JP3356498B2 - Nuclear fuel spacer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear fuel spacer for a fuel assembly which can cool down a fuel rod located inside the fuel assembly.

[0002]

2. Description of the Related Art A typical example of a fuel assembly used in a boiling water reactor (BWR) will be described with reference to FIG.
The BWR fuel assembly 1 has a plurality of fuel rods 2 arranged in a square lattice and is held at a predetermined interval by a plurality of nuclear fuel spacers 3.
To form a binding body, and the binding body is inserted into the rectangular cylindrical channel box 6.

As shown in FIG. 8, a conventional nuclear fuel spacer 3 is a lattice type spacer in which a band-like plate 7 is assembled in a support lattice 8 in a square lattice, or as shown in FIG.
There is known a cellular spacer in which metal tubular cells 9 having a diameter equal to the arrangement pitch of the fuel rods 2 are arranged in a square lattice and joined.

FIG. 8A is a front view, and FIG. 8B is a partial cross-sectional side view. A lantern-type spring 10 is inserted at every other intersection of the band-shaped plate 7, and the band-shaped plate is inserted. 7 is provided with a fixed support member 11 for the fuel rod 2. In addition, the code in FIG.
Numeral 12 denotes a channel spacer protruding outside the support band 8. In FIG. 9, reference numeral 13 denotes a small projection provided in the cell 9, reference numeral 14 denotes a water rod, and reference numeral 15 denotes a spring restraining body for connecting the cells 9 together.

Hereinafter, the nuclear fuel spacer shown in FIG. 8 is called a lattice spacer, and the nuclear fuel spacer shown in FIG. 9 is called a round cell spacer.

As described above, the fuel spacer has a function of keeping a plurality of fuel rods arranged in the channel box at a predetermined interval and suppressing the fluid vibration of the fuel rods caused by being excited by the flow of the coolant. On the other hand, the spacer member is located in the gap between the fuel rods serving as the coolant flow path, and serves as an obstacle to narrow the flow path, and therefore has a flow resistance of the coolant.

[0007] The flow resistance in a fluid is smaller than that of a water single-phase flow.
Under the two-phase flow condition where steam and water are mixed and flow at high speed, several tens
In the BWR fuel assembly in which steam and water flow in a mixed manner, the ratio of the spacer to the flow resistance of the assembly is as large as about 20%. Since the pressure loss reduction of the fuel assembly is important for the design of a small-capacity circulating pump that circulates the coolant through the core, reducing the pressure loss of the spacer has been an issue.

[0008] The increase in the spacer flow resistance adversely affects the stability of the flow of the coolant at low flow rates such as in natural circulation. It also affects the power limit of the fuel assembly.

As described above, among the fuel assembly components, the fuel spacer has a large effect on the pressure loss characteristics when the coolant in the fuel assembly flows, and is an important component in terms of fuel stability and cooling characteristics. Especially during normal reactor operation, reducing the power of the circulating pump that sends coolant to the assembly, that is, improving the pressure loss characteristics of the fuel spacer directly leads to improvement of the power generation efficiency of the plant. Has been made conventionally.

The round cell type spacer shown in FIG. 9 is formed by arranging a plurality of circular tubes having a diameter corresponding to the fuel rod pitch vertically and horizontally and circumscribing them. The spacer member is closer to the fuel rods than the portion is located in the center of the space between the fuel rods, and there is no member in the center of the space between the fuel rods.

The flow of coolant in the fuel assembly is such that steam flows between each fuel rod at a high speed, and water flows over the fuel rod surface at an average thickness.
It flows as a thin liquid film of about 0.2 mm to 0.6 mm. As shown in FIG. 10, the steam flow velocity in the fuel rod space has a distribution such that the flow velocity is the slowest on the surface of the fuel rods 2 and the fastest in the center between the fuel rods 2.

In the case where there is no obstacle in the flow path, for example, the flow velocity becomes slow on the wall surface (y = 0). Flow resistance R is typically expressed as R = (resistance coefficient C _D) × (the speed V of the fluid) (projected area S with respect to a plane perpendicular to the flow) × (density of the fluid ρ) × ^2/2, the flow velocity V is Works square with flow resistance.

Therefore, in the round cell type spacer in which the spacer member does not exist in the center of the space between the fuel rods having the highest steam flow velocity, the vapor near the fuel rod having the slow flow velocity collides with the spacer member, so that the center of the fuel rod space. The flow resistance is smaller than that of a lattice spacer having a spacer member.

By the way, the following first to third measures have been proposed as means for improving the limit output.
First, the liquid film on the inner surface of the unheated channel box that does not contribute to cooling the fuel rods is stripped off and used as a coolant for the fuel rods near the channel box. To do this, a plate called a flow scraper or a flow skirt is attached to the spacer, this is brought into contact with the inner surface of the channel box, the separated liquid (liquid film) is separated from the surface of the channel box, the downstream end of the spacer outer frame (band) or the like. This is a method in which a claw-shaped protrusion called a flow tab provided at the downstream end of the outer frame of the spacer is scattered into the mainstream and adheres to the surrounding fuel rods, thereby improving fuel rod cooling.

Second, as shown in FIG. 11, a torsion plate 16 and blades are attached to a spacer band 8 in a flow path space surrounded by fuel rods at the lower end of the spacer, and droplets contained in the main steam are captured by these. Then, the liquid 17 is directed toward the fuel rod 2 by a swirling flow generated by the torsion plate 16 or the blade or a centrifugal force acting on the liquid 17 attached to the surface of the plate or the blade, and is used for cooling the fuel rod 2.

Thirdly, the gap between the fuel rod and the channel is maintained at a predetermined interval or more as designed. The gap between the fuel rod and the channel is devised by a projection attached to the outer frame of the fuel spacer so as not to be less than a certain distance.

However, a play required for fuel assembly is provided between the outer diameter of the spacer and the inner diameter of the channel box. For this reason, the interval between the fuel rod facing the channel side and the channel box may become uneven depending on how the fuel assemblies are biased in the channel box.

Therefore, when the flow path becomes narrow, the flow of the coolant becomes poor, and there is a concern that the cooling capacity is reduced. In order to reduce the irregularity as much as possible, a spring is provided between the spacer and the channel, or a device for absorbing the play between the channel and the spacer due to thermal expansion has been devised.

[0019]

The grid type spacer eliminates a sudden change in the flow path area due to the spacer member by protruding a member in the center of the fuel rod space having a high flow velocity into a chevron in the flow direction of the coolant so as to eliminate flow resistance. To reduce the spacer pressure loss.

Other methods of reducing the flow resistance of the spacer include reducing the thickness of the spacer member, or partially removing the member to reduce the projected area of the spacer member in the direction perpendicular to the coolant flow. Is reduced.

Although the spacer pressure loss has been devised as described above, in the case of a round cell type spacer, a spacer is formed by circumscribing a cylindrical cell having a constant diameter corresponding to the fuel rod pitch. The member cannot be brought close to the vicinity of the fuel rod having a low steam flow rate.

Regarding the round cell type spacer, for example,
JP-A-59-65287 discloses a "fuel assembly spacer". That is, in this publication, the coolant stagnates in order to prevent accumulation of dust between adjacent cells,
In order to prevent dirt from accumulating between the cells at the circumscribed portion, the circumscribed portion is protruded only at both ends of the ferrule, and a slight gap is provided between the circumscribed portion cells. Further, since only the both ends of the cell are slightly protruded, the members of the ferrule main body and the members at the ends are arranged so as to increase the projected area of the spacer of the circumscribed portion.

In the grid spacer with projections, the effect of reducing the pressure loss is remarkable as compared with other spacers including a round cell and a grid type due to the reduction of the flow area change rate due to the projections. However, since the member is located in the center of the fuel rod space where the steam flow velocity is the fastest, there is room for low pressure loss. As described above, there has been a problem that the conventional proposal for reducing the flow resistance of the spacer does not provide a sufficient pressure loss reducing effect.

On the other hand, the conventional contrivance for improving the limit output has the following problems. The device for removing the liquid film from the inner surface of the channel box (flow scraper, flow skirt, etc.) is used only for cooling the fuel near the channel box, especially on the fuel surface facing the channel box. Even if the temperature rise (dryout) due to the disappearance of the liquid film on the surface, the peeled liquid film did not reach the inside of the assembly, so that there was no effect in improving the limit output.

Further, since the distance between the flow scraper, the flow skirt and the channel box cannot be reduced to zero in assembling the fuel assembly, a certain amount of play is provided. However, since the liquid film is thin, about 0.1 mm to 1 mm is required. Most of the liquid passed through the play area (0.1 mm), and the liquid on the surface of the channel box could not be sufficiently removed.

Similarly, there is a contrivance to provide projections and depressions on the inner surface of the channel box to peel off the liquid film flowing through the inner surface of the channel box. However, this method is effective only for the fuel rod facing the channel box, and is similar to the above. There are issues.

Further, in the mechanism for trapping liquid droplets such as blades and torsion plates and generating a swirling flow, a plate material having a uniform thickness is used. Length, twist pitch, angle, blade tip shape.

For example, in the case of using a torsion plate, the amount of liquid scattered by centrifugal force from the middle of the blade is almost constant no matter what factor is changed. There was no design flexibility to get more, and the range of factors for adjusting to optimal characteristics was narrow.

Further, the blades having a uniform cross section become weaker in strength and fatigue fracture when the length is increased, and the blades fracture due to fatigue during the operation of the reactor and are mixed into the coolant, so that the fuel cladding tube and other parts are damaged. There was concern that equipment could be damaged.

Further, in the device for positioning the fuel assembly, a spring is attached to the spacer or the fuel assembly is developed by thermal expansion.
It has been considered to provide a mechanism for absorbing the play between the channel box and the spacer exclusively for positioning, and this has been a factor that causes fuel cost, an increase in the number of manufacturing steps, and a decrease in neutron economy (neutron absorption).

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a nuclear fuel spacer in which a flow resistance is reduced and a limit output is improved.

[0032]

The invention according to claim 1 is
In a nuclear fuel spacer plurality of cells are arranged in a substantially lattice-like to form the fuel rod insertion passage for inserting a plurality of fuel rods at substantially equal intervals to each independently, it said cell is a flat surface of the four sides, the four sides each cross-section consists of a short tube substantially octagonal with the inclined surface of the four sides curved convexly inward, the fuel rod insertion path is the four pair of the cell between the flat surfaces of,
Flat surface with one cell and the other cells are butted each respectively and Ri Do from the cylindrical portion, each formed by the outer inclined surface of the four sides via the flat surface, opposite of the cell
Insertion hole for liquid guide member of flow scraper on flat surface
Are provided with a step, and the insertion holes are inserted into these insertion holes.
The inner member is inserted inclining upward from the outermost periphery of the cell
The flow scraper is inserted into the cell
It is characterized by being arranged .

According to a second aspect of the present invention, the flow screen
The plate has a plate-shaped main body and a liquid guide provided on the plate-shaped main body.
And a member . Invention according to claim 3
Is one of the diagonal lines of the flat surface joining the plurality of cells.
Inserting a restraint plate on the flat surface in a direction perpendicular to the flat surface
It is characterized by becoming .

According to a fourth aspect of the present invention, the restraining plate has a belt shape.
A flat plate with multiple slits perpendicular to its longitudinal direction
The material of which is smaller than the coefficient of thermal expansion of the cell.
It is characterized by having an expansion coefficient . Invention according to claim 5
Has a plate thickness cross-sectional shape on the downstream side where the fluid of the restraint plate flows.
Is attached with a non-uniformly formed torsion plate.
Sign .

The invention according to claim 6 is characterized in that the torsion plate has
V-shaped protrusions or protrusions along the longitudinal direction on both sides of the plate
It is characterized by being formed . Invention according to claim 7
Has a large thickness at the center or at both ends of the torsion plate.
It is characterized by being formed so as to be uniform .

[0036]

[Action] cross section a substantially octagonal shape cells as four pair,
The flat surfaces of one cell and the other cell are butted against each other, and the inclined surfaces of the different cells are adjacent to each other through the respective flat surfaces, and a cylindrical portion is formed outside the four inclined surfaces. You. That is, since the curvature of the inclined surface is a quarter circle, it is the same as a circle when four pieces are combined.

By using the cylindrical portion as the fuel rod insertion passage, the length of the flat surface can be made closer to the fuel rod until it comes into close contact with the fuel rod, and the cell can be located near the fuel rod with a slow steam flow rate. That is, if the velocity of the steam colliding with the cell decreases, the flow resistance of the spacer decreases due to the relationship between the flow resistance R and the flow velocity V, and the pressure loss of the spacer can be reduced.

Further, an insertion hole for the liquid guide member of the flow scraper is provided on the flat surface of the cell, and the liquid flowing through the inner surface of the channel box can be carried to the center of the fuel bundle by inserting the liquid guide member into the insertion hole. .

Further, by inserting a thermal expansion positioning mechanism in a direction perpendicular to one of the diagonal lines of the flat surface of the cell, the thermal expansion positioning mechanism is expanded or reduced in the direction of the channel box depending on the temperature. The gap with the channel box can be changed.

Further, by providing a blade-like torsion plate having a different plate thickness on the downstream side of the support band or the restraining plate, the liquid film flow on the surface of the torsion plate is blocked at the plate thickness portion, or the liquid film is reduced. It can be peeled off, whereby the flow of the liquid film can be controlled and the characteristics can be adjusted.

[0041]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a nuclear fuel spacer according to the present invention will be described with reference to FIGS. FIG. 1 (a)
FIG. 3 shows only a cross section of a main part of the nuclear fuel spacer according to the present embodiment with the fuel rods inserted therein. The overall configuration is substantially the same as the conventional round cell type spacer shown in FIG. The present embodiment differs from the round cell type spacer shown in FIG. 9 in that the shape of the cell is different. Therefore, only the different points will be described, and the description of the overlapping portions will be omitted.

The cells 18 used in this embodiment are the first cell 18a shown in FIG. 2B and the second cell 18a shown in FIG.
b. As shown in the perspective view of FIG. 2A, the appearance of these cells 18a and 18b is substantially as if each side of the square cube was recessed inward and each corner was cut off to form a flat surface. It has an octagonal cube structure.

That is, the first and second cells 18a, 18
b has a flat surface 19 with four sides as if each corner was cut off,
Inclined surface of four sides as if each side was depressed inward and curved
It consists a short pipe which is formed in a substantially octagonal shape and a 20. As shown in FIG. 2 (c), the second cell 18b has four small protrusions 21 extending outward and inward at the center of the inclined surface 20 in total, two at the top and bottom.

The fuel rods insertion passage 22 is formed outside of one of the cell 18 and the other flat surface 19 of the cell 18 of abutted to each other and the inclined surface 20 of the 4 adjacent sides through the flat surface 19, respectively It is a cylindrical part. The curvature of the inclined surface 20 of the cell 18 is 1/4 circle, and a perfect circle is formed by connecting four inclined surfaces 20 continuously.

However, as shown in FIG.
Cells 18a and second cells 18b are arranged vertically and horizontally to form a flat surface 19.
And at the intersection point where they match, FIG. 1 (b)
The holding member 23 having elasticity shown in (1) is fitted, and the flat surface 19 is held to form the fuel rod insertion passage 22 in a lattice shape, thereby constituting a nuclear fuel spacer. The holding body 23 is formed with an insertion portion 23a for vertically inserting the flat surface 19 and an elastic chevron 23b at the center. The fuel rods 2 are inserted into the fuel rod insertion passages 22 to form a fuel bundle of a fuel assembly.

In this way, by making the partial length of the flat surface 19 connecting the inclined surface 20 of 1/4 circle close to the gap of the fuel rod 2, the cell 18 is brought into close contact with the fuel rod 2 as shown in FIG. As a result, the cell 18 can be located near the fuel rod 2 having a low steam flow rate.

If the velocity of the steam colliding with the cell 18 decreases, the flow resistance of the spacer decreases due to the relationship between the flow resistance R and the flow velocity V, and the pressure loss of the spacer can be reduced. Also cell 18
Is made of a material having a high strength such as inconel from zircaloy having low neutron absorption, and by reducing the thickness, the projected area of the members of the cell 18 can be reduced, and the pressure loss can be further reduced.

On the other hand, there is a concern that the flow of the vapor or liquid film near the fuel rod may be stagnated due to the decrease in the gap between the cell and the fuel rod surface, but the liquid film on the surface has an average thickness of 0.2 mm or less.
Since it is about 0.6 mm, it can pass sufficiently even if the gap is narrower than the conventional round cell type spacer.

As shown in FIG. 10A, the flow path wall (fuel rod)
And the distance between the obstacle (obstacle) (spacer)
Even if it is about 0.75 mm, the gas phase passes through the gap between the cell and the fuel rod, and it can be seen that even if the cell is brought closer to the fuel rod surface than the conventional spacer, the coolant is blocked and the cooling performance is not significantly impaired. .

Further, as shown in FIG. 2D, a taper processing 25 is applied to the outside of the cell 18 on the upstream side of the coolant (the surface facing the fuel rod 2) so that the gap between the cell 18 and the fuel rod 2 can be reduced. A thick liquid film 24 can be taken into the fuel rod 2 side.

In this embodiment, a plurality of cells are arranged in a grid and the periphery is surrounded by a support band. However, when each cell is individually joined and fixed, the support band is not necessarily required. It does not mean that.

Next, a second embodiment of the nuclear fuel spacer according to the present invention will be described with reference to FIGS. The second embodiment is a flat surface 19 against direction of the cell 18 shown in the first embodiment,
19 respectively provided interpolation <br/> hole 26 has a step as shown in FIG. 3 (a), shown in FIG. 3 (c) and 4 (b) the insertion hole 26 of Katsuko these The liquid guide member 28 of the funnel-shaped flow scraper 27 is inserted so as to be inclined upward from the outermost periphery of the cell 18.

As shown in FIGS. 3B and 4A, the flow scraper 27 is arranged near the channel box 6. The position of the insertion hole 26 differs depending on the opposing flat surface 19 as shown in an enlarged manner in FIG. In other words, the front insertion hole 26 has a step located below, and the rear insertion hole 26 has a step located above. This insertion hole 26
3A and 3B insert the tubular liquid guide member 28 of the flow scraper 27 as shown in FIGS. 3B and 4A.

The flow scraper 27 is shown in FIG.
As described above, the plurality of liquid guide members 28 are substantially 45
Shaped in parallel so that it can be bent at an angle of °
It is in shape. Then, as shown in FIG. 3 (b), arranged so that the tip of the plate-like body 27a on the inner surface of the channel box 6 is wetted body guide member 28 is opened through the upper insertion holes 26 of the cell 18 Is done. The liquid outflow hole 29 is formed near the channel box 6 side to the plate-like body 27a, off
The low scraper 27 is attached to a support band (not shown).

Thus, according to the present embodiment, as shown in FIG. 3B, the liquid film 24 peeled off from the inner surface of the channel box 6 can be supplied to the inside of the fuel bundle of the fuel assembly. That is, the liquid film 24 rising on the inner surface of the channel box 6 flows into the flow scraper 27, and a part of the liquid film 24 flows out as the liquid 17 from the liquid outlet hole 29, but the other liquid films 24.
Is converted into a liquid 17, passes through the liquid guide member 28, flows out from the opening end thereof, and is sent to the center of the fuel bundle.

Thus, the conventional channel box 6
The liquid 17 that has been supplied and used only to the space between the fuel bundle 2 and the outermost fuel rod 2 reaches the center of the fuel bundle, and can be used for suppressing dryout inside the fuel bundle, thereby improving the limit output.

The liquid guide member of the flow scraper 27
Not all of the 28 tips are required for the space of the bundle of fuel rods, and need only reach the second or third row from the outermost periphery which is particularly severe in heat. Further, by providing the liquid outflow hole 29 in the middle of the flow scraper 27, a part of the liquid 17 can be supplied halfway to the tip.

Next, a third embodiment of the nuclear fuel spacer according to the present invention will be described with reference to FIG. This third embodiment is similar to the first embodiment.
As shown in FIG. 5 (a), the first and second cells 18a and 18b in the embodiment of FIG.
A nuclear fuel spacer is constructed according to the first embodiment by inserting the restraint plate 30 shown in FIG.

The restraining plate 30 is formed by forming a plurality of slits 31 in a direction perpendicular to the longitudinal direction of a band-shaped flat plate having a width to be inserted into the joint of the flat surface 19. Then, the restraint plate 30 is inserted and fixed to the flat surface 19 of each of the cells 18a and 18b. Restraint plate 30
Is inserted only in the vertical direction as shown in FIG. 5A, and is not inserted in the horizontal direction.

However, the restraint plate 30 may be only in the horizontal direction, but in this case, it is not inserted in the vertical direction, and only the diagonal line in any one direction is used. The material of the restraint plate 30 has a smaller coefficient of thermal expansion than the material of the cell 18. When the cell 18 is, for example, Inconel, the restraint plate 30 is, for example, Zircaloy.

According to the third embodiment, when the operating temperature of the reactor rises from about 20 ° C. to about 300 ° C. in FIG.
As shown by (c), the cell 18 is deformed by thermal expansion as shown by a dotted line a, and a binding force is exerted as shown by an arrow b.

Since the cell 18 expands in the direction opposite to the restraining force, it is not necessary to provide a positioning mechanism such as a spring or a thermal expansion mechanism on the outer frame of the spacer exclusively for positioning the spacer as in the conventional example.

In the above-described embodiment, a rotating blade-like torsion plate, which will be described later, is provided downstream of the restraint plate 30 so that the spacer positioning mechanism and the limit output can be improved.
30 can be shared.

The flow scraper 27 used in the second embodiment can be used. In this case, when assembling a fuel assembly performed at normal temperature, a clearance required for assembly is secured between the flow scraper 27 and the channel box 6, and the flow scraper 27 in the expansion direction is channeled in a high temperature state during actual operation of the machine. The liquid film on the inner surface of the channel box 6 is pressed against the box 6 very efficiently.
Peel 24.

Further, the restraint plate 30 extends in one direction. However, when the nuclear fuel spacers are installed in the axial direction of the fuel assembly, if the directions of the thermal expansion are shifted by 90 °, the fuel bundle can be centered. And can be positioned in the channel box 6
The liquid film 24 in each direction can be used.

In the conventional fuel assembly positioning mechanism, a means is provided on a spacer support band (outer frame of the spacer) of a spring or a thermal expansion device, and protrudes (presses) toward the channel box 6. However,
The gap between the flow scraper and the channel box is the same as when the fuel bundle is installed in the channel box.

Further, it is difficult for the positioning device and the flow scraper to buffer and provide the spacer function simultaneously at the same time. However, in the present embodiment, since both do not interfere, the spacer function can be sufficiently provided.

Next, the torsion plate used for the conventional spacer and the torsion plate used for the spacer of the present invention will be described with reference to FIG. FIG. 6A shows a conventional twisted plate 16a.
(B) to (f) are the torsion plates 16b to 16f of the present invention. The torsion plates 16b to 16f of the present invention are attached to the support band 8 as shown in FIG.
It is to be attached to. In addition, each figure is a side view,
This side view is shown together with the top view seen from the direction of the thick arrow 32.

The conventional torsion plate 16a shown in FIG. 6 (a) is obtained by giving a rectangular flat plate a twist of 180 ° from the center.

The torsion plate 16b of the present invention shown in FIG. 6 (b) is formed by forming four steps of V-shaped protrusions 33 on a flat plate in the vertical direction so that the liquid film is scattered on the way.

Similarly, the torsion plate 16c shown in FIG. 6 (c) is formed by forming a long projection 34 at the center of both sides of the flat plate to improve strength and fatigue strength.

Similarly, the torsion plate 16d shown in FIG. 6 (d) has an I-shaped thick portion 35 having a large thickness at both ends of the flat plate to improve the strength and the fatigue strength and to improve the liquid film from the side. The scattering is suppressed, and a large amount is emitted from the end.

Similarly, the torsion plate 16e shown in FIG. 6 (e) is formed with a thick plate portion 36 whose thickness is gradually increased at both ends of the flat plate. It was made.

Similarly, the torsion plate 16f shown in FIG. 6 (f) has two projections 37 having a large thickness on both sides of the flat plate.
This is to improve the strength and to control the scattering ratio between both side surfaces and the terminal.

However, the spacer according to the present invention uses a torsion plate obtained by twisting a flat plate having a non-uniform thickness and a non-uniform cross section as the swirling blade. As shown by the direction (direction) of the arrow and the length (amount) of the arrow, the position and amount of liquid that is trapped on the surface of the swirling blade and sticks to the surface and flows from the blade is determined by plastic deformation on the surface of the torsion plate. The flow direction is restricted to some extent by the provided convex or concave pattern.

Since the flow can be changed by this, the flexibility of the design to increase the number of captured droplets from the middle of the blade or from the tip is increased, and it is possible to adjust the droplet scattering characteristics of the blade optimally. Becomes

For example, the torsion plate 16b shown in FIG. 6B is arranged, for example, at the center of a space formed by four fuel rods. In a boiling water reactor, about two-thirds of the total length of the fuel assembly, the steam generated by boiling flows through the center of the space formed by four fuel rods with droplets, and water flows through the fuel rods and channels. It is a flow called an annular spray flow attached to the box surface.

When the torsion plate 16b is set in the space, the droplets flying in the vapor flow collide with the blades and are trapped to form a liquid film. Since the liquid film is a torsion plate that flows by being pulled by the flow, a centrifugal force is generated to generate a flow toward the outside of the torsion plate. As a result, the flow is as shown by the arrow in FIG. At this time, V as shown in FIG.
Lever is formed shaped protrusions, so that the scattered twisting from the side of the blade to the fuel rod side while not move too long distances.

On the other hand, as shown in FIGS. 6 (d) and 6 (e), since the scattering from the side surface where both ends of the plate are thickened is suppressed, the amount of liquid reaching the downstream end of the torsion blade increases. Even at the downstream end, the fuel is scattered in the fuel rod direction by the centrifugal force.

In the torsion portion, the flow path is narrowed by the volume of the torsion plate, and the flow velocity of the steam is high. Therefore, the ratio of the droplets scattered from the torsion plate to the steam flow before reaching the fuel rods is reduced. Many. Therefore, it is possible to effectively attach the droplets to the fuel rods by shifting the droplet scattering position to near the downstream of the blade where the steam flow rate falls.

Further, by making the cross-sectional shape of the torsion plate non-uniform, the strength of the torsion plate can be increased, and by increasing the length of the torsion plate, the strength surface and the fatigue fracture surface due to fluid vibration can be reduced. The performance degradation can be covered, and the situation where the torsion plate is broken during the operation of the reactor and gets mixed in the coolant and damages the fuel cladding tube and other equipment can be prevented.

According to the present invention, the flow scraper
Effective use of coolant in the channel box for fuel rod cooling
Coolant that contributes to thermally demanding fuel rod cooling
To improve fuel rod cooling and limit the fuel assembly
The output increases . Also, due to the thermal expansion effect of the spacer,
Press the flow scraper against the inside of the channel box
The liquid film on the inner surface of the channel box can be reliably removed.
I can .

[0083]

[0084]

[0085]

[0086]

[0087]

[Brief description of the drawings]

1A is a cross-sectional view partially showing a main part of a first embodiment of a nuclear fuel spacer according to the present invention, and FIG.
FIG.

2A is an enlarged perspective view showing a cell body in FIG. 1A, FIG. 2B is a top view and a side view showing a first cell in FIG. 1A, and FIG. Is a top view and a side view similarly showing a second cell, and (d) is a partial cross-sectional view for explaining the same operation when the end face of the cell is tapered.

3 (a) is a perspective view showing a cell in a second embodiment of the nuclear fuel spacer according to the present invention, FIG. 3 (b) is a partial cross-sectional view of the cell of FIG. 3 (a) combined with a flow scraper, and FIG. The perspective view which shows the flow scraper of (b).

FIG. 4 (a) shows the cell shown in FIG. 3 (a) and FIG.
FIGS. 3B and 3C are cross-sectional views showing the relationship with the flow scraper shown in FIG. 3B, and FIG. 3B is a perspective view showing the flow scraper shown in FIG. 3C in detail.

FIG. 5A is a cross-sectional view partially showing a main part of a third embodiment of the nuclear fuel spacer according to the present invention, and FIG.
FIG. 3C is a perspective view showing the restraint plate, and FIG. 3C is a conceptual diagram for explaining the function of the cell in FIG.

6 (a) is a top view and a side view showing a torsion plate of a conventional nuclear fuel spacer, and FIGS. 6 (b) to (f) are a top view and a side view showing a torsion plate of a nuclear fuel spacer according to the present invention.

FIG. 7 is a partially cutaway perspective view showing a nuclear fuel assembly for a boiling water reactor for explaining a conventional nuclear fuel spacer.

FIG. 8A is a front view showing a first example of a conventional nuclear fuel spacer, and FIG. 8B is a side view showing part of FIG.

FIG. 9 is a cross-sectional view showing a second example of a conventional nuclear fuel spacer.

FIG. 10 is a conceptual diagram showing a comparison between vapor velocity distributions of nuclear fuel spacers of a conventional example and an example of the present invention.

FIG. 11 is a side view showing a torsion plate type swirling blade in a conventional nuclear fuel spacer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Fuel assembly, 2 ... Fuel rod, 3 ... Nuclear fuel spacer, 4
... upper tie plate, 5 ... lower tie plate, 6 ... channel box, 7 ... band-shaped plate, 8 ... support band, 9 ... metal tubular cell, 10 ... lantern type spring, 11 ... fixed support member, 12 ... channel spacer , 13 ... small protrusion, 14 ...
Water rod, 15… Spring restraint, 16, 16a-16
f: twisted plate, 17: liquid, 18: cell (first embodiment), 18a
1st cell, 18b 2nd cell, 19 ... flat surface, 20 ... inclined surface, 21 ... small protrusion, 22 ... fuel rod insertion passage, 23 ... holding body, 24
... liquid film, 25 ... taper processing, 26 ... insertion hole, 27 ... flow scraper, 27a ... plate-shaped main body, 28 ... liquid guide member, 29 ... liquid outflow hole, 30 ... restraint plate, 31 ... slit, 32 ... thick arrow , 33 ...
V-shaped convex part , 34 ... vertical protrusion, 35 ... I-shaped plate thick part, 36
... thick plate thickness part, 37 ... two projections.

Claims (7)

(57) [Claims] 1. A plurality of fuel rods are inserted at substantially equal intervals.
A plurality of cells each independently forming a fuel rod insertion passage
In a nuclear fuel spacer arranged in a lattice pattern,  The cell is 4SideWith a flat surfaceEach between these four flat surfaces
on the insideConvexCurved 4SideSlopeWhenThe cross section with
BobOctagonalConsisting of short tubes,  In the fuel rod insertion passage, one set of four cells is provided.
And the other cell's flat surfaceEachButted
AndEachThrough the flat surfaceSaid4SideOut of the slope
From the cylindrical part formed on the sideAnd Liquid plan of flow scraper on opposite flat surface of the cell
An insertion hole of the inner member is provided with a step, and
The liquid guide member faces upward from the outermost peripheral side of the cell in the hole
The flow scraper is inserted with the
Being inserted and placed in the cell Nuclear fuel characterized by the following
Spacer. 2. The flow scraper comprises a plate-shaped main body,
2. The nuclear fuel spacer according to claim 1, further comprising a liquid guide member provided on said plate-shaped main body . 3. The nuclear fuel spacer according to claim 1, wherein a restraining plate is inserted into one of the diagonal lines of the flat surface joining the plurality of cells in a direction perpendicular to the flat surface. . Wherein said constraining plate in strip flat, a plurality of slits are formed in the longitudinal direction perpendicular to the direction of its, and Turkey the material is to have a small thermal expansion coefficient than the thermal expansion rate of the cell The nuclear fuel spacer according to claim 3, wherein: The downstream fluid flow of 5. Before SL constraining plate, the nuclear fuel spacer according to claim 4, characterized by being fitted with a torsion plate thickness sectional shape is non-uniformly formed. 6. A nuclear fuel spacer according to claim 5, wherein the torsion of V-shaped projections or projections in the longitudinal direction on both sides of the plate in the plate is formed. 7. A nuclear fuel spacer according to claim 5, characterized in that it is uniformly formed so as the plate thickness increases at the center or both ends of the plate to the torsion plate.