JPH06214073A - Nuclear fuel spacer - Google Patents

Abstract

PURPOSE:To provide a nuclear fuel spacer with low pressure loss capable of reducing flow resistance. CONSTITUTION:A nuclear fuel spacer has cylindrical cells 24 arranged in 8 rows and 8 columns in a spacer band, circumscribing parts 25 protruded outward are uniformly formed on the cell body part 34 of the cylindrical cell 24, two fixed support parts 26 protruded inward for supporting fuel rods 2 are formed between the circumscribing parts 25, 25, and one elastic support part 27 is also formed. The curvature R of the body part of the cylindrical cell 24 is set smaller than 1/2 of the pitch P between the fuel rods 2, 2. On the circumscribing part 25, projection parts with sharp top ends are formed over the whole length of the cylindrical cell 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cell type nuclear fuel spacer incorporated in a reactor fuel assembly for maintaining fuel rods at regular intervals.

[0002]

2. Description of the Related Art Among fuel assemblies of a nuclear reactor, a fuel assembly used in a boiling water reactor (BWR) is illustrated.
14, the nuclear fuel spacer will be described with reference to FIGS. 15 (a) and 15 (b).

A BWR fuel assembly 1 is constructed by arranging fuel rods 2 in 8 rows and 8 columns, an upper tie plate 3, a lower tie plate 4 and a lattice type nuclear fuel spacer 5. Fuel rod 2 is made by burning low-enriched uranium into pellets,
It is inserted into a fuel cladding tube, and a zirconium liner cladding tube is used as the fuel cladding tube.

The lattice type nuclear fuel spacer 5 is for keeping the interval between the plurality of fuel rods 2 at a specified width, and the upper tie plate 3 and the lower tie plate 4 support the upper and lower portions of the fuel rods 2 and a channel box. 6 is inserted. One or two of the plurality of fuel rods 2 are water rods 7.
Has been replaced by.

The lattice type nuclear fuel spacer 5 has a square spacer band 8 as shown in FIGS. 15 (a) and 15 (b).
And a grid plate 9 vertically and horizontally combined in the spacer band 8. The grid plate 9 has a square compartment 10
Fixed support 11 for holding fuel rod 2 to be inserted therein
And an elastic support member for pressing the fuel rod 2 against the fixed support portion 11.
12 are attached to the intersections of the grid plates 9.

The spacer band 8 is provided with a plurality of leaf-shaped projections 13 projecting outward on the channel box 6 side in order to secure a space between the channel box 6 and the outermost fuel rod 2. The leaf-shaped projection 13 is generally a fixed portion having a constant height formed by plastically deforming the spacer band 8.

On the other hand, at the time of assembling the fuel assembly 1, since the channel box 6 is inserted and assembled at the end, the inner width of the channel box 6 is wider than the outer width of the leaf-shaped projections 13, and the fuel assembly after assembling is completed. Within the body 1 there is a small (~ 0.5 mm) gap in the fuel rod 2.

Therefore, when the reactor is operating, the designed gap (4 mm) between the fuel rods 2 and the channel box 6 at the outermost periphery of the fuel assembly, that is, the coolant passage area at the outermost periphery is cooled if manufacturing errors are included. The material flow rate can be changed. When the area of the coolant passage becomes narrow, it becomes difficult for the coolant to flow, the amount of coolant for removing heat from the fuel rods 2 facing the passage decreases, and the heat becomes severe.

On the other hand, a round cell type nuclear fuel spacer 14 as shown in FIGS. 16 and 17 is known. This round cell type nuclear fuel spacer 14 has a diameter within the spacer band 8 of the fuel rods 2.
The metal tubular cells 15 having the same arrangement pitch as the above are arranged and joined in a square lattice.

The metal tubular cell 15 is provided with a fixed support portion 11 and a leaf spring 16 to elastically support the fuel rod 2. In addition, a spacer tab 17 is provided around the spacer band 8.
Is projected.

In this round cell type nuclear fuel spacer 14, the spacer member is a fuel rod, as compared with the member of the lattice type nuclear fuel spacer 5, especially the intersection of the lattice plates 9 is located at the center of the fuel rod 2 space. 2, there is no member at the center of the fuel rod 2 space.

As another example of the metallic tubular cell 15 in the round cell type nuclear fuel spacer 14, the round cells 18 and 18a shown in FIGS. 18 (a) and 18 (b) are known. This round cell 18,18
The letter a is quoted from FIGS. 10A and 10B of Japanese Examined Patent Publication No. 3-035640. The round cells 18 and 18a are called ferrules, and the upper and lower end portions 19 and 20 are larger in cross-sectional dimension, for example, diameter, than the main body 21 portion.

This creates a space or gap 22 between one round cell 18 and the adjacent round cell 18a, which gap 22 prevents dirt from collecting between the round cells 18, 18a. The coolant is allowed to circulate.
Note that reference numeral 23 in the drawing indicates a circumscribed portion.

[0014]

As described above, a plurality of nuclear fuel spacers are arranged in the fuel assembly, the fuel rods 2 are kept at a predetermined interval, and the fluid vibration of the fuel rods caused by being excited by the flow of the coolant is generated. There is a function to suppress.

On the other hand, the spacer member is located in the gap between the fuel rods serving as the coolant flow passage and serves as an obstacle for narrowing the flow passage, thus providing flow resistance of the coolant. The flow resistance in the fluid is several tens of times higher than that of the water single-phase flow under the two-phase flow condition in which steam and water are mixed and flows at high speed. Therefore, the BWR fuel assembly in which steam and water are mixed and flow In that case, the spacer accounts for a large proportion of the flow resistance of the aggregate.

Since reduction of pressure loss of the fuel assembly is important for designing a small capacity of the circulation pump for circulating the coolant in the core,
Reduction of the pressure loss of the spacer has been an issue. In addition, the increase in spacer flow resistance adversely affects the stability of coolant flow at low flow rates such as natural circulation. Further, it also affects the limit output of the fuel assembly.

As described above, among the fuel assembly constituent parts, the fuel spacer has a great influence on the pressure loss characteristics when the coolant in the fuel assembly flows, and is an important part in terms of fuel stability and cooling characteristics. In particular, during normal reactor operation, reducing the power of the circulation pump that sends the coolant to the fuel assembly, that is, improving the pressure loss characteristics of the fuel spacers, directly leads to the improvement of the power generation efficiency of the plant, thus reducing the spacer pressure loss. Such a proposal has been made conventionally.

By the way, in the case of a lattice type nuclear fuel spacer (not shown), a member at the center of the fuel rod space having a high flow velocity is projected in a mountain shape in the flow direction of the coolant, so that the flow passage area is rapidly changed by the spacer member. To reduce flow resistance and reduce spacer pressure loss.

In addition, as a method of reducing the flow resistance of the spacer, the flow resistance can be reduced by thinning the spacer member or by partially removing the member to reduce the spacer member projected area in the direction perpendicular to the coolant flow. There is an example in which

As described above, the device for reducing the spacer pressure loss has been devised. However, in the round cell type nuclear fuel spacer, the spacer is formed by circumscribing a cylindrical cell having a constant diameter corresponding to the fuel rod pitch. , The spacer member cannot be brought close to the vicinity of the fuel rod where the steam velocity is low.

Further, in the cell disclosed in Japanese Patent Publication No. 3-035640, not only must the shape be changed when the continuous loop spring installed in the cell is mounted, but also the stroke of the spring cannot be secured sufficiently. It will cause the trouble of. In the lattice spacer with protrusions, the effect of reducing pressure loss is remarkable even when compared with other spacers including the round cell type and the lattice type due to the relaxation of the flow passage area change rate due to the protrusions.

However, since the member is located in the center of the fuel rod space where the flow velocity of steam is highest, there is room for low pressure loss. As described above, there is a problem in that the conventional nuclear fuel spacer that reduces the flow resistance cannot obtain a sufficient pressure loss reduction effect.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a nuclear fuel spacer having a reduced flow resistance and a low pressure loss.

[0024]

A first aspect of the present invention is a cell type which includes a spacer band and a plurality of cylindrical cells arranged in the spacer band, and which supports a plurality of fuel rods arranged in a grid pattern. In the nuclear fuel spacer, the curvature of the remaining cell body excluding the circumscribing portion of one of the cells and the adjacent other cell is smaller than 1/2 of the fuel rod pitch,
In addition, the circumscribed portion with the adjacent cell has a cell projection portion obtained by plastically deforming the cell so as to project outward over the entire cell length.

A second aspect of the present invention is a cell-type nuclear fuel spacer that includes a spacer band and a plurality of cylindrical cells arranged in the spacer band, and supports a plurality of fuel rods arranged in a grid pattern. The cell circumscribed portion is longer than the length of the cell body of the cell, and has a protrusion protruding from both ends of the cell circumscribed portion in parallel with the flow of the coolant, and the protrusion has a joint surface with an adjacent cell. It is characterized in that the apex is formed so that the area of a cross section perpendicular to the flow of the coolant smoothly decreases toward the tip of the projection.

A third aspect of the present invention is a cell-type nuclear fuel spacer that includes a spacer band and a plurality of cylindrical cells arranged in the spacer band, and supports a plurality of fuel rods arranged in a grid pattern. It is characterized in that the outer diameter of the cell body is formed non-uniformly.

[0027]

The nuclear fuel spacer of the present invention has a cell shape in which only the joints between the cells project, and the cell members other than the joints can be brought close to the fuel rods until they come into close contact.

As shown in FIGS. 5 (a) and 5 (b), the cell member can be positioned near the fuel rod having a slow vapor velocity. If the vapor velocity impinging on the spacer member becomes slow, the flow resistance of the spacer decreases due to the above-mentioned relationship between the flow resistance R and the flow velocity V, and the pressure loss of the spacer can be reduced.

Further, by reducing the diameter of the cell, the projected area of the cell member can be reduced by about 10% and the pressure loss can be further reduced. On the other hand, there is a concern that the flow of vapor and liquid film near the fuel rod will be stagnant as the cell diameter becomes smaller, but the average thickness of the liquid film on the surface is about 0.2 to 0.6 mm. Even if the gap is narrower than that of the cell-type nuclear fuel spacer, it can sufficiently pass through.

As shown in FIG. 5B, the flow path wall (fuel rod)
The gas phase passes through the cell-fuel rod gap even if the distance between the fuel cell and the obstacle (spacer) is about 0.75 mm, and the coolant is blocked even if the cell is brought closer to the fuel rod surface than the current spacer. However, it can be seen that the cooling performance is not significantly impaired.

The circumscribed portion located in the narrowest portion of the fuel rod gap overlaps members and the elastic support portion is arranged, so that the spacer blocks the flow passage area. By providing the mold protrusions, the change in the coolant flow passage area when flowing into and out of the spacer is mitigated, thereby suppressing an increase in pressure loss.

Further, the inner surface of the coolant upstream end of the spacer cell is tapered so that a liquid film thicker than the gap between the spacer cell and the fuel rod is taken into the fuel rod side.

[0033]

EXAMPLE A first example of a nuclear fuel spacer according to the present invention will be described with reference to FIGS. In the figure, the same parts as those in FIG. 16 are designated by the same reference numerals. FIG. 2 is an enlarged view of a main part in FIG.

In FIG. 1, inconel tubular cells 24 are arranged in a spacer band 8 in a grid pattern of 8 rows and 8 columns. However, the central part where the water rod 7 is inserted is 4
It has been deleted.

As shown in FIG. 2, the tubular cell 24 has four outer contact portions 25 projecting outwardly evenly formed on the cell body 34 thereof, and an inward direction for supporting the fuel rod 2 is formed. Two fixed support portions 26 projecting inward are formed between the circumscribed portions 25, 25, and one elastic support portion 27 is further provided.

The curvature R of the cell body portion 34 of the tubular cell 24 is 1 / the pitch P between the fuel rods 2 and 2 as indicated by the broken line 28 in FIG.
2 is smaller than 2, and in the circumscribed portion 25, the cell protrusions 29 are formed by plastic deformation over the entire length of the cell body 34 of the tubular cell 24 as shown in FIGS. The cell projection 29 has a sharp tip, and the inner surface of the cylindrical cell 24 upstream of the coolant is tapered 31.

The spacer band 8 is, for example, a strip-shaped rectangular frame, and the spacer band 8 is provided with two spacer tabs 17 on each surface for ensuring a clearance between the channel box and the spacer.

Next, the operation of the above embodiment will be described. In this embodiment, the spacer member is close to the fuel rod 2, and no member is present in the center between the fuel portions 2 and 2. On the other hand, in the lattice type nuclear fuel spacer 5 of the conventional example shown in FIGS. 15 (a) and 15 (b), the intersection of the members is located at the center of the space of the fuel rod 2.

In the flow of the coolant in the fuel assembly, steam flows at high speed between the fuel rods, and water has an average thickness of 0.2 mm on the surface of the fuel rods.
It flows as a thin liquid film of about 0.6 mm. As shown in FIGS. 5A and 5B, the vapor flow velocity in the fuel rod space is such that the flow velocity is the slowest on the fuel rod surface and the highest in the fuel rod space center.

FIG. 5 (b) is a research report in which the flow velocity distribution in the radial direction in the rectangular channel was measured by flowing air at room temperature and normal pressure.
Air is passed through the rectangular cross section to measure the flow velocity distribution inside the flow passage, and the flow velocity distribution when there is no obstacle in the flow passage is indicated by the solid line, and the flow velocity distribution when a plate-like obstacle is placed parallel to the flow Is indicated by a symbol such as a circle.

Taking the case where there is no obstacle in the flow path as an example, the flow velocity is slow on the wall surface (y = 0) as indicated by the solid line. Flow resistance R is expressed by normal 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 flow Squares resistance.

Therefore, the fuel rod 2 having the highest vapor velocity is
In the round-cell type nuclear fuel spacer 14 having no spacer member in the center of the space, since the vapor near the fuel rod having a slow flow velocity collides with the spacer member, compared with the lattice type nuclear fuel spacer 5 having the spacer member in the center of the fuel rod space, The resistance decreases.

FIG. 5 (b) is quoted from Fukano et al., “Effect of obstacles on the flow of thin water film flowing with high-speed air flow”, multiphase flow, 3.4. (1989) p389-p404. It was done.

The flow of the coolant during the operation of a boiling water reactor (BWR) is such that there is a liquid film flow on the surface of the fuel rod and steam flows in the fuel rod space. The maximum thickness of the liquid film is about 1 to 2 mm, but on average it is a thin liquid film of about 0.2 mm to 0.6 mm (the minimum thickness is several tens of μm).

Therefore, the distance y between the fuel rods 2 and the spacer cells is approximately equivalent to that of the conventional round cell type nuclear fuel spacer 14.
Even if the distance from about 1.5 mm to about 0.75 mm, which is half of the distance, is approached, the coolant liquid film is not blocked at the inlet of the cell body 34, and the cooling performance of the fuel rod is not significantly deteriorated.

Although different from the BWR condition, the air-water experiment (FIG. 5 (b)) shows that the air flow passes to the same extent as when there is no spacer member even when brought close to 0.75 mm. Therefore, the liquid film that has flowed into the tubular cell 24 of this embodiment is also pulled by the vapor and flows, and the fuel film can be sufficiently cooled in the tubular cell 24 without the liquid film remaining behind.

On the other hand, the vapor colliding with the cell body 34 is shown in FIG.
As shown in (a), the velocity distribution is such that the velocity becomes maximum at the center of the fuel rod space and becomes almost equal to the velocity of the liquid film flow on the surface of the liquid film.

In FIG. 5 (a), reference numeral 5 is an example of a lattice type nuclear fuel spacer cell, 15 is a round cell type nuclear fuel spacer tubular cell, and 24 is a tubular cell in the embodiment of the present invention. There is. When the fuel portion pitch is P, the relation of ya = √2P / 2 yb = P / 2 yc <P / 2 is satisfied.

Incidentally, the vapor velocity near the outlet of the fuel assembly during rated operation is about 12 m / s, the moving velocity of the liquid film surface about 5 mm away from it is about 2 to 3 m / s, and its velocity distribution is It rapidly decreases as it approaches the film surface.

The flow resistance R is usually R = (resistance coefficient C _D ) ×
(The projected area to the plane perpendicular to the flow S) × (density of fluid [rho) × (the speed V of the fluid) is expressed by ^2/2. Therefore, since the flow velocity V squares on the flow resistance, the pressure loss reduction effect is great.

Further, if the cell material is made of Inconel and the material strength is made higher than that of zircaloy which is the material of the conventional spacer to reduce the wall thickness, the projected area of the spacer can be reduced, so that the pressure loss can be further reduced.

Zircaloy, which has excellent neutron economy as well as the conventional one, is used as the material. Even if the cell thickness is the same as the conventional one, the projected area can be reduced by about 10% due to the size effect of reducing the outer diameter of the cell. In the case of using Inconel and further reducing the cell thickness, the projected area can be reduced by more than 10%, and the flow resistance of the spacer can be greatly reduced together with the reduction of the flow velocity of the impinging vapor due to the reduction of the diameter of the cell body 34.

In the circumscribing portion 25 located at the narrowest portion of the fuel rod gap, members overlap and elastic supporting portions are arranged, which causes a large projected area of the spacer and causes a pressure loss increase. By providing a mountain-shaped protrusion on 25, the change in the coolant flow passage area is alleviated, and the change in the flow is moderated to suppress an increase in pressure loss.

Further, by forming the elastic support portion on the circumscribed portion 25 by plastic deformation, the cross-sectional area of the spacer can be reduced as compared with the case where the elastic member and the cell are made of different materials.

As shown in FIG. 6 (a), the outer diameter of the tubular cell 24 is reduced so that it is close to the outer diameter of the fuel rod 2 so that the liquid film 30 flowing on the surface of the fuel rod 2 while undulating. Cylindrical cell
The fuel rod 2 in the cylindrical cell 24 of the spacer is peeled off by the member of 24
In order to prevent the spacers from being used for cooling, the inner surface of the coolant upstream end of the cylindrical cell 24 of the spacer is tapered 31.

By this taper processing 31, the wave of the liquid film 30 thicker than the gap between the tubular cell 24 and the fuel rod 2 is cut, but originally, the flow passage area is reduced by the spacer member in the spacer cell. Therefore, even if the liquid film flow rate decreases, the cooling performance is higher than that of the assembly tube bundle part without spacers as long as the vapor flow rate increases and the liquid film flow rate increases accordingly. The cooling performance in the tubular cell 24 does not limit the limit output of the fuel assembly. Note that FIG. 6B shows a metal tubular cell 15 of the conventional round cell type nuclear fuel spacer 14 in comparison.

FIG. 7 (a) shows a state in which the tubular cell 24 of this embodiment is connected to an adjacent tubular cell 24 by a loop spring 32, and FIG. 7 (b) shows a conventional Japanese Patent Publication No. 3-035640. The round cell 18 described in the publication is shown in contrast.

As is apparent from both of these figures, the loop spring 32 connecting the fuel rod 2 and the tubular cell 24 or the round cell 18 can be a lantern type with the central portion protruding in FIG. 7 (a). While the spring stroke 33 can be increased,
In FIG. 7B, the spring stroke 33 is small because it is cylindrical.

Therefore, in this embodiment, the distance between the fuel rod 2 and the tubular cell 24 can be increased, and the pressure loss of the spacer can be reduced.

Next, another example of the cell body 34 of the tubular cell 24 in the round cell type nuclear fuel spacer shown in the first embodiment will be described with reference to FIGS. 8 to 13. The same parts as those in FIGS. 2 to 4 are designated by the same reference numerals, and the description of the overlapping parts will be omitted. Only the different parts will be described.

FIG. 8 shows the cell body 34 which constitutes the fuel spacer.
Has an uneven outer diameter. FIG. 9 shows an example in which the protruding heights of the circumscribing portions 25 of the cell body 34 of the tubular cell 24 are different in the cell circumferential direction. For example, when supporting a fuel assembly with an uneven pitch arrangement, cells with a large diameter are arranged in a portion with a large spacer pitch to form an uneven pitch spacer in which the height of the circumscribing protrusion is constant, or conversely. A spacer for non-uniform pitch can be constructed by changing the protruding height of the circumscribing portion while keeping the cell diameter constant.

Further, the relative output in the fuel assembly is large in accordance with the output distribution of the fuel assembly, and the diameter of the cell body 34 is increased so that the liquid film is not easily separated by the cells in the fuel rod 2 which is thermally severe. It is possible to reduce the pressure loss of the fuel assembly and suppress the lowering of the limit output by adopting the spacer configuration in which the height of the circumscribed portion is reduced.

In particular, in the case of a high burnup fuel that has improved fuel economy, due to the nuclear design, there is a tendency that high power fuel rods are arranged at the outermost periphery of the fuel assembly and the fuel rods in the second row, and become thermally strict. is there.

In this case, by using a fuel spacer having a small outer diameter of the cell body in the outermost periphery of the fuel assembly and in the third column rather than the second column, it is possible to suppress the thermal power from severely lowering the limit output of the fuel rod. It is possible to reduce the outer diameter of the fuel rod having a small relative output inside the assembly to enhance the pressure loss reduction effect, suppress the limit output reduction, and reduce the pressure loss.

FIG. 10 shows a window 35 in the cell body 34 excluding the circumscribing portion 25.
Is provided to further reduce the pressure loss at the cell body 34. In the case of a cylindrical round cell, if the cell body portion 34 is similarly thinned out, only a thin plate-like portion remains in the cell body portion 34, and a decrease in strength cannot be avoided.

On the other hand, in the cylindrical cell of the spacer of this embodiment, since the circumscribing portion 25 is plastically deformed into a U-shape, the bending rigidity is high, and the cell strength after thinning is a circular tubular round cell. Has the effect of increasing compared to.

In FIG. 11, as in FIG. 10, a window 35 is provided in the cell body 34, and both ends of the remaining cell are plastically deformed, and a plurality of fixed elastic support portions 36 are provided in the circumferential direction of the cell body 34. As an example, Figure 12
Is a plan view of the cell body 34, and FIG. 13 is a sectional view of the cell body 34 taken along the line AA. The fixed elastic support portion 36 in FIG. 12 also serves as elastic support for supporting the fuel rod in the elastic deformation range.

In order to make the insertion of the fuel rod smooth, the fixed elastic support portion 36 of the fuel rod has a dogleg shape as shown in FIG. The height δ of the dogleg is set to be larger than the displacement of the elastic deformation of the fixed elastic support portion 36.

Further, the circumscribed portion 25 and the circumscribed portion of the cell body 34
By providing at least one fixed elastic support portion 36 in the portion sandwiched by 25 and 25, the distance between the members of the fuel rod 2 and the cell body 34 is biased, and the liquid film flow is in the circumferential direction of the cell body 34. It is designed to keep the distance even so that there is no local stagnation.

In the structure shown in FIG. 3, the circumscribed portion 25 of the tubular cell 24 is formed to have the same length as the cell body 34,
A taper process 31 can be applied to the inner surface side of the cell body portion 34 of the circumscribed portion 25. When formed in this way, the circumscribed portion 25
As in the case where the protrusion is provided on the substrate, it has the effect of alleviating the change in the cross-sectional area of the spacer member.

Next, the embodiments of the nuclear fuel spacer according to the present invention will be summarized and listed below. (1) A plurality of elongated fuel rods installed in the fuel assembly,
A nuclear fuel spacer for holding a moderator tube and other components in a predetermined lateral position.In a cell-type nuclear fuel spacer formed by circumscribing a tubular cell surrounding a fuel rod, the circumscribing portion with the adjacent cell is The curvature of the remaining cell body is less than 1/2 of the fuel rod pitch, and the circumscribing portion with the adjacent cells plastically deforms the tubular cell so that it projects outward over the entire cell length. Formed.

(2) The length of the circumscribed portion is longer than the length of the cell body, both ends of the circumscribed portion of the cylindrical cell project in parallel with the flow of the coolant, and the protrusion is It should be finished so that the area of the cross section perpendicular to the flow of the coolant decreases smoothly toward the tip of the protrusion, with the joint surface between adjacent cylindrical cells as the apex.

(3) The inner surface of the coolant upstream end of the spacer cell is tapered. (4) The outer diameter of the cell body of the tubular cell forming the fuel spacer is not uniform. (5) Of the multiple cylindrical cells that make up the nuclear fuel spacer,
The outer diameter of the cell body within the third row is smaller than the outer diameter of the outermost circumference of the fuel assembly and the cell body of the tubular cells in the second row.

(6) The protruding height of the circumscribed portion in the direction perpendicular to the flow is different in the circumferential direction of the tubular cell. (7) An elastic support portion formed by plastically deforming the tubular cell is provided at one or more places of the circumscribed portion.

(8) A window is provided in the cell body except for the circumscribed portion, and a fixed elastic support portion obtained by plastically deforming the tubular cell is provided in a portion near both ends of the tubular cell in the circumferential direction of the cell. A plurality of fixed elastic support portions are provided to support the fuel rods by elastic deformation of the cells.

(9) At least one fixed elastic support portion is provided in the portion sandwiched between the circumscribed portion of the cell body and the other circumscribed portion. (10) The length of the circumscribed portion and the length of the cell body are the same,
In addition, the inside of both ends of the cell in the circumscribing part must be tapered.

[0077]

According to the present invention, the spacer member can be arranged in the vicinity of the fuel rod having a low vapor velocity in the fuel rod space, the vapor velocity colliding with the spacer member can be reduced, and the radius of the cell body can be reduced. The projected area of the spacer in the plane perpendicular to the flow can be reduced. Due to the synergistic effect of the reduction of the impinging vapor velocity and the reduction of the projected area, the flow resistance can be reduced and a nuclear fuel spacer with a low pressure loss can be obtained.

Further, since the outer diameter of the spacer cell and the diameter of the spacer body can be set independently, it is easy to adapt the fuel assembly having a non-uniform fuel rod pitch. Further, by appropriately selecting the cell body diameter according to the output distribution of the fuel assembly, it is possible to reduce the influence on the cooling of the fuel assembly and reduce the pressure loss.

[Brief description of drawings]

FIG. 1 is a plan view showing a first embodiment of a nuclear fuel spacer according to the present invention.

FIG. 2 is an enlarged plan view showing a main part of FIG.

FIG. 3 is an elevation view showing a direction of arrow AA in FIG.

4 is an enlarged schematic view of a circumscribed portion of the cell in FIG.

FIG. 5 (a) is a schematic diagram showing a comparison of vapor velocity distributions near fuel rods of a nuclear fuel spacer of the present invention and a conventional example, and FIG. 5 (b).
Is an air flow velocity distribution diagram showing a case where a plate-shaped obstacle is placed in a rectangular flow path and a case where it is not placed.

FIG. 6 is a side view showing the relationship between a fuel rod, a liquid film, a vapor velocity distribution, and a spacer member, (a) showing an embodiment of the present invention,
(B) shows a conventional example, respectively.

FIG. 7 is a vertical cross-sectional view showing a partial side view of a spring stroke of a fuel rod and a cell, (a) showing an embodiment of the present invention and (b) showing a conventional example.

FIG. 8 is a plan view showing an arrangement example of cells in which the diameter of the cell body of the nuclear fuel spacer in FIG. 1 is different.

9 is a plan view showing an arrangement of cells having different circumscribed portion heights in FIG. 8. FIG.

10 is a sketch drawing showing a cell in which the cell body of the nuclear fuel spacer in FIG. 1 is lightened to provide a window. FIG.

FIG. 11 is a sketch drawing showing a cell in which a fixed support portion also serves as an elastic support portion in FIG.

FIG. 12 is a plan view of FIG.

FIG. 13 is a vertical cross-sectional view taken along the line AA in FIG.

FIG. 14 is an elevational view showing a partial cross section of a fuel assembly for a boiling water reactor.

15A is a plan view showing a conventional lattice type nuclear fuel spacer used in FIG. 14, and FIG. 15B is a side view showing a partial cross section of FIG.

16 is a plan view showing a conventional round cell type nuclear fuel spacer used in FIG.

FIG. 17 is a plan view showing an enlarged main part in FIG.

18 (a) is a plan view showing another example of a cell of a conventional round cell type nuclear fuel spacer, and FIG. 18 (b) is a side view of FIG. 18 (a).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... BWR fuel assembly, 2 ... Fuel rod, 3 ... Upper tie plate, 4 ... Lower tie plate, 5 ... Lattice type nuclear fuel spacer, 6 ... Channel box, 7 ... Water rod, 8
... Spacer band, 9 ... Lattice plate, 10 ... Square partition space, 11 ... Fixed support part, 12 ... Elastic support member, 13 ... Leaf-like protrusion, 14 ... Round cell type nuclear fuel spacer, 15 ... Metal tubular cell, 16 ... Leaf spring, 17 ... spacer tab, 18 ... round cell, 19
... upper end, 20 ... lower end, 21 ... main body, 22 ... gap,
23 ... circumscribed portion, 24 ... tubular cell, 25 ... circumscribed portion, 26 ... fixed support portion, 27 ... elastic support portion, 28 ... broken line, 29 ... cell projection portion, 30
… Liquid film, 31… Tapering, 32… Loop spring, 33… Spring stroke, 34… Cell body, 35… Window, 36… Fixed elastic support.

Claims (3)

[Claims] 1. A cell-type nuclear fuel spacer comprising a spacer band and a plurality of tubular cells arranged in the spacer band, and supporting a plurality of fuel rods arranged in a lattice, wherein one of the cells is The curvature of the remaining cell body excluding the circumscribed portion with the other adjacent cell is less than 1/2 of the fuel rod pitch, and the circumscribed portion with the adjacent cell extends the cell over the entire length of the cell. A nuclear fuel spacer having a cell protrusion that is plastically deformed so as to protrude to the outside. 2. A cell-type nuclear fuel spacer comprising a spacer band and a plurality of cylindrical cells arranged in the spacer band, and supporting a plurality of fuel rods arranged in a grid pattern, wherein the cell shell of the cell is The cell circumscribing portion is longer than the length of the portion, and has a protruding portion projecting both ends of the cell circumscribing portion in parallel with the flow of the coolant, and this protruding portion has a junction surface with an adjacent cell as an apex, A nuclear fuel spacer, characterized in that the area of a cross section perpendicular to the flow of the coolant is formed so as to decrease smoothly toward the tip of the protrusion. 3. A cell-type nuclear fuel spacer comprising a spacer band and a plurality of tubular cells arranged in the spacer band and supporting a plurality of fuel rods arranged in a grid pattern, wherein the cell shell of the cell is A nuclear fuel spacer having a non-uniform outer diameter.