirt portion. In the case of the present embodiment, the upper end of the side band portion 29 is in contact with the channel box 2 regardless of the flow of the coolant, so that the mounting or the like may be slightly different from that of the structure having the flow skirt portion. However, the action of liquid phase separation can be performed more reliably regardless of the coolant flow rate.

In each of the above embodiments, the round cell type spacer is described, but it may be a cell type having another shape, and may be applied to a spacer of another type (for example, grid type).

Further, in each of the above embodiments, the fuel spacer used in the 4 × 4 lattice arrangement is shown, but it is 7 × 7,8 ×.
Needless to say, the present invention can be appropriately applied to other fuel spacers in a lattice arrangement such as 8.

Furthermore, it is also possible to combine the configurations of the above-described first to eighth embodiments and implement them as various modifications.

Example 9 This example relates to the fuel assembly shown in FIG. In this embodiment, a plurality of fuel rods 3 arranged in a grid pattern are used.
And tie plates 8 and 9 for fixing and holding both ends of each fuel rod 3, and these fuel rods 3 and each tie plate 8 and 9.
A box box 2 having a quadrangular cross section for covering the pipes, and cooling along the longitudinal direction between the channel box 2 and the fuel rods 3 arranged in the channel box 2 at intervals along the longitudinal direction. In a fuel assembly including a plurality of fuel spacers 7 forming a material flow path,
The fuel spacer 3 excluding the one located on the most downstream side of the coolant flow path is applied as any one of the first to eighth embodiments or a fuel spacer combining these.

According to this structure, the fuel spacers 7 other than those located at the most downstream side of the coolant flow channel effectively perform the coolant drift function as described above. It is possible to obtain a good cooling effect.

[ Embodiment 10 ] This embodiment is substantially the same as Embodiment 9 except that in the fuel assembly shown in FIG. 44, the portion from the longitudinal center of the fuel heat generating portion of the fuel rod 3 to the coolant flow downstream side. The fuel spacer 7 arranged in the region is the fuel spacer of any one of the first to eighth embodiments or a combination thereof.

According to the present embodiment as described above, by disposing the fuel spacers of Embodiments 1 to 8 in the region on the downstream side of the coolant flow from the center position in the longitudinal direction of the fuel heating portion of the fuel rod 3, An effective cooling effect can be obtained in the upper part of the core where liquid separation is severe.

[ Embodiment 11 ] This embodiment is substantially the same as the above-mentioned Embodiment 9, except that in the fuel assembly shown in FIG. Fuel spacer 7 to be placed
Is used as the fuel spacer of any one of the first to eighth embodiments or a composite thereof.

According to this embodiment as described above, the fuel spacers of Embodiments 1 to 8 are arranged in the region of the fuel heat generating portion of the fuel rod 3 on the downstream side 2/3 of the coolant flow side, so that the fuel spacer can be formed at a necessary portion. A more effective cooling effect can be obtained.

[0128]

As described above in detail, according to the present invention, it is possible to efficiently direct the liquid droplets existing in the vicinity of the inner surface of the channel box to the fuel rod, and further, the structure is simple and the limit output is improved. It is possible to provide a fuel spacer and a fuel assembly that can greatly contribute to the above.

That is, according to the invention of claim 1, all or part of the flow tab is provided with an edge for suppressing the inflow of the coolant into the surface on the downstream side of the coolant flow and expanding the negative pressure generated on the same surface. By adopting the cross-sectional shape of No. 3, the edge can suppress the entrainment of droplets from the side of the flow tab. Therefore, the negative pressure on the surface of the flow tab on the downstream side of the coolant flow can be increased, and by widening the negative pressure region, the flow from between the channel box and the flow tab toward the downstream surface of the flow tab can be strengthened.

According to the second aspect of the present invention, the surface of the flow tab on the upstream side of the coolant flow is made into the uneven surface or the surface with projections for dispersing the coolant flow, thereby preventing the trapped droplets from traveling straight. The amount of dispersion suitable for the fuel rod can be increased. Therefore, the cooling efficiency becomes better than that of the conventional flow tub.

According to the third aspect of the present invention, the edge portion for preventing the straight flow of the coolant flow is provided at the tip of the surface of the flow tab on the upstream side of the coolant flow. It is possible to improve the cooling efficiency by increasing the amount of dispersion toward the fuel rods by preventing the straight movement of the fuel cells.

According to the fourth aspect of the present invention, the flow tab is formed so as to cover substantially the entire surface of the gap flow passage formed between the support band and the fuel rod, so that the projected area of the flow tab along the longitudinal direction of the fuel rod. Can be increased to prevent mere passage of the coolant flowing in this portion, thus improving the cooling efficiency. That is, the coolant flowing in the gap between the outermost fuel rod and the spacer band is biased toward the inner side of the fuel, and the coolant in the fuel gap is more and more effectively biased to the inside of the fuel. The thermal margin can be improved.

According to the invention of claim 5, the flow tab is
Compared with the conventional flow tab, the direction of the droplets in the steam flowing in the flow path is compared to the conventional flow tab by adopting a triangular cross-section protruding to the inner surface side of the support band and gradually increasing the cross-section along the flow direction of the coolant. Then, it can be smoothly directed to the fuel rod surface side. As a result, the liquid film flow rate on the surface of the fuel rod is increased, and the resistance of the outermost peripheral flow path is reduced due to the flow tab having a triangular cross section. Can be increased to increase the liquid phase supplied to the fuel rod surface.

According to the sixth aspect of the present invention, the flow tab forming portion of the support band is a movable flow skirt portion in which the coolant flow upstream end moves to the channel box side when the coolant flows. Then, the flow skirt portion is moved to the channel box side by the upward lifting force of the coolant from the lower side. As a result, the liquid phase on the inner wall of the channel box is separated, and the separated liquid phase can improve the cooling efficiency of the fuel rod.
In the state where the coolant does not flow, the lifting force does not act, so that the flow skirt portion is separated from the channel box and is held as a support band, so that there is no hindrance to the assembly and disassembly of the fuel assembly.

According to the seventh aspect of the invention, the flow skirt portion of the support band is rotatably supported by the fuel rod holding portion located at the corner portion of the fuel assembly via the hinge portion. With such a configuration, the smooth operation can be performed by the rotation of the flow skirt, and the liquid phase separation action can be efficiently obtained.

According to the invention of claim 8, the support band comprises:
It is divided into a corner band portion arranged at a corner portion of the fuel assembly and a side band portion arranged on a side portion of the fuel assembly, and a flow tab is formed on this side band portion, and this side band portion is formed. By supporting the corner band portion so as to be rotatable or movable in parallel, the liquid phase peeling action can be obtained with the same simple structure as the invention of the seventh aspect. In addition,
When the entire flow skirt is configured to move to the channel box side, the liquid phase separation action is performed more reliably.

According to the invention of claim 9, the support band is
The corner band of the fuel assembly is divided into a corner band and a side band of the fuel assembly, and the side band is made of an elastic material. By urging the side end (upper end) toward the channel box and forming a guide hole for coolant circulation in this side band, the upper end of the side band is always in contact with the channel box. Similarly to the structure having the flow skirt, the cooling efficiency of the fuel rod can be improved by the liquid phase separation of the inner wall of the channel box. In the case of the present invention, since the upper end portion of the side band portion is in contact with the channel box regardless of the flow of the coolant, it requires a little labor for mounting and the like as compared with the configuration having the flow skirt portion. In short, the liquid phase separation action can be performed more reliably regardless of the coolant flow rate.

According to the tenth aspect of the present invention, the fuel spacer according to any one of the first to ninth aspects is applied as a fuel spacer excluding the fuel spacer located on the most downstream side of the coolant passage, whereby the core is An effective cooling effect can be obtained as a whole.

According to the eleventh aspect of the present invention, the fuel spacer according to any one of the first to ninth aspects is arranged in a region downstream of the coolant flow from the central position in the longitudinal direction of the fuel heating portion of the fuel rod. Thus, an effective cooling effect can be obtained in the upper part of the core where gas-liquid separation is severe.

According to the twelfth aspect of the present invention, the installation region of the fuel spacer according to any one of the first to ninth aspects is set in the region 2/3 of the coolant flow downstream side of the fuel heating portion of the fuel rod. By doing so, a more effective cooling effect at a necessary portion can be obtained.

[Brief description of drawings]

FIG. 1 shows a first embodiment of a fuel spacer according to the present invention, and is a perspective view showing a basic configuration.

FIG. 2 is an explanatory diagram showing an operation of a basic configuration example according to the first embodiment.

FIG. 3 is a perspective view showing a modification of the first embodiment.

FIG. 4 is a perspective view showing a modified example according to the first embodiment.

FIG. 5 is a perspective view showing a modification of the first embodiment.

FIG. 6 is a bottom view showing a second embodiment of the fuel spacer according to the present invention.

FIG. 7 is a sectional view taken along line AA of FIG. 6;

FIG. 8 is a bottom view showing another configuration example of the second embodiment.

9 is a sectional view taken along line BB of FIG.

FIG. 10 is a perspective view showing a configuration of a third embodiment of the fuel spacer according to the present invention.

FIG. 11 is a perspective view showing a different configuration of the third embodiment.

FIG. 12 is a perspective view showing a different configuration of the third embodiment.

13A and 13B are explanatory views showing the operation of the third embodiment.

FIG. 14 is a perspective view showing a basic configuration example of a fourth embodiment of the fuel spacer according to the present invention.

FIG. 15 is a front view of FIG.

16 is a side sectional view of FIG.

FIG. 17 is a plan view of FIG.

FIG. 18 is a perspective view showing a first modification of the fourth embodiment.

FIG. 19 is a front view of FIG. 18.

FIG. 20 is a side sectional view of FIG. 18.

FIG. 21 is a plan view of FIG.

FIG. 22 is a perspective view showing a second modification of the fourth embodiment.

FIG. 23 is a front view of FIG. 22.

FIG. 24 is a side sectional view of FIG. 22.

FIG. 25 is a plan view of FIG. 22.

FIG. 26 is a perspective view showing a third modification of the fourth embodiment.

FIG. 27 is a front view of FIG. 26.

28 is a side sectional view of FIG. 26.

FIG. 29 is a plan view of FIG. 26.

FIG. 30 is a perspective view showing the overall configuration of a fifth embodiment of the fuel spacer according to the present invention.

FIG. 31 is an explanatory view of the operation of the fifth embodiment, showing a state in which the flow skirt portion is closed.

FIG. 32 is an explanatory diagram of the operation of the fifth embodiment, illustrating the state in which the flow skirt portion is open.

FIG. 33 is an explanatory view of the operation of Example 5, showing the state of liquid phase separation on the inner surface of the channel box.

FIG. 34 is a perspective view showing the overall configuration of a sixth embodiment of the fuel spacer according to the present invention.

FIG. 35 is an explanatory view of the operation of the sixth embodiment, showing the closed state of the flow skirt portion.

FIG. 36 is an explanatory view of the operation of the sixth embodiment, showing the opened state of the flow skirt portion.

FIG. 37 is an explanatory view of the operation of the sixth embodiment, showing the state of liquid phase separation on the inner surface of the channel box.

FIG. 38 is a perspective view showing the overall configuration of a seventh embodiment of the fuel spacer according to the present invention.

FIG. 39 is an explanatory view of the operation of the seventh embodiment, showing the closed state of the flow skirt portion.

FIG. 40 is an explanatory view of the operation of the seventh embodiment, illustrating the state in which the flow skirt portion is open.

FIG. 41 is an explanatory view of the operation of Example 7, showing the state of liquid phase separation on the inner surface of the channel box.

FIG. 42 is a perspective view showing the overall structure of an eighth embodiment of the fuel spacer according to the present invention.

FIG. 43 is an explanatory view of the operation of Example 8, showing the state of liquid phase separation on the inner surface of the channel box.

FIG. 44 is an overall view showing an example of a fuel assembly and showing a configuration of a fuel assembly used in a boiling water reactor (BWR).

FIG. 45 is a side view showing the configuration of a conventional fuel spacer.

FIG. 46 is a graph for explaining the thermal limit of the fuel assembly 1.

FIG. 47 is a graph showing a fuel output ratio.

FIG. 48 is a perspective view showing a flow tab of a conventional fuel spacer.

FIG. 49 is an operation explanatory view of the flow tab of the conventional fuel spacer.

FIG. 50 is an operation explanatory view of the flow tab of the conventional fuel spacer.

FIG. 51 is an operation explanatory view of the flow tab of the conventional fuel spacer.

FIG. 52 is an operation explanatory view of the flow tab of the conventional fuel spacer.

FIG. 53 is an operation explanatory view of the flow tab of the conventional fuel spacer.

FIG. 54 is an operation explanatory view of the flow tab of the conventional fuel spacer.

FIG. 55 is an operation explanatory view of the flow tab of the conventional fuel spacer.

FIG. 56 is an operation explanatory view of the flow tab of the conventional fuel spacer.

[Explanation of symbols]

 1 Fuel Assembly 2 Channel Box 3 Fuel Rod 4 Water Rod 5a Cooling Water Inlet 5b Cooling Water Injecting Hole 6 Short Fuel Rod 7 Fuel Spacer 8 Upper Tie Plate 9 Lower Tie Plate 10 Outer Spring 11 Support Band 12 Flow Tab 12a Flow Tab Cooling Surface on downstream side of material flow 12b Surface on upstream side of coolant flow of flow tab 12c Rising portion 12d Projection portion 12e Body portion 13 Liquid film 14 Droplet 15 Negative pressure region 16 Cell 17 Edge 18 V-shaped convex portion 19 Edge 20 Gap flow Road 22 Flow skirt 23 Body part 24 Skirt part 25 Support point pin 26 Hinge 27 Guide 28 Corner band part 29 Side band part 30 Body part 31 Skirt part 32, 33 Support tab 34, 35 Cutout part 36 Coolant flow hole 37 Flow control plate

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location G21C 3/30 GDB Y (72) Inventor Kenetsu Shirakawa 8 Shinsita-cho, Isogo-ku, Yokohama, Kanagawa Company Toshiba Yokohama Office (72) Inventor Takashi Yano 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Stock Company Toshiba Yokohama Office

Claims (12)

[Claims] 1. A square frame-shaped support band for supporting a bundle of a plurality of fuel rods from the outer peripheral side, and a fuel holding portion which is continuously provided inside the support band and holds the fuel rods in a grid-like arrangement with a space therebetween. A fuel spacer for forming a coolant passage along the longitudinal direction between the channel box and the fuel rods and between the fuel rods in a channel box having a quadrangular cross section. At least an edge portion on the downstream side of the coolant flow is provided with an inclined flow tab that directs the flow of the coolant toward the fuel rod side, and from the direction intersecting the coolant flow direction on the surface of the flow tab on the downstream side of the coolant flow. A fuel spacer having a cross-sectional shape with an edge for suppressing the inflow of fuel. 2. A square frame-shaped support band for supporting a bundle of a plurality of fuel rods from the outer peripheral side, and a fuel holding portion which is continuously provided inside the support band and holds the fuel rods in a grid-like arrangement with a space therebetween. A fuel spacer for forming a coolant passage along the longitudinal direction between the channel box and the fuel rods and between the fuel rods in a channel box having a quadrangular cross section. At least an edge portion on the downstream side of the coolant flow is provided with an inclined flow tab for directing the flow of the coolant toward the fuel rod side, and the surface of the flow tab on the upstream side of the coolant flow is an uneven surface for dispersing the coolant flow. Alternatively, the fuel spacer is characterized by having a surface with a protrusion. 3. A square frame-shaped support band that supports a bundle of a plurality of fuel rods from the outer peripheral side, and a fuel holding portion that is connected to the inside of the support band and that holds the fuel rods in a grid-like arrangement with a space therebetween. A fuel spacer for forming a coolant passage along the longitudinal direction between the channel box and the fuel rods and between the fuel rods in a channel box having a quadrangular cross section. In the case where an inclined flow tab for directing the flow of the coolant toward the fuel rod side is provided at least at the edge on the downstream side of the coolant flow, the straight flow of the coolant flow is made at the tip position of the surface of the flow tab on the upstream side of the coolant flow. A fuel spacer, characterized in that an edge portion for preventing the above is provided. 4. A square frame-shaped support band that supports a bundle of a plurality of fuel rods from the outer peripheral side, and a fuel holding portion that is connected to the inside of the support band and that holds the fuel rods in a grid-like arrangement with a space therebetween. A fuel spacer for forming a coolant passage along the longitudinal direction between the channel box and the fuel rods and between the fuel rods in a channel box having a quadrangular cross section. At least an edge portion on the downstream side of the coolant flow is provided with an inclined flow tab for directing the flow of the coolant toward the fuel rod, wherein the flow tab is a gap flow passage formed between the support band and the fuel rod. A fuel spacer having a shape that covers substantially the entire surface of the fuel spacer. 5. A square frame-shaped support band for supporting a bundle of a plurality of fuel rods from the outer peripheral side, and a fuel holding portion which is continuously provided inside the support band and holds the fuel rods in a grid-like arrangement with a space therebetween. A fuel spacer for forming a coolant passage along the longitudinal direction between the channel box and the fuel rods and between the fuel rods in a channel box having a quadrangular cross section. At least an edge portion on the downstream side of the coolant flow is provided with an inclined flow tab for directing the flow of the coolant to the fuel rod side, wherein the flow tab has a triangular cross section protruding toward the inner surface side of the support band, and the coolant is A fuel spacer having a shape in which the cross section gradually expands along the flow direction of the fuel spacer. 6. A square frame-shaped support band for supporting a bundle of a plurality of fuel rods from the outer peripheral side, and a fuel holding portion which is continuously provided inside the support band and holds the fuel rods in a grid-like arrangement with a space therebetween. A fuel spacer for forming a coolant passage along the longitudinal direction between the channel box and the fuel rods and between the fuel rods in a channel box having a quadrangular cross section. A flow tab for directing the flow of the coolant toward the fuel rod is formed at least at the downstream edge of the coolant flow, and the flow tab forming portion of the support band receives the flow of the coolant and has an end on the coolant flow upstream side. A fuel spacer, wherein the portion is a movable flow skirt portion that moves toward the channel box. 7. The fuel spacer according to claim 6, wherein
A fuel spacer, wherein a flow skirt portion of a support band is rotatably supported by a fuel rod holding portion located at a corner portion of a fuel assembly via a hinge portion. 8. The fuel spacer according to claim 6, wherein
The support band is divided into a corner band portion arranged at a corner portion of the fuel assembly and a side band portion arranged at a side portion of the fuel assembly, and a flow tab is formed on the side band portion, A fuel spacer, wherein the side band portion is supported by the corner band portion so as to be rotatable or movable in parallel. 9. A square frame-shaped support band that supports a bundle of a plurality of fuel rods from the outer peripheral side, and a fuel holding portion that is connected to the inside of the support band and holds the fuel rods in a grid-like arrangement with a space therebetween. A fuel spacer for forming a coolant passage along the longitudinal direction between the channel box and the fuel rods and between the fuel rods in a channel box having a quadrangular cross section. A flow band for directing the flow of the coolant toward the fuel rod is formed at least on the downstream side of the coolant flow, wherein the support band includes a corner band part disposed at a corner of the fuel assembly, and The fuel assembly is divided into side band portions arranged on the sides of the fuel assembly, and the side band portions are made of an elastic material and the downstream end of the coolant flow is urged toward the channel box. A fuel spacer characterized in that a guide hole for circulating a coolant is formed in the side band portion. 10. A plurality of fuel rods arranged in a grid pattern, tie plates for fixing and holding both ends of each fuel rod, a channel box having a rectangular cross section for covering these fuel rods and each tie plate, and this channel box. In a fuel assembly comprising: a plurality of fuel spacers that are arranged at intervals along the longitudinal direction within the fuel rods and that form a coolant passage along the longitudinal direction between the fuel rods and between each of the fuel rods, A fuel assembly, wherein the fuel spacers other than those located on the most downstream side of the coolant channel are the fuel spacers according to any one of claims 1 to 9. 11. A plurality of fuel rods arranged in a grid pattern, tie plates for fixing and holding both ends of each fuel rod, a channel box having a rectangular cross section for covering these fuel rods and each tie plate, and this channel box. In a fuel assembly comprising: a plurality of fuel spacers that are arranged at intervals along the longitudinal direction within the fuel rods and that form a coolant passage along the longitudinal direction between the fuel rods and between each of the fuel rods, The fuel spacer arranged in a region on the downstream side of the coolant flow from the central position in the longitudinal direction of the fuel heating portion of the fuel rod,
A fuel assembly comprising the fuel spacer according to any one of claims 1 to 9. 12. A plurality of fuel rods arranged in a grid, a tie plate for fixing and holding both ends of each fuel rod, a channel box having a rectangular cross section for covering the fuel rods and each tie plate, and this channel box. In a fuel assembly comprising: a plurality of fuel spacers that are arranged at intervals along the longitudinal direction within the fuel rods and that form a coolant passage along the longitudinal direction between the fuel rods and between each of the fuel rods, 2/3 of the coolant flow downstream side of the fuel heating portion of the fuel rod
10. The fuel assembly, wherein the fuel spacer arranged in the region of is the fuel spacer according to any one of claims 1 to 9.