JPH03142398A - Fuel assembly - Google Patents

Abstract

PURPOSE:To reduce the pressure loss of a fuel spacer to increase a thermal margin by providing a cylinder member with projections and elastic members which supports fuel rods and forming passages of a refrigerant in the axial direction. CONSTITUTION:A fuel spacer 14 has circular cells 13 arranged in a lattice, and the cell 13 has plural rigid projecting parts 15 and elastic members 16 which support a fuel rod inserted into the cell 13. Members 16 are attached to the cell 13 and project into adjacent cells 13. The passage for the refrigerant is formed in the axial direction of the cell 13 by projecting parts 15 and cells 13. Vacant holes 21 are formed in diagonal directions of the lattice arrangement of the cell 13. The projection area in the axial direction of the fuel rod 1 of projecting parts 15 is small and the pressure loss of the spacer 14 is reduced. The refrigerant is not stirred between fuel rods 1 adjacent in diagonal directions by forming vacant holes 21, and the thermal margin is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel assembly, and particularly to a fuel assembly suitable for use in a boiling water nuclear reactor.

FIG. 1 shows a schematic structure of a fuel assembly conventionally used in a boiling water nuclear reactor. 1 is a fuel rod, 2 is a fuel spacer that maintains the horizontal distance between the plurality of fuel rods 1 at a predetermined width, and 3 is a fuel spacer that maintains the vertical distance between the plurality of fuel spacers 2 arranged in the axial direction at a predetermined width. Spacer support rods 4 and 5 are an upper tie plate and a lower tie plate that support both ends of each fuel rod 1 and spacer support rod 3. The fuel spacer 2 is supported by a protrusion 6 provided on the spacer support rod 3.

A schematic structure of the fuel spacer 2 is shown in FIG.

The fuel spacer 2 includes a depider 7 assembled in a grid shape.
and 8 and pars 19 and 20, a lantern box 9 provided at the intersection of pars 19 and 20, a lantern spring 10 provided in the lantern box 9, and a divider 7
and S-bend 11 provided at 8. and a band 12 constituting the outer periphery.

Fuel spacer 2 is attached to lantern box 9 and S pend 1
1, the projected area in the axial direction of the fuel rod becomes considerably large, resulting in a large pressure loss. Furthermore, the fuel spacer 2 is susceptible to output fluctuations caused by control rod operation because the coolant flowing inside the fuel assembly is stirred at the intersections of the divider 7, the divider 8, and the par 20, and the intersection of the divider 8 and the par 19. Film boiling occurs on the surface of the fuel rods in the vicinity of the fuel assembly where it is easy to occur. Therefore, it has not been possible to improve the minimum value of the ratio of the critical power to the power of the fuel assembly during nuclear reactor operation (referred to as minimum critical power ratio, MCPR).

Improvements are desired in improved boiling water reactors from the viewpoints of core safety and thermal-hydraulic characteristics.

An object of the invention of this application is to provide a fuel assembly that can reduce pressure loss in fuel spacers and increase thermal margin.

A feature of the invention of this application is that the fuel spacer includes a plurality of cylindrical members arranged in a lattice pattern, and the cylindrical member hits a plurality of protrusions that support the fuel rods inserted therein, and the fuel spacer l1III supporting the fuel rods inserted into the member
The forest member is attached to the cylindrical member and protrudes into each of the adjacent cylindrical members, a passage through which a coolant passes in the axial direction of the cylindrical member is formed by the protrusion and the cylindrical member, and the cylindrical member Holes are formed between the diagonally adjacent cylindrical members arranged in a grid pattern. According to this feature, the protrusion that supports the fuel rods and the dispensing member are provided on the cylindrical member, and the passage through which the coolant passes in the axial direction of the cylindrical member is formed between the protrusion and the cylindrical member. By reducing the projected area of the fuel spacer in the axial direction, the pressure loss of the fuel spacer can be reduced. Furthermore, since holes are formed between a plurality of diagonally adjacent cylindrical members in the lattice-like arrangement of cylindrical members, thermal margin, that is, MC
PR can be improved.

A fuel assembly which is a preferred embodiment of the present invention applied to a boiling water nuclear reactor will be explained with reference to FIGS. 3 to 6. These drawings show the fuel spacer used in this example. The other structure of this embodiment is the same as the structure of FIG. Therefore, the configuration of the fuel spacer will be explained.

The fuel spacer 14 used in this embodiment has a large number of independent circular cells 13 arranged adjacent to each other in a grid pattern, and a band surrounds the outermost circular cell 13. Adjacent circular cells 13 are joined to each other. Each circular cell 13 has rigid protrusions 15 provided at two locations in the circumferential direction. Rigid protrusion 1
5 protrudes into the circular cell 13. Rigid protrusion 15
is constructed by making a notch in the side wall of the circular cell 13 and extruding a part of the side wall inward.

Therefore, as shown in FIGS. 3 and 4, the circular cell 1
An opening 26 in the fuel rod axial direction, that is, a passage through which cooling water passes in the axial direction, is formed between the side wall 3 and the rigid protrusion 15. The elastic support portion 16 is made of a cylindrical circular elastic body, and is attached across adjacent circular cells 13 . That is, as the circular cell 13, two types of circular cells 13a and 13b shown in FIGS. 5 and 6 are used.

The circular cell 13a has a U-shaped slit 16a in the axial center of the side wall, and the circular cell 13b has a rectangular slit 16b in the axial center of the side wall. Elastic support part 1
6, a part of the elastic support part 16 is inserted and attached into the opposing U-shaped slit 16a and rectangular slit 16b of the adjacent circular cells 13a and 13b, as shown in FIG. A portion protrudes into the circular cell 13a and another portion protrudes into the circular cell 13b.

As shown in FIG.
The circular cell 13a is inserted into the slit of 3b.
The upper and lower ends of and 13b are joined by welding.

The fuel assembly of this embodiment has a rigid protrusion 15 (structure having an opening 26) with a smaller projected area in the fuel rod axial direction than the conventional S-bend 11, and also has a lantern box like the fuel spacer 2. 9, the projected area of the fuel rod in the axial direction is significantly reduced compared to the conventional one. Therefore, the pressure loss of the fuel spacer 14 used in this embodiment is significantly lower than that of the conventional fuel spacer 2.

Since the elastic support portion 16 has an opening in the fuel rod axial direction like the rigid protrusion 15, the projected area of the fuel spacer 14 in the fuel rod axial direction is further reduced, and the fuel spacer 1
The pressure loss of No. 4 can be further reduced.

Since the fuel assembly of this embodiment uses circular cells 13, the holes 21 are diagonally arranged as shown in FIG. 3 instead of the lattice intersections 22 (FIG. Since it is formed between adjacent fuel rods, stirring of the coolant does not occur between diagonally adjacent fuel rods.Therefore, the fuel rods in the part where the output fluctuation is large near the control rod part around the fuel assembly The occurrence of film boiling on the surface is suppressed, and the MCPR of the fuel assembly is improved.Therefore, in this embodiment, the core stability is improved and the thermal-hydraulic characteristics are improved.

The rigid protrusion 15 may be provided at the position shown in FIG. That is, the rigid protrusion 15 is provided at the axial center of the circular cells 13a and 13b. As in the case of FIG. 4, an opening 26 is formed by the circular cell 13a (circular cell 13b) and the rigid protrusion 15.

Other embodiments of the fuel spacer 14 will be described below. In the fuel spacer of this embodiment, all of the circular cells 13 are formed into circular cells 13 having U-shaped slits 16a as shown in FIG.
A, two of these circular cells 13a are combined upside down, and a circular elastic body constituting one elastic support part 16 is attached in each slit to form the circular cells 13a.
The upper and lower ends of the two are joined by welding (Fig. 8). In the fuel spacer of this embodiment, the circular cell 16 is the circular cell 13.
Only one type of fuel spacer a is required, and manufacturing is easier than with the fuel spacer 14 described above.

Another embodiment of the fuel assembly of the present invention will be described with reference to FIG. The fuel assembly of this embodiment has a spacer support rod 17
and a fuel spacer 23. This fuel spacer 23 has a large number of circular cells 13 like the fuel spacer 14.
are arranged in a grid pattern, and further includes a circular elastic support member 18.

In detail, the circular cell 13 is connected to the spacer support rod 1
They are arranged in a grid pattern except for the part where number 7 is arranged.

The circular elastic support member 18 has a cylindrical shape, similar to the elastic support section 16 that is made of a cylindrical circular elastic body. In the fuel assembly of this embodiment, two spacer support rods 17 are inserted into a gap formed by being surrounded by a plurality of circular cells 13. This gap is formed by the fuel spacer 23
It is a space in which a circular cell 13 can be placed.

In a fuel spacer using circular cells 13, circular cells 13
With the spacer support rod inserted inside, the protrusion 6 of the spacer support rod is inserted in the same manner as the fuel spacer 2 in FIG.
The fuel spacer is attached to the spacer support rod by inserting the protrusion 6 into the square with the fuel spacer 2 facing the same direction. It cannot be locked. This is because the radial length of the protrusion that supports the fuel spacer cannot be increased because the spacer support rod is inserted into the circular cell. In this embodiment, a spacer support rod 17 is inserted into a gap formed by being surrounded by a plurality of circular cells 13, and a circular elastic support member is inserted between circular cells 13 adjacent to this spacer support rod 17. 18 and attaching it to the circular cell 13 solves the above problem. It can be said that the circular elastic support member 18 is installed across two adjacent circular cells 13. Furthermore, a circular elastic support member 18 is supported by a protrusion 6 provided on one spacer support rod 17.

The gap into which the one spacer support rod 17 described above is inserted is formed by removing one circular cell 13. It can be said that this gap determines the area in which the circular cell 13 can be arranged. The circular cell 13 adjacent to each spacer support rod 17, for example circular cell 13c, has an outwardly projecting rigid support member 15a. In this embodiment, the smooth support rod 17 is supported at three points by three support members such as the rigid support member 15a and the circular elastic support member 18 in the direction perpendicular to the axis of the fuel assembly, and The movement of the spacer support rod 17 is controlled at. A protrusion 6 is provided on the side surface of one spacer support rod 17 similarly to the spacer support rod 3. This projection 6 appropriately holds the fuel spacer 23 in a predetermined position in the axial direction.

When inserting the spacer support rod 17 into the gap of the fuel spacer 23, first, the protrusion 6 is positioned in the recess formed between the circular elastic support member 18 and the adjacent circular cell 13 ( After inserting the protrusion 6 into the recess at the position 6' in FIG. It is locked to the elastic support member 18. By this operation, the spacer support rod 17 is inserted into the gap of the fuel spacer 23, and the protrusion 4 supports the lower surface of the circular n+h support member 18.

Spacer support rod 17 in a direction perpendicular to the axis of the fuel assembly
By making one support member (for example, the circular elastic support member 18) an elastic support member among the three support members supporting the fuel spacer 23, the spacer support rod 17 can be easily inserted into the gap of the fuel spacer 23. This is an application of the concept of the conventional fuel spacer shown in FIG.

That is, even in this conventional fuel spacer, one of the three supporting members is the lantern spring 10 which is an elastic body.
This facilitates insertion of the spacer support rod 6. The locking operation of the projection 6 to the circular elastic support member 18 can also be performed as follows. That is, the protrusion 6 is positioned in the recess 27 between two circular cells 13 that are adjacent to the spacer support rod 17 and further adjacent to each other, and in this state, the protrusion 6 is moved to the opposite side of the circular elastic support member 18. In this method, the spacer support rod 17 is rotated so that the projection 6 comes to the position of the circular elastic support member 18.

In the fuel assembly of this embodiment, the pressure loss of the fuel spacer is reduced and the MCPR of the fuel assembly is improved as in the embodiment of FIG. 3. Therefore, in this embodiment as well, the core stability is improved and the thermal-hydraulic characteristics are improved. Moreover, in the fuel assembly of this embodiment, the circular elastic support member 18 is supported by the protrusion 6;
That is, since the fuel spacer 23 can be easily supported by rotating the spacer support rod 17, the fuel spacer 23 can be easily supported.
can be easily supported by the spacer support rod 17. Further, since the spacer support rod 17 is inserted into the gap surrounded by the plurality of circular cells 13 outside the circular cell 13, the outer diameter of the spacer support rod 17 can be made larger than the outer diameter of the fuel rod 1.

As the spacer support rod 17, for example,
No. 139892, Japanese Patent Application Laid-open No. 1983-72388,
JP-A-55-83881, JP-A-55-9418
It is possible to use water rods having the function of supporting a fuel spacer as shown in Japanese Patent Application Laid-Open No. 56-106183 and Japanese Patent Application Laid-open No. 56-120976.

FIG. 10 shows a fuel assembly according to another embodiment of the present invention in which a fuel spacer 24 is used in place of the fuel spacer 23. The fuel assembly of this example differs from the fuel assembly of FIG. 9 only in the structure of the fuel spacer. In the fuel spacer 24 used in this embodiment, the circular elastic support member 18 of the fuel spacer 23 is replaced with a square elastic support member 25. The square elastic support member 25 has a cylindrical shape like the circular elastic support member 18. The spacer support rod 17 is supported at three points, two rigid support members 15a and a rectangular elastic support member 25, in a direction perpendicular to the axis of the fuel assembly.

The operation of locking the projection 6 of the spacer support rod 17 to the rectangular elastic support member 25 is performed as follows. That is, the protrusion 6 is located adjacent to the spacer support rod 17 and further adjacent to each other in the space 27 between the two circular cells 13.
In this state, the projection 6 is moved to the opposite side of the square elastic support member 25, and the spacer support rod 17 is rotated so that the projection 6 comes to the position of the square elastic support member 18. This embodiment can obtain the same effects as the embodiment shown in FIG. Furthermore, in this embodiment, since the engaging portion between the projection 6 and the square elastic support member 25 is large, the support of the fuel spacer 24 by the projection 6 during the reactor use period of the fuel assembly becomes more reliable. .

According to the features of the invention of this application, the pressure loss of the fuel spacer can be reduced by reducing the projected area of the fuel spacer in the axial direction, and furthermore, the pressure loss of the fuel spacer can be reduced by reducing the projected area of the fuel spacer in the axial direction. The thermal margin, ie, MCPR, can be improved by forming the pores.

[Brief explanation of the drawing]

Figure 1 is a partial vertical cross-sectional structural diagram of a conventional fuel assembly used in a boiling water reactor; Figure 2 is a plan view of a fuel spacer used in the fuel assembly shown in Figure 1; 3 is a plan view of a fuel spacer used in a fuel assembly that is a preferred embodiment of the present invention, FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. 3, and FIGS. 5 and 6 are views shown in FIG. circular cells 13a and 13
7 and 8 are longitudinal sectional views of another embodiment of the assembled state of the pair of circular cells shown in FIG. 4, and FIGS. 9 and 10 are side views of the fuel assembly of the present invention. FIG. 7 is a cross-sectional view of another embodiment. l...Fuel rod, 4...Upper tie plate, 5...
Lower tie plate, 13... circular cell, 14.23.
24...Fuel spacer, 15...Rigid protrusion, 16
... Elastic support part, 17 ... Spacer support rod, 1
8... Circular elastic support member, 21... Hole, 25...
...Square-shaped elastic support member. Figure Figure Figure 3 Figure Figure 5 5 Figure Figure Figure Figure 5 Figure

Claims (1)

[Claims] 1. A fuel assembly including a plurality of fuel rods and a fuel spacer that maintains a mutual spacing between the fuel rods, wherein the fuel spacer includes a plurality of cylindrical members arranged in a grid pattern. The cylindrical member has a plurality of protrusions that support the fuel rods inserted therein, and the elastic member that supports the fuel rods in the cylindrical member is attached to the cylindrical member and adjacent to the cylindrical member. A passage projecting into each of the cylindrical members and passing a coolant in the axial direction of the cylindrical member is formed by the protrusion and the cylindrical member, and a passage is formed between the cylinders adjacent to each other in the diagonal direction of the lattice arrangement of the cylindrical members. A fuel assembly characterized in that voids are formed between members. 2. The fuel assembly according to claim 1, wherein the protrusion is a part of the cylindrical member protruding inward. 3. The fuel assembly according to claim 1, wherein the elastic support portion has an opening facing in the axial direction of the cylindrical member.