JPH0886895A - Fuel assembly for nuclear reactor - Google Patents

Abstract

(57) [Summary] [Objective] When loaded in the reactor core, foreign matter is prevented from invading between adjacent fuel assemblies and coming into contact with the nuclear fuel rods and damaging them. [Structure] A fuel assembly for a nuclear reactor comprises an upper nozzle, a lower nozzle, a plurality of control rod guide tubes, a plurality of support grids, and a plurality of nuclear fuel rods. The lower nozzle has a coolant flow passage hole 2
1 is distributed and formed on the adapter plate 23 and legs, and a shelf 25 is formed on the lower surface of the edge portion without legs. The tray 25 forms a tray-like space below, and cooperates with that of the adapter plate of the adjacent nuclear fuel assembly to define the trapping space S.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel assembly for a nuclear reactor, and more particularly to a structure of a fuel assembly for a pressurized water reactor.

[0002]

2. Description of the Related Art At present, a fuel assembly generally used in a pressurized water nuclear reactor has a structure without an outer cylinder, that is, a can, and is mainly composed of an upper nozzle, a lower nozzle, and both nozzles. It is composed of a plurality of parallel control rod guide tubes, a support grid attached to the control rod guide tubes, and a plurality of nuclear fuel rods inserted and supported in a plurality of openings of the support grid. Such fuel assemblies are regularly arranged in the reactor vessel and used, but the plane projection shape thereof is almost square. FIG. 5 shows a perspective view of the lower nozzle 1. The lower nozzle 1 is composed of a flat adapter plate 3 and four legs 5 protruding from the four corners of the lower surface thereof, and the legs 5 are placed in contact with the lower core plate. The adapter plate 3 has a large number of coolant passage holes 7 through which the coolant flowing upward in the reactor vessel is passed. The adapter plate 3 also has symmetrically arranged control rod guide tube mounting holes 9 for receiving and connecting the ends of the control rod guide tube which also function as structural members. The edge portion of the adapter plate 3 has a shape as shown in FIG. 6, and is chamfered 3a and 3B on the top and bottom. When loaded in the core, the coolant flows as shown by the arrow F in FIG. 6, and forms a gap C between the lower nozzle of the adjacent fuel assembly and the adapter plate (shown by the chain double-dashed line).

[0003]

When the fuel assembly having the above structure is loaded in the reactor vessel, the gap C as shown in FIG. 6 becomes inevitable. Although the fuel assembly and the reactor vessel are manufactured with high precision, that is, with strict manufacturing tolerances, there are unavoidable errors and the size of the gap C is dispersed. Further, the chamfer 3a on the lower surface and the chamfer on the lower surface of the adjacent adapter plate cooperate to form a funnel-shaped cross-section flow path. Therefore, if the gap C is large, foreign substances accompanying the coolant flow may penetrate between the adjacent fuel assemblies through the gap C and come into contact with the fuel rods to cause damage. Therefore, an object of the present invention is to provide a fuel assembly for a nuclear reactor having a structure in which foreign matter does not flow between the lower nozzles of adjacent fuel assemblies.

[0004]

[Means for Solving the Problems] Under such a purpose,
According to the present invention, an upper nozzle and a lower nozzle facing each other with a large number of coolant passage holes each being cut away,
A plurality of control rod guide tubes extending in parallel to each other between the two nozzles, a support grid which receives the control rod guide tubes in an opening and is attached to intersect with the control rod guide tube, and the control grid inserted through the openings of the support grid. In a fuel assembly for a nuclear reactor composed of a plurality of nuclear fuel rods extending in parallel to a rod guide tube, an adapter for a lower nozzle composed of a rectangular adapter plate and legs protruding from four corners of the lower surface of the adapter plate. A shelf-like void is formed on the lower surface of the board edge. In this case, the shape of the shelf-like void may be a trapezoidal cross section, a trapezoid with rounded corners, or a quarter circle.

[0005]

When the fuel assembly for a nuclear reactor having the above-mentioned structure is loaded, the lower nozzles of two adjacent fuel assemblies have a substantially trapezoidal shape or a similar shape at the inlet side of the gap between them. Define a shape capture space. This capture space has an impact ceiling surface with which the coolant flow collides, and the foreign matter that accompanied the coolant stream hits the impact ceiling surface and is captured. Further, the cross-sectional area of the flow path of the coolant flow is sharply reduced between the trapping space and the gap, the amount of the coolant flowing through the gap is reduced, and the force for sucking the foreign matter is greatly reduced.

[0006]

Embodiments of the present invention will be described below with reference to the accompanying drawings. In FIG. 1, the fuel assembly 10 includes an upper nozzle 11, a lower nozzle 13, a control rod guide tube 15, nine support grids 17, and a plurality of nuclear fuel rods 19. Of course, the number of the support grids 17 is appropriately increased or decreased according to the size of the fuel assembly 10, and the control rod guide tubes 15 and the nuclear fuel rods 19 between the adjacent support grids 17 are partially cut and shortened. Is illustrated. As you can see from the figure,
Both ends of the control rod guide tube 15 extend above and below the nuclear fuel rod 19, and are connected and fixed to the upper nozzle 11 and the lower nozzle 13, respectively.

The shape of the lower nozzle 13 is roughly the same as that of FIG. 5, but the shape of the peripheral portion of the adapter plate is shown in FIG. In FIG. 2, the lower nozzle 13 has an adapter plate 23 having the coolant flow passage holes 21 formed in a distributed manner as shown in FIG. 5, and a shelf 25 is formed on the lower surface of the edge portion.
A shelf-like space is defined below the shelf 25. The upper surface of the peripheral portion is chamfered at 45 degrees similar to the conventional one. When the fuel assembly 10 having the lower nozzle 13 as described above is loaded into the reactor vessel, the lower nozzle 1
Adapter plate 23 of 3 and the adapter plate 2 of the adjacent fuel assembly
3 '(shown by a chain double-dashed line) creates a gap C, and a trapping space S having a trapezoidal cross section is defined on the inlet side thereof. And
A part of the downward flow of the coolant flowing through the coolant passage hole 21 of the adapter plate 23 flows into the capture space S and collides with the top surface thereof. At that time, the foreign matter which has waked up collides with the top surface of the trapping space S having a trapezoidal cross section and is captured. In the capture space S,
Stagnant occurs and some of the coolant flows through the gap C. Since the original function of the fuel assembly 10 and the action of the coolant flowing around the fuel assembly 10 are obvious to those skilled in the art, description thereof will be omitted.

In the above embodiment, the shelf 25 of the adapter plate 23 of the lower nozzle 13 has an obtuse trapezoidal upper left corner, but as shown in FIG. 3, the corner is rounded to a quarter.
It may be a circular tray 125, or two of these may be stacked to form a stepped tray 225 (FIG. 4). 3 and 4, reference numerals 123, 123 ', 223, 223'
Indicate adapter plates, respectively.

[0009]

As described above, according to the present invention,
Since a shelf is formed on the lower surface of the edge of the adapter plate of the lower nozzle of the fuel assembly, a trapezoidal trap space is formed at the inlet side of the gap between the lower nozzles of the adjacent fuel assemblies during core loading. The coolant wake foreign matter is prevented from being trapped here, flowing through the gap and entering between the fuel assemblies.

[Brief description of drawings]

FIG. 1 is an elevation view of a fuel assembly according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view showing a main part of the embodiment.

FIG. 3 is a partial cross-sectional view showing a main part of a modified embodiment of the present invention.

FIG. 4 is a partial cross-sectional view showing the main parts of another modified embodiment of the present invention.

FIG. 5 is a perspective view showing a lower nozzle of a conventional fuel assembly.

6 is a partial cross-sectional view taken along the line VI-VI of FIG.

[Explanation of symbols]

 10 Fuel Assembly 11 Upper Nozzle 13 Lower Nozzle 15 Control Rod Guide Tube 17 Support Lattice 19 Nuclear Fuel Rod 21 Coolant Channel Hole 23 Adapter Plate 25 Shelf 125 Shelf 225 Shelf C Gap F Coolant Flow S Capture Space

Claims (1)

[Claims] 1. An upper nozzle and a lower nozzle facing each other with a large number of coolant passage holes formed therein, and a plurality of control rod guide tubes extending in parallel between the both nozzles, and the control rod. A support grid that receives the guide tube in the opening and is attached to intersect with the control rod guide tube, and a plurality of nuclear fuel rods that are inserted into the opening of the support grid and extend parallel to the control rod guide tube. The lower nozzle is composed of a rectangular adapter plate and legs formed so as to project from the four corners of the lower surface of the adapter plate, and a shelf-like space is formed on the lower surface of the edge portion of the adapter plate without legs. A characteristic fuel assembly for a nuclear reactor.