JPH09264982A - Pwr fuel assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform the fixing of an uppermost-part supporting grating simply without performing a swaging process. SOLUTION: A sleeve 8, wherein a thimble tube 2 is inserted. is made to extrude from a thimble cell 6 of an uppermost-part supporting grating 3a to the vicinity of an upper nozzle plate 7. A protruding part 9, which is protruding to the outer direction or a radius is formed, at the outer surface part of the tip of the sleeve 8. A recessed part 10, which is externally coupled with the protruding part 9, is formed at the inner surface part of the lower part. Furthermore, a tubular collar 12, where the lower part is formed so that the part can be expanded, is fixed and disposed at the upper part of the thimble tube 2. The recessed part 10 of the collar 12 and the protruding part 9 of the sleeve 8 are coupled. The collar 12 is inserted to a thimble-tube inserting hole 13 of the upper nozzle plate 7. The upper nozzle plate 7 is tightened by a flange part 14 formed at the lower part of the collar and a nut 16, which is screwed into the upper part of the collar.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PWR fuel assembly, and more particularly to a fixing structure for the uppermost support grid of the fuel assembly.

[0002]

2. Description of the Related Art A PWR fuel assembly is shown in FIG.
The thimble tubes 2 are mixed into a large number of fuel rods 1 and are bundled by a plurality of support grids 3. The upper part of the thimble tubes 2 is fixed to the upper nozzle 4, and the lower part of the thimble tube 2 is fixed to the lower nozzle 5. It has a fixed structure.

The thimble tube is first attached from the lower nozzle, and the lower nozzle and the thimble tube are attached by tightening a thimble screw to a female screw at the lower portion of the thimble tube with the lower nozzle being sandwiched.

On the other hand, the upper nozzle and the thimble tube are fixed by, for example, as shown in FIG. 4, by fastening a ring nut 16 to a male screw portion 20 on the upper portion of the thimble tube 2 with a locking cup 19 interposed therebetween. To be done.

As shown in FIG. 4, an uppermost support grid 3a is arranged below the upper nozzle plate 7 at a predetermined interval. The uppermost support grid 3a is provided at the time of combustion of fuel rods. A unique fixing structure is used to prevent vertical movement due to extension.

As the above-mentioned fixing structure, conventionally, as shown in the same figure, as shown in FIG.
A method is known in which a sleeve 8'in which the thimble tube 2 is inserted is extended, and this sleeve 8'is swaged (expanded) together with the inner thimble tube 2 to integrate the sleeve 8'with the thimble tube 2. .

[0007]

However, in the above-mentioned conventional fixing structure of the uppermost support grid, the swaging process requires labor and the swage portion is formed, so that the thimble tube is short at this portion. Therefore, it is necessary to adjust the length of the thimble tube, which varies depending on the swaging process, at the lower nozzle mounting portion.

The present invention addresses the above-mentioned situation and by finding a new structure for the fixing structure of the uppermost support grid,
The purpose is to solve the above problem.

[0009]

That is, the feature of the present invention which meets the above-mentioned object is to extend a sleeve for inserting the thimble tube upward from the thimble cell of the uppermost support grid,
A PWR fuel assembly in which the uppermost support grid is fixed by engaging this sleeve with other constituent members, wherein the sleeve extends to the vicinity of the upper nozzle plate and is radially outward at the tip outer peripheral portion. A cylindrical collar is formed on the thimble tube at the upper part of the thimble tube. The concave portion of the collar is fitted into the convex portion of the sleeve, the collar is fitted into the thimble tube insertion hole of the upper nozzle plate, and the upper nozzle plate is formed by the collar portion formed on the lower portion of the collar and the nut screwed on the upper portion of the collar. It is just tightened.

In this case, it is also possible to form a plurality of split grooves in the lower portion of the collar in the substantially axial direction and to expand the lower portion of the collar by the split grooves and the elasticity of the lower portion of the collar.

[0011]

In the fuel assembly of the present invention, the recess of the collar is externally fitted to the projection of the sleeve, and the collar is fitted into the insertion hole of the upper nozzle plate to integrate the sleeve and the collar. And the top support grid is simply locked in place by this sleeve and collar combination without the need for swaging.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Referring to the accompanying drawings,
An embodiment of the present invention will be described.

FIG. 1 is a partially enlarged sectional view showing a PWR fuel assembly according to an embodiment of the present invention from an upper nozzle plate to an uppermost supporting grid, and FIG. 2 is a sectional view of FIG. 1 in which a thimble tube and an uppermost supporting grid are omitted. FIG. 3 is an exploded perspective view, and FIG. 3 is a perspective view showing an upper portion of the fuel assembly.

In the fuel assembly of the above embodiment, as shown in FIG. 3 or 5, a large number of fuel rods 1 and thimble tubes 2 are provided.
Are mixed with each other to focus them on a plurality of support grids 3, and the upper portion of the thimble tube 2 is fixed to the upper nozzle 4,
Moreover, it has an overall basic structure in which the lower portion of the thimble tube 2 is fixed to the lower nozzle 5.

In the fuel assembly of the above embodiment,
In order to fix the uppermost support grid 3a in the vertical direction, a sleeve 8 for inserting the thimble tube 2 is extended from the thimble cell 6 of the uppermost support grid 3a to the lower portion of the upper nozzle plate 7 as shown in FIG. A projecting portion 9 that projects radially outward is provided around the tip outer peripheral portion of the sleeve.

On the other hand, the concave portion 1 fitted on the convex portion 9 is externally fitted.
A thimble tube having a cylindrical collar 12 which has 0 in the entire inner circumference of the lower portion and which is capable of elastically expanding the lower portion by forming a plurality of split grooves 11 in the axial direction as shown in FIG. It is fixed to the upper part of 2 by welding.

Then, with the concave portion 10 of the collar 12 and the convex portion 9 of the sleeve 8 fitted as shown in FIG. 1, the collar 12 is inserted from below into the thimble tube insertion hole 13 of the upper nozzle plate 7. The collar 12 is fixed by fastening the upper nozzle plate 7 by the collar portion 14 formed on the lower portion of the collar and the ring nut 16 screwed onto the male screw portion 15 on the upper portion of the collar.

In this case, when the concave portion 10 of the collar 12 and the convex portion 9 of the sleeve 8 are fitted together, the inclined surface portions 17 and 18 formed on the inner peripheral portion of the lower end of the collar 12 and the outer peripheral portion of the upper end of the sleeve 8, respectively. Since the parts slide and guide each other, the lower part of the collar expands and returns only by pushing the collar 12 or the sleeve 8 to the other side, and the above fitting is automatically performed.

In this example, a locking cup 19 is interposed below the ring nut 16, and the upper portion of the locking cup 19 is provided with a notch 16a of the ring nut 16.
The ring nut 16 is prevented from rotating by swaging it.

Also in this embodiment of the invention,
The fixed structure of the uppermost support grid 3a as described above is adopted at all positions of the thimble tube 2.

Therefore, in the fuel assembly according to the embodiment of the present invention, the concave portion 10 of the collar 12 is fitted onto the convex portion 9 of the sleeve 8, and the collar 12 is fitted into the insertion hole 13 of the upper nozzle plate 7. By doing so, the lower part of the collar 12 cannot be expanded and the sleeve 8 and the collar 12 are integrated, and the uppermost support grid can be swaged by the connection of the sleeve 8 and the collar 12 without swaging. It is easily fixed in place on the fuel assembly.

[0022]

As described above, in the PWR fuel assembly of the present invention, the sleeve for inserting the thimble tube is extended from the thimble cell of the uppermost support grid to the vicinity of the upper nozzle plate, and the outer periphery of the tip of the sleeve is extended. A cylindrical collar is formed on the thimble tube at the upper part of the thimble tube. It is fixed, the recess of this collar and the protrusion of the sleeve are fitted together, the collar is inserted into the thimble tube insertion hole of the upper nozzle plate, and the collar part formed on the lower part of the collar and the nut screwed on the upper part of the collar. The upper nozzle plate is tightened by means of and the concave portion of the collar is fitted onto the convex portion of the sleeve, and the collar is fitted into the insertion hole of the upper nozzle plate. Since the collar can be integrated, it is possible to easily fix the uppermost support grid without the need for conventional swaging, which eliminates the complicated work associated with swaging and can be used for fuel assembly work. This is a remarkable effect that simplification is achieved, and the steps are shortened and the exposure during assembly work is reduced. Furthermore, by eliminating the swaging process, it is possible to eliminate the variation in the length of the thimble tube caused by this process.

[Brief description of drawings]

FIG. 1 is a partial enlarged cross-sectional view showing an upper nozzle plate to an uppermost support grid of a PWR fuel assembly according to an embodiment of the present invention.

2 is an exploded perspective view of FIG. 1 with the thimble tube and top support grid omitted.

FIG. 3 is a perspective view showing an upper portion of the fuel assembly.

FIG. 4 is an explanatory view showing a conventional fixing structure for an uppermost support grid.

FIG. 5 is an overall view of a PWR fuel assembly.

[Explanation of symbols]

 1 Fuel Rod 2 Thimble Tube 3 Support Grid 3a Top Support Grid 4 Upper Nozzle 5 Lower Nozzle 6 Thimble Cell 7 Upper Nozzle Plate 8 Sleeve 9 Convex 10 Recess 11 Groove 12 Collar 13 Thimble Pipe Insert Hole 14 Collar 15 Male Thread 16 Ring nut 16a Notch 17 Slope 18 〃 19 Rocking cup

Claims (2)

[Claims] 1. A PWR fuel in which a sleeve for inserting a thimble tube is extended upward from the thimble cell of the uppermost support grid, and the sleeve is engaged with other constituent members to fix the uppermost support grid. In the assembly, the sleeve is extended to the vicinity of the upper nozzle plate to form a convex portion that projects radially outward in the tip outer peripheral portion, and has a concave portion that is externally fitted to the convex portion in the lower inner peripheral portion, Further, a tubular collar whose lower part is expandable is fixedly mounted on the upper part of the thimble tube, and the concave part of this collar and the convex part of the sleeve are fitted to each other, and the collar is inserted into the thimble tube insertion hole of the upper nozzle plate. The PWR fuel assembly is characterized in that the upper nozzle plate is fastened by a flange portion formed on the lower portion of the collar and a nut screwed on the upper portion of the collar. 2. The PWR fuel assembly according to claim 1, wherein the lower portion of the collar can be expanded by a plurality of split grooves formed in the lower portion of the collar in the substantially axial direction and the elasticity of the lower portion of the collar.