JPH052957B2 - - 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 constituting 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 daily minimum value of the critical power (referred to as minimum critical power ratio, MCPR) with respect to the power of the fuel assembly during nuclear reactor operation.

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

An object of the present invention is to provide a fuel assembly that can reduce pressure loss in a fuel spacer, increase thermal margin, and prevent boiling transition.

A feature of the present invention is that the fuel spacer includes a plurality of cylindrical members arranged in a lattice pattern into which fuel rods are inserted, and a space is provided between the cylindrical members adjacent to each other in a diagonal direction of the lattice arrangement of the cylindrical members. a hole is formed in the cylindrical member, the cylindrical member has a plurality of protrusions projecting inwardly to support the fuel rods in the radial direction, and an elastic support member supporting the fuel rods in the radial direction is adjacent to the cylindrical member. The elastic support member is provided through a cylindrical member and protrudes into the adjacent cylindrical member, and the length of the elastic support member in the axial direction of the cylindrical member is shorter than that of the cylindrical member, and A coolant passageway is formed inside the resilient support member through which coolant can flow through the resilient support member, the resilient support member being within the cylindrical member and axially of the fuel rod. It's about supporting one place.

According to this feature, the coolant passage through which the coolant can flow through the elastic support member in the axial direction of the cylindrical member is formed inside the elastic support member, so that the fuel spacer in the axial direction The projected area can be reduced. Further, since the length of the elastic support member in the axial direction of the cylindrical member is shorter than that of the cylindrical member, the length of the wetted area in the axial direction of the elastic support member is shortened, and frictional pressure loss can be reduced. Such a reduction in the projected area and the length of the wetted area contributes to a significant reduction in the pressure loss of the fuel spacer.

Since the holes are formed between diagonally adjacent cylindrical members in the lattice-like arrangement of the cylindrical members, the thermal margin, that is, MCPR, can be improved.

In addition, the elastic support member having the coolant passage formed inside thereof through which the coolant can flow in the axial direction of the cylindrical member can contribute to reducing the projected area of the fuel spacer as described above. Furthermore, by supporting the fuel rod at one location within the cylindrical member in the axial direction, it is possible to prevent boiling transition from occurring on the surface of the fuel rod.

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. Elastic support part 16
is composed of a circular elastic body with a cylindrical shape,
It is attached by penetrating two 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,
The circular cell 13b has a rectangular slit 16b in the axial center of the side wall. Elastic support part 16
is the adjacent circular cell 13 as shown in FIG.
Opposed U-shaped slits 16a of a and 13b
and is inserted and attached into the rectangular slit 16b. A portion of the elastic support portion 16 protrudes into the circular cell 13a, and another portion 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 length of the elastic support portion 16 in the axial direction of the circular cell is equal to the length of the circular cell 13.
It is shorter than the axial lengths of a 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. Since the length of the elastic support part 16 in the axial direction of the circular cell is shorter than the length of the circular cell in the axial direction, the length of the wetted edge of the elastic support part 16 in the axial direction is shorter than that of the conventional lantern box 9. , frictional pressure loss due to the elastic support portion 16 is significantly reduced. Due to such a reduction in projected area and shortened axial wetted edge length, the pressure loss of the fuel spacer 14 is significantly lower than that of the conventional fuel spacer 2. Furthermore, 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 in the axial direction of the fuel rod is reduced, and the pressure loss of the fuel spacer 14 can be further reduced. Since the elastic support portion 16 supports one portion of the fuel rod 1 within the circular cell 13 and in the axial direction, no coolant addition occurs on the surface of the fuel rod 1, and boiling transition, that is, burnout occurs. do not have.

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.

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 (or 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 the circular cells 13 are connected to the U-shaped slits 16a shown in FIG.
A circular cell 13a having
Two cells 13a are assembled upside down, one circular elastic body 16 is attached in each slit, and the upper and lower ends of the circular cells 13a are joined by welding (FIG. 8). In the fuel spacer of this embodiment, only one type of circular cell 13a is required for the circular cell 16, and manufacturing is easier than in 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 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. The circular elastic support member 18 has a cylindrical shape like the circular elastic body that constitutes the elastic support section 16. In the fuel assembly of this embodiment, two spacer support rods 17 are inserted into a gap formed by surrounding a plurality of circular cells 13. This gap is formed within the fuel spacer 23.

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 locked to the spacer support rod. This is because the length of the projection supporting the fuel spacer in the radial direction cannot be increased because the spacer support rod is inserted into the circular cell. In this embodiment, in order to solve this problem, a spacer support rod 17 is inserted into a gap formed by being surrounded by a plurality of circular cells 13, and a spacer support rod 17 is inserted between circular cells 13 adjacent to this spacer support rod 17. A circular elastic support member 18 is arranged and attached to the circular cell 13. Furthermore, a circular elastic support member 18 is supported by a protrusion 6 provided on one spacer support rod 17. The space into which the one spacer support rod 17 described above is inserted is 1
Two circular cells 13 are removed and formed. It can be said that this gap has a size that allows the circular cell 13 to be placed therein. A circular cell 13 adjacent to each spacer support rod 17, e.g. circular cell 13c
has a rigid support member 15a that protrudes outward. The spacer support rods 17 extend between the two rigid support members 1 in a direction perpendicular to the axis of the fuel assembly.
5a and a circular elastic support member 18. 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 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 the projection 6 is moved to the opposite side of the circular elastic support member 18, the spacer support rod 17 is rotated to make the projection 6 into a circular shape. 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 projection 6 supports the lower surface of the circular elastic support member 18.
The locking operation of the projection 6 to the circular elastic support member 18 can also be performed as follows. That is,
A recess 2 between two circular cells 13 which are adjacent to the spacer support rod 17 and which are further adjacent to each other.
7, and in that state, move the protrusion 6 to the opposite side of the circular elastic support member 18, and rotate the spacer support rod 17 so that the protrusion 6 comes to the position of the circular elastic support member 18. be.

In the fuel assembly of this embodiment, the pressure loss of the fuel spacer is reduced and the MCP 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.

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. 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 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 18.

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 present invention, the pressure of the fuel spacer is reduced by reducing the projected area of the fuel spacer in the axial direction and reducing the friction pressure loss based on the shortening of the wetted edge length in the axial direction of the cylindrical member of the elastic member supporting the fuel rod. Loss can be reduced. Furthermore, 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. The elastic support member formed with the coolant passage formed inside the cylindrical member through which the coolant can flow in the axial direction can contribute to reducing the projected area of the fuel spacer as described above, and furthermore, the elastic support member can contribute to reducing the projected area of the fuel spacer, and By supporting the fuel rod at one location within the member and in the axial direction, it is possible to prevent boiling transitions from occurring on the surface of the fuel rod.

[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.
9 is a side view of the circular cells 13a and 13b shown in FIG. 4, FIGS.
1 and 10 are cross-sectional views of other embodiments of the fuel assembly of the present invention. DESCRIPTION OF SYMBOLS 1... Fuel rod, 4... Upper tie plate, 5... Lower tie plate, 13... Circular cell, 14, 23, 2
4... 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)

[Scope of 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 is arranged in a lattice shape, and each of the fuel rods is arranged inside the fuel spacer. a plurality of cylindrical members to be inserted; a hole is formed between the cylindrical members adjacent in a diagonal direction of the lattice-like arrangement of the cylindrical members; An elastic support member having a plurality of protrusions supporting fuel rods and supporting the fuel rods in the radial direction is provided through the adjacent cylindrical member and protrudes into the adjacent cylindrical member, and the elastic support member radially supports the fuel rod. The length of the elastic support member in the axial direction of the cylindrical member is shorter than that of the cylindrical member, and a coolant passage through which the coolant can flow through the elastic support member is provided in the axial direction of the cylindrical member. , formed inside the elastic support member, wherein the elastic support member supports one portion of the fuel rod in the axial direction within the cylindrical member.