JP3626429B2 - Fixed part of leaf spring of upper nozzle and processing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement of a leaf spring fixing portion in an upper nozzle used in a nuclear fuel assembly for a pressurized water reactor (PWR).
[0002]
[Prior art]
A PWR nuclear fuel assembly generally has a large number of fuel rods arranged in parallel, mixed with a plurality of control rod guide tubes, and vertically above the fuel bundle portions supported by a plurality of support grids at required intervals in the length direction. The upper and lower nozzles are attached to four sides with leaf springs that prevent the fuel assembly from being lifted by a cooling water flow by contacting the upper core plate.
[0003]
As shown in FIG. 3, the upper nozzle is constructed by erecting side plates 4 around the nozzle plate 1 in which a large number of water holes 2 and a required number of thimble pipe joining holes 3 are formed. The leaf spring 6 made by bending a thick plate material in the recess 5 is inserted into the insertion hole 7 (hereinafter referred to as the insertion square hole 7) and fixed with screws 8 and the distal end side Is attached by extending the guide portion 9 downward and inserting it into an insertion hole provided in the recess 5.
[0004]
As shown in FIG. 4, the square hole 7 into which the leaf spring base end is inserted is usually a rectangular parallelepiped shape, and a hole 11 is provided on the rectangular hole 7. A screw hole 10 is also formed below.
[0005]
[Problems to be solved by the invention]
However, since the square hole of the upper nozzle has a rectangular parallelepiped shape as described above, it cannot be processed by a rotary tool such as a drill during processing, and an electrode simulating the shape of the rectangular parallelepiped is used. It must be machined by electrical discharge machining.
However, unlike electric machining such as drilling, this electric discharge machining requires a great deal of time, and this machining requires several hours per location.
Accordingly, since there are four square holes per upper nozzle, it takes four times as much for one body.
[0006]
Moreover, since this long-time machining is a rate-determining process in the entire manufacturing process, it is indispensable to shorten the electric discharge machining time in order to shorten the construction period.
The present invention addresses the actual situation as described above, finds a square hole shape that can be carried out by machining without electric discharge machining, shortens the time required for machining, and simplifies fixing the leaf spring of the upper nozzle. The objective is to achieve a significant reduction in the manufacturing period throughout.
[0007]
[Means for Solving the Problems]
That is, the feature of the fit present invention the above object is achieved, one landline portion smell of the leaf springs in the top nozzle of the PWR for a nuclear fuel assembly, an oblong rectangular parallelepiped square hole for re-safe spring inserted into the square hole open end The opposing back surface is formed in a curved shape in a round shape, and the hole in the upper part of the square hole is formed in a groove shape with the leaf spring insertion side opened.
[0008]
The invention according to claim 2 is a method of processing the fixed portion, and first, by performing machining using a rotary tool from the state before the processing to the fixed portion, the groove processing in which the leaf spring insertion side is opened, Next, similarly, a rotary tool is used to perform a process of forming a rectangular parallelepiped square hole having a rounded back surface facing the insertion side open end .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Specific embodiments of the present invention will be described below based on examples shown in the accompanying drawings.
[0010]
FIG. 1 shows an example of a leaf spring fixing portion of an upper nozzle according to the present invention, and a leaf spring fixing portion A is formed at each corner portion of the upper nozzle side plate 4 as shown in FIG.
FIG. 1 shows one of the fixing portions A, and a mounting rectangular hole 7 for inserting and fixing a leaf spring base end from the side plate 4 side to the fixing portion A standing from the side plate 4 is provided in a horizontally long rectangular parallelepiped shape. The back is provided with a convexly curved roundness a.
A U-shaped groove 12 having an open leaf spring insertion side is continuously formed in the upper portion of the leaf spring insertion square hole 7.
In the figure, 10 is a screw hole as in FIG.
[0011]
2 (a), (b), and (c) show the processing method of the fixing portion A having the insertion square hole 7 as described above and the U-shaped groove-like portion 12 at the upper part in order, (B) Groove processing is performed to form a U-shaped groove-shaped portion 12 with the front face open as shown in the figure by machining from the state before processing shown in FIG. A rectangular hole 7 with a horizontally long rectangular parallelepiped shape with a leaf spring inserted therein is processed using a rotary tool such as a drill.
The rotary tool preferably has a T-shaped tip as in the case of the square hole.
Thus, machining of the groove-like portion 12 and the leaf spring insertion square hole 7 can be carried out continuously by machining, eliminating the need for electric discharge machining and greatly reducing the machining time.
In addition, the process of the screw hole 10 which existed in the square hole lower part is performed after the said process.
[0012]
In the present invention, the hole 11 on the conventional square hole 7 is changed to the groove portion 12 or the elongated hole. This groove portion 12 or the elongated hole is for accommodating the head of the leaf spring fixing screw. There is no difference in function and action even if the groove or slot is replaced. In other words, the leaf spring is maintained by the leaf spring fixing screw being securely fixed to the screw hole 10, so that there is no change.
[0013]
In the present invention, as described above, the back of the horizontally long rectangular parallelepiped rectangular hole 7 in the leaf spring fixing portion is formed in a convexly curved shape, but it can be inserted if it can be processed by the above-described T-shaped rotary tool or the like. It is also possible to make the shape suitable for the tip shape of the leaf spring.
[0014]
【The invention's effect】
In the present invention, as described above, the back of the insertion portion of the leaf spring in the fixed portion of the leaf spring in the upper nozzle of the PWR nuclear fuel assembly , that is, the back surface facing the insertion side open end is convex and curved. It is a rectangular hole with a round rectangular parallelepiped shape, and the hole at the top of the square hole is formed in a groove-like part with the leaf spring insertion side open, and it is easy to insert when inserting the leaf spring. Since it is composed of a groove-shaped part and a hole in the shape of a horizontally long rectangular body with a rounded back surface as described above, after performing groove processing by machining using a rotary tool, processing can also be performed with the rotary tool. In the conventional electric discharge machining, the machining time at four places per nozzle has reached several to several tens of hours, but by making the back surface of the square hole shape round like the present invention, this If Jo portion only will be able to work in a few tens of minutes, the time required for machining the whole fixing portion can be significantly reduced compared with the conventional.
[Brief description of the drawings]
FIG. 1 is a partial perspective view showing an example of a leaf spring fixing portion according to the present invention.
FIGS. 2A and 2B are diagrams showing a processing order of the leaf spring fixing portion of the present invention, where FIG. 2A is a pre-processing, FIG. 2B is a first processing groove processing, and FIG. 2C is a second processing insertion square hole. Shows the processing.
FIG. 3 is a perspective view showing a configuration of an upper nozzle.
FIG. 4 is a structural example of a fixing portion including a conventional leaf spring insertion square hole.
[Explanation of symbols]
A Leaf spring fixing part 1 Nozzle plate 2 Flow hole 3 Thimble pipe joint hole 4 Side plate 5 Recess 6 on the side plate upper part Leaf spring 7 Leaf spring insertion square hole 8 Screw 9 Guide part 10 Screw hole 11 Upper hole 12 Groove part a Roundness

Claims (2)

Landline portion smell of the leaf springs in the top nozzle of the PWR for a nuclear fuel assembly, an oblong rectangular parallelepiped square hole for re-safe spring inserted, Ru provided rounded the far surface facing the square hole open ends in a convex curved shape And a leaf spring fixing portion of the upper nozzle, wherein the hole in the upper part of the square hole is formed in a groove shape with the leaf spring insertion side opened. In the fixed part of the leaf spring in the upper nozzle of the nuclear fuel assembly for PWR, the fixed part is machined using a rotary tool from the state before processing, and then the groove with the leaf spring insertion side opened is processed. A method for processing a fixed part of a leaf spring of an upper nozzle, characterized in that, by using a rotary tool, a rectangular parallelepiped square hole is formed by rounding a back surface facing the insertion side open end into a convex curve .

Images