JPH0512680B2 - - Google Patents

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
1 is a fuel rod, 2 is a fuel spacer that maintains a horizontal interval between a plurality of fuel rods 1 at a predetermined width, and 3 is a fuel spacer that maintains a vertical interval between a plurality of fuel spacers 2 arranged in an axial direction at a predetermined width. spacer support rod,
4 and 5 are each fuel rod 1 and spacer support rod 3
They are an upper tie plate and a lower tie plate that support both ends of the. The fuel spacer 2 is supported by a projection 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 dividers 7 and 8 and bars 19 and 20 assembled in a lattice shape, a lantern box 9 provided at the intersection of the bars 19 and 20, a lantern spring 10 provided in the lantern box 9, and the divider 7. and S provided in 8
It consists of a bend 11 and a band 12 that structures the outer periphery.

The fuel spacer 2 is connected to the lantern box 9 and S.
Due to the presence of the bend 11, the projected area of the fuel rod in the axial direction becomes considerably large, resulting in a large pressure loss. Furthermore, since the fuel spacer 2 causes agitation of the coolant flowing inside the fuel assembly at the intersections of the divider 7, the divider 8, and the bar 20, and the intersection of the divider 8 and the bar 19, the influence of output fluctuations due to control rod operation is reduced. Film boiling occurs on the surface of the fuel rods in the vicinity of the fuel assembly, which is susceptible to this. 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.

The invention of this application provides 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 is configured such that a part of the cylindrical member protrudes inward, and has a plurality of arcuate protrusions that support the fuel rods inserted therein, and supports the fuel rods within the cylindrical member. The elastic member is attached to the cylindrical member and protrudes into each of the adjacent cylindrical members, and the protrusion and the elastic member are provided at different heights in the axial direction of the cylindrical member. , a passage for passing a coolant in the axial direction of the cylindrical member is formed by the protrusion and the cylindrical member, and a hole is formed between the cylindrical members adjacent in the diagonal direction of the lattice arrangement of the cylindrical members. It's in being. According to this feature, the protrusion and the elastic member that support the fuel rods 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 direction, the pressure loss of the fuel spacer can be reduced. In addition, since holes are formed between a plurality of diagonally adjacent cylindrical members in the lattice arrangement of cylindrical members, thermal margin, i.e.
MCPR can be improved. Furthermore, since the protrusion and the elastic member are provided at different heights in the axial direction of the cylindrical member, the protrusion has an area that transmits the heat generated by the fuel rod to the coolant at the point of contact between the cylindrical member and the fuel rod. and the elastic member can be made larger than those provided at the same height in the axial direction of the cylindrical member, and as a result, thermal margin is improved. This result, combined with the effect of using a so-called circular cell, a cylindrical member that stirs the coolant and prevents the flow from being disturbed, produces an excellent thermal effect, as shown in Figure 2. It is possible to provide a fuel assembly having excellent effects that cannot be obtained when a protrusion and an elastic member are provided at the same height in the axial direction in a so-called square cell fuel spacer.

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 structure 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, with the outermost circular cell 1
A band surrounds the outside of 3. 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. The rigid protrusion 15 is
It 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, 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 of the circular cell 13 and the rigid protrusion 15. Ru. The elastic support portion 16 is made of a cylindrical circular elastic body, and is attached to span 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. As shown in FIG. 4, the elastic support portion 16 is formed by forming a U-shaped slit 16a and a rectangular slit 1 facing each other in adjacent circular cells 13a and 13b.
6b and is installed. Elastic support part 1
6, a part of which protrudes into the circular cell 13a, and another part of which protrudes into the circular cell 13b. As shown in FIG. 4, the upper and lower ends of the circular cells 13a and 13b are joined by welding with the elastic support portions 16 installed in the slits of the circular cells 13a and 13b.

The fuel assembly of this example is a conventional S-bend 11
It has a rigid protrusion 15 (structure with an opening 26) with a smaller projected area in the axial direction of the fuel rod than that of the fuel rod, and does not have a lantern box 9 like the fuel spacer 2, so the projected area in the axial direction of the fuel rod is The area is significantly smaller than before. Therefore, the pressure loss of the fuel spacer 14 used in this embodiment is
This is significantly lower than that of the conventional fuel spacer 2.

Since the elastic support portion 16 has an opening in the axial direction of the fuel rod like the rigid protrusion 15, the projected area of the fuel spacer 14 in the axial direction of the fuel rod is further reduced, and the pressure loss of the fuel spacer 14 is further reduced. Can be reduced.

Since the fuel assembly of this embodiment uses circular cells 13, lattice intersections such as fuel spacers 2
2 (FIG. 2), holes 21 are formed between diagonally adjacent fuel rods as shown in FIG. Does not occur. Therefore, the occurrence of film boiling on the surface of the fuel rods in the portion where the output fluctuation is large near the control rod insertion portion around the fuel assembly is suppressed, and the MCPR of the fuel assembly is improved. Therefore, in this embodiment, core stability is improved and thermal-hydraulic characteristics are improved.

Other embodiments of the fuel spacer 14 will be described below. In the fuel spacer of this embodiment, all the circular cells 13 are connected to the U-shaped slits 16a shown in FIG.
A circular cell 13a having
A circular elastic body constituting one elastic support part 16 is attached in each slit by combining two cells 13a upside down, and the upper and lower ends of the circular cells 13a are joined by welding. Figure 7). In the fuel spacer of this embodiment, only one type of circular cell 13a is sufficient as the circular cell 16, and the fuel spacer 14 described above
The structure is easier than that.

Another embodiment of the fuel assembly of the present invention will be described with reference to FIG. The fuel assembly of this embodiment includes a spacer support rod 17 and a fuel spacer 23. This fuel spacer 23 is similar to the fuel spacer 14
A large number of circular cells 13 are arranged in a lattice shape as shown in FIG. 1, and a circular elastic support member 18 is further provided.

Specifically, the circular cells 13 are arranged in a lattice pattern except where the spacer support rods 17 are arranged. The circular elastic support member 18 is the elastic support part 1 made of a cylindrical circular elastic body.
6, it has a cylindrical shape. In the fuel assembly of this embodiment, two spacer support rods 17 are inserted into a cavity formed by surrounding a plurality of circular cells 13. This empty space is the fuel spacer 23
It is a space in which a circular cell 13 can be placed.

In the case of a fuel spacer using circular cells 13, with the spacer support rods inserted into the circular cells 13, the same method as for the fuel spacer 2 shown in FIG. The protrusion 6 of the spacer support rod is inserted into the square with the protrusion 6 facing it, and then the spacer support rod is rotated 45 degrees to lock the protrusion 6 to the divider of the fuel spacer 2. The spacer cannot be engaged with the spacer support rod. This is because the radial length of the protrusion supporting the fuel spacer cannot be increased in relation to allowing the spacer support rod to penetrate into the circular cell. In this embodiment, a spacer support rod 1 is placed in a space surrounded by a plurality of circular cells 13.
7 and by placing a circular elastic support member 18 between the circular cells 13 adjacent to this spacer support rod 17 and attaching it to the circular cells 13. ing. It can be said that the circular elastic support member 18 is installed astride 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 cavity into which the aforementioned one spacer support rod 17 is inserted is formed by removing one circular cell 13. It can be said that this sky is large enough to accommodate the circular cell 13. 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 spacer support rod 17 is supported at three points by three support members such as a rigid support member 15a and a circular elastic support member 18 in a direction perpendicular to the axis of the fuel assembly. The movement of the spacer support rod 17 is controlled at the spacer support rod 17. A protrusion 6 is provided on the side surface of one spacer support rod 17 in the same way as the spacer support rod 3. This protrusion 6 properly holds the fuel spacer 23 in place in the axial direction.

When inserting the spacer support rod 17 into the cavity 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. (position 6' in FIG. 8) and insert the protrusion 6 into the recess, and after the protrusion 6 has moved to the opposite side of the circular elastic support member 18, rotate the spacer support rod 17 to rotate the protrusion 6 into a circular shape. It is locked to the shape elastic support member 18. By this operation, the spacer support rod 17 is inserted into the cavity of the fuel spacer 23, and the projection 6 supports the lower surface of the circular elastic support member 18.
By making one of the three support members (for example, the circular elastic support member 18) an elastic support member among the three support members that support the spacer support rod 17 in a direction perpendicular to the axis of the fuel assembly, the spacer support rod 17 can be Insertion of the fuel spacer 23 into the air becomes easier. This is an application of the concept of the conventional fuel spacer shown in FIG.

That is, even in this conventional fuel spacer, the spacer support rod 6 can be easily inserted by using the lantern spring 10, which is an elastic body, as one of the three support members. 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 located in the recess 27 between two circular cells 13 adjacent to the spacer support rod 17 and further adjacent to each other;
In this state, the projection 6 is moved to the opposite side of the circular elastic support member 18, and 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 support of the circular elastic support member 18 by the protrusion 6, that is, the support of the fuel spacer 23, can be easily achieved by rotating the spacer support rod 17.
can be easily supported by the spacer support rods 17. Further, since the spacer support rod 17 is inserted into the cavity surrounded by a 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, Japanese Patent Application Laid-Open No. 52-139892, Japanese Patent Application Laid-Open No. 55-72388,
JP-A-55-83881, JP-A-55-94184, JP-A-56-106183 and JP-A-56-
It is possible to use the water rod shown in Japanese Patent No. 120976 which has the function of supporting a fuel spacer.

FIG. 9 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. 8 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 positioned in the space 27 between the 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 square elastic support member 25. Then, the spacer support rod 17 is rotated so that the projection 6 comes to the position of the rectangular elastic support member 25.

This embodiment can achieve the same effect 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; FIG. 3 is a plan view of a fuel spacer used in a fuel assembly that is a preferred embodiment of the present invention;
Figure 4 is a cross-sectional view of Figure 3, Figures 5 and 6.
The figure is a side view of the circular cells 13a and 13b shown in FIG. 4, FIG. 7 is a longitudinal sectional view of another embodiment of the assembled state of the pair of circular cells shown in FIG. 4, and FIGS.
The figure is a cross-sectional view of another embodiment of the fuel assembly of the present invention. 1...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, 18... Circular elastic support member, 21...
Hole, 25... Rectangular elastic support member.

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, the fuel spacer includes a plurality of cylindrical members arranged in a grid pattern, and the cylindrical member includes: A part of the cylindrical member is configured to protrude inward, and has a plurality of arcuate protrusions that support the fuel rods inserted therein, and an elastic member that supports the fuel rods within the cylindrical member. , attached to the cylindrical member and protruding into each adjacent cylindrical member;
The protrusion and the elastic member are provided at different heights in the axial direction of the cylindrical member, and the protrusion and the cylindrical member form a passage through which a coolant passes in the axial direction of the cylindrical member. . A fuel assembly, wherein holes are formed between diagonally adjacent cylindrical members of the lattice arrangement of the cylindrical members.