JPH11183675A - Pressure spring for fuel assembly and its mounting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily mount the pressure spring of a fuel assembly for a pressurized water reactor. SOLUTION: A pressure spring 30 for a fuel assembly is provided with an upper leaf spring 40 that has a base end 43 being joined and fixed onto the upper surface of the upper nozzle of a fuel assembly for a reactor and a force operation end part being provided with a vertical guide part 49 and being displaced, and is inserted into and passes through a guide long hole 61 where the guide part 49 is formed on the upper surface part of the upper nozzle. The pressure spring 30 has also a narrow width part 49a where the guide part 49 of the upper leaf spring 40 can be rotated around a long shaft in the guide long hole 61 and a tip part 49c where a sideward projection 49d being gear- locked onto the lower surface of the guide long hole 61. In the pressure spring 30, the length from the tip part 49c of the guide part 49 to the lower end of the narrow width part 49a is set longer than distance from a nozzle bottom plate of the upper part nozzle to the lower surface of the guide long hole 61.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel assembly used for a nuclear reactor, and more particularly, to a presser spring provided on an upper part thereof and a method of mounting the same.

[0002]

2. Description of the Related Art A fuel spring of a pressurized water reactor widely used at present for power generation uses a presser spring at an upper portion thereof. In summary, as shown in FIG. 6, the fuel assembly 10 placed between the lower core plate 1 and the upper core plate 3 in the reactor includes an upper nozzle 11, a lower nozzle 13, and a plurality of parallel nozzles. Control rod guide tube 15, a plurality of support grids 17 fixed to the control rod guide pipe 15 at intervals in the longitudinal direction, and a plurality of fuel rods inserted and supported one by one in a plurality of grid openings of the support grid 17. 19. A presser spring 20 is attached to the upper surface of the upper nozzle 11 in order to absorb an increase in the overall height due to irradiation growth of the fuel assembly 10 and further to prevent the fuel assembly 10 from floating due to a coolant flow. A typical structure of the holding spring 20 is as follows.
This is disclosed in Japanese Utility Model Publication No. 5-6557.

The structure of such a pressing spring 20 and the structure of its mounting portion will be described below. As shown in FIGS. 7 and 8, an upper nozzle 11 is provided with a mounting hole 11a for mounting a control rod guide tube 15. Further, it comprises a nozzle bottom plate 11b having a coolant flow-through hole (not shown) and a rectangular cylindrical main body 11c to which a pressing spring 20 is attached on the upper surface.
The holding spring 20 has a laminated leaf spring (leaf spring) structure, and four sets are provided along the side of the upper surface of the main body 11c. As apparent from FIG. 8, particularly, the upper leaf spring 21 and the lower leaf spring 23 are provided. These base ends are fixed to the corners of the upper surface of the rectangular cylindrical main body 11 in a jointly fastened state by bolts 25. The force-operating end of the presser spring 20 protrudes above the upper surface of the upper nozzle 11, and comes into contact with the lower surface of the upper core plate 3 when the fuel assembly 10 is loaded into the core (see FIG. 5). At the working end, the upper leaf spring 21 is bent downward to form a vertical guide portion 21a, and the guide portion 21a is
Through the guide slot 11d.

The details of the structure of the guide portion 21a of the upper leaf spring 21 are shown in FIGS. Guide part 21a
Is narrower than the main body 21b of the upper leaf spring 21, and a locking projection 21c protruding laterally is formed at the distal end thereof. The locking projection 21c is
It has a function of preventing it from detaching from the upper nozzle 11 and becoming a detached foreign matter in the nuclear reactor when it breaks near the base end fixing portion. Incidentally, the stress generated when the upper leaf spring 21 is deformed becomes maximum near the base end similarly to the case of the beam fixed at one end. Furthermore, since the surrounding environment at the time of use is in a high-temperature hot water state, the use atmosphere is under severe conditions. For this reason, it is not always the case that breakage near the base end fixed portion occurs due to an unexpected cause, and it is intended to prevent occurrence of an undesired situation due to the falling off. However, as can be seen from FIG. 9, if there is a locking projection 21c at the tip of the guide portion 21a, it becomes wider than the width of the guide elongated hole 11d, and cannot be simply inserted. For this reason, a slot 21d is formed in the guide portion 21a, and the leading end portion is divided into two legs 21e and 21f, which are joined by a split joining surface 21g. This divided mating surface 21g is shown in FIG.
It is stepped as shown in FIG.

In order to insert the guide portion 21a of the upper leaf spring 21 having such a structure into the guide elongated hole 11d, it is twisted to a state shown in FIG. 11 by using a special tool (not shown). A torsional reaction force is generated in the legs 21e and 21f, and the legs 21e and 21f try to return.
At this time, since the width of the distal end portion is smaller than the width of the guide elongated hole 11d, the portion of the locking projection 21c easily passes through the guide elongated hole 11d. Thereafter, using the special tool again, FIG.
Alternatively, the guide portion 21a is returned to the state shown in FIG. In a conventional holding spring, the number of lower leaf springs is 2 or 3
However, the basic structure of the upper leaf spring is the same as described above.

[0006]

In the above-mentioned conventional presser spring, the guide portion of the upper leaf spring is formed so as to be capable of torsional deformation. It is very good in that it only needs to be twisted and does not require other operations such as welding.However, a slot is formed in the guide portion of the upper leaf spring, or a split mating surface is Or to form
There is a problem that the manufacturing cost of the upper leaf spring alone increases. Further, there is a problem that the special tool is required even though the assembly is simple. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a pressure spring for a fuel assembly, which has a low manufacturing cost of a single unit and does not require a special special tool or the like at the time of assembly. It is a further object of the present invention to provide a method for attaching a presser spring having such a structure to an upper nozzle of a fuel assembly at low cost.

[0007]

According to the present invention, there is provided a fuel assembly for a nuclear reactor having a guide portion perpendicular to a base end fastened and fixed on an upper surface of an upper nozzle of the fuel assembly. A pressurizing spring for a fuel assembly having a force-operating end portion that displaces and a leaf spring in which the guide portion is inserted through a guide elongated hole formed in the upper surface of the upper nozzle; A narrow portion rotatable around the longitudinal axis in the hole, and a distal end formed with a lateral projection locked on the lower surface of the guide elongated hole, from the distal end of the guide portion to the lower end of the narrow portion. Is set to be longer than the distance from the nozzle bottom plate of the upper nozzle to the lower surface of the guide slot.
According to the present invention, in order to further solve the above another problem,
When attaching the presser spring configured as described above to the upper nozzle of the fuel assembly, the guide portion of the plate spring is passed through the guide elongated hole of the rectangular cylindrical body of the upper nozzle before the nozzle bottom plate is joined, and the narrow width is obtained. The leaf spring is rotated by approximately 90 degrees with the part positioned in the guide elongated hole so that the direction of the leaf spring and the direction of the guide elongated hole are aligned, and the base end of the leaf spring is fastened and fixed to the upper surface of the main body. Then, the nozzle bottom plate is welded to the lower surface of the main body.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, referring to FIG. 1, the holding spring 30 has a laminated leaf spring (leaf spring) structure including a lower leaf spring 31 and an upper leaf spring 40.
The upper leaf spring 40 has a base end 43 having a mounting bolt hole 41, a main body part 45 inclined upward, a bent part 47, and a vertical guide part 49. The guide part 49 is narrower than the main body part 45 as a whole, but has a narrow part 49a having the narrowest width at the upper part, and further has an intermediate part 49b at the lower part.
In addition, a side projection 49d is provided at the tip portion 49c. The diagonal distance of the cross section of the narrow portion 49a having a rectangular cross section is smaller than the width W of the guide long hole 61 of the upper nozzle conceptually shown, and the length L is larger than the depth D of the guide long hole 61. Is also slightly larger. Therefore, if the narrow portion 49a is located at the position of the guide elongated hole 61, even if the upper leaf spring 40 is rotated around the longitudinal axis of the guide portion 49, it does not interfere with the upper nozzle. Further, the width w of the intermediate portion 49b is slightly smaller than the width W of the guide elongated hole 61 and is substantially guided at this portion, but since the diagonal distance of the cross section is larger than the width W of the guide elongated hole 61, This part cannot rotate around the longitudinal axis in the guide slot 61. Further, the width of the distal end portion 49c is considerably larger than the width W of the guide slot 61, including the height of the projection 49d. Therefore, once the distal end portion 49c of the guide portion 49 has passed through the guide elongated hole 61, it cannot be removed.
The length from the lower end of the narrow portion 49a of the guide portion 49, that is, the upper end of the intermediate portion 49b to the distal end surface of the distal end portion 49c is:
This will be described later. In the structure of the lower leaf spring 31, a bolt hole similar to the mounting bolt hole 41 is formed at the base end 33, and a long hole through which the guide portion 49 passes is formed at the distal end portion 35 so as to extend in the width direction. , And the upper leaf spring 40.

A procedure for attaching the presser spring 30 having the above structure to the upper nozzle 60 will be described below. (A) First, as shown in FIG. 2, the pressing spring 3 is attached to the square tubular main body 63 of the upper nozzle 60 to which the nozzle bottom plate is not joined.
The guide portion 49 of the upper leaf spring 40 is inserted. At this time, the width direction of the guide portion 49 is aligned with the longitudinal direction of the guide long hole 61 so that the distal end portion 49c of the guide portion 49 passes through the guide long hole 61. Therefore, as is clear from the figure, the main body 43 of the upper leaf spring 40 and the lower leaf spring 31
Is intersected with the longitudinal axis of the guide slot 61. (B) Next, as shown in FIG.
a is overlapped with the guide slot 61, the guide portion 4
9 is rotated 90 degrees about its longitudinal axis so that the upper leaf spring 40
The longitudinal axes of the main body 43 and the lower leaf spring 31 are aligned with the longitudinal axis of the guide slot 61 in the same direction. This state is shown in FIG. (C) Next, as shown in FIG. 4, the base end 43 of the upper leaf spring 40 of the holding spring 30 and the base end 33 of the lower leaf spring 31 are tightened and fixed by the mounting bolts 65. Then,
The posture of the holding spring 30 is as shown in the figure. Such insertion, tightening and fixing are performed for all of the four pressing springs 30. Thereafter, the nozzle bottom plate 67 is joined to the lower surface of the rectangular cylindrical main body 63 by welding.

The upper nozzle 60 to which the presser spring 30 is attached in the above procedure is assembled into a fuel assembly as described in the section of the prior art, and is used by being loaded on the reactor core. If the upper leaf spring 40 and the lower leaf spring 31 of the presser spring 30 break during the use of the fuel assembly near the base end mounting portion as shown in FIG. 49 falls into the guide slot 61. However, the end face of the tip portion 49c contacts the upper surface of the nozzle bottom plate 67 and does not drop any more. At this time, the lower end portion of the narrow portion 49a is
1, which is above the lower opening, ie, the lower opening surface,
9 does not rotate. Conversely, the above-described length of the guide portion 49 is determined so as to secure this function.

[0011]

As described above, according to the present invention,
It is only necessary to make a notch in the guide part of the leaf spring that constitutes the presser spring to form a narrow part, so that the manufacturing cost can be reduced, and by setting the length of the guide part properly, breakage can occur. Even if there is, it can be prevented from falling off. Furthermore, according to the present invention, by appropriately selecting the procedure of assembling the upper nozzle and attaching the presser spring, the upper nozzle can be attached undetachably by rotating the presser spring without any special tool. , The assembly cost can be reduced.

[Brief description of the drawings]

FIG. 1 is an overall perspective view showing an overall structure of a holding spring according to an embodiment of the present invention.

FIG. 2 is an explanatory view showing one stage of a mounting procedure of the pressing spring.

FIG. 3 is an explanatory view showing one stage of a mounting procedure of the pressing spring.

FIG. 4 is an explanatory view showing one stage of a mounting procedure of the pressing spring.

FIG. 5 is an explanatory diagram illustrating an operation of the embodiment.

FIG. 6 is an elevation view showing an example of a fuel assembly for a reactor including a presser spring to which the present invention is applied, which is partially cut away and shortened.

FIG. 7 is a partially cutaway perspective view of an upper nozzle to which a conventional holding spring is attached.

FIG. 8 is a vertical sectional view of the conventional upper nozzle.

9 is a partially enlarged sectional view of FIG.

FIG. 10 is a partially enlarged perspective view corresponding to FIG. 9;

FIG. 11 is a partial perspective view showing one stage of a procedure for attaching a conventional holding spring.

[Explanation of symbols]

 Reference Signs List 30 holding spring 31 lower leaf spring 33 proximal end 35 distal end 40 upper leaf spring 41 mounting bolt hole 43 proximal end 45 main body 47 bent portion 49 guide portion 49a narrow portion 49b middle portion 49c tip portion 49d side protrusion 60 upper nozzle 61 Guide long hole 63 Main body 65 Mounting bolt 67 Nozzle bottom plate

Claims (2)

[Claims] 1. A reactor having a base end fastened and fixed on an upper surface of an upper nozzle of a fuel assembly for a nuclear reactor and a displacing force acting end provided with a vertical guide portion, wherein the guide portion is provided on the upper nozzle. A fuel assembly holding spring having a leaf spring inserted through a guide elongated hole formed in an upper surface portion, wherein the guide portion includes a narrow portion rotatable around a longitudinal axis in the guide elongated hole and the guide length. A tip formed with a lateral projection locked to the lower surface of the hole, wherein a length from the tip of the guide portion to the lower end of the narrow portion is set from the nozzle bottom plate of the upper nozzle to the guide. A presser spring for a fuel assembly, wherein the presser spring is set to be larger than a distance to a lower surface of the long hole. 2. A reactor having a base end fastened and fixed on an upper surface of an upper nozzle of a fuel assembly for a reactor and a displacing force acting end provided with a vertical guide portion, wherein the guide portion is provided on the upper nozzle. A fuel assembly presser spring having a leaf spring inserted into a guide elongated hole formed in an upper surface portion is provided with a rectangular cylindrical main body having an upper surface portion provided with the guide elongated hole and a number of coolant flow-through holes. When attaching to the upper nozzle composed of a nozzle bottom plate, a guide portion of the leaf spring is passed through the guide elongated hole of the main body before the nozzle bottom plate is joined, and the narrow portion is positioned in the guide elongated hole. Rotating the leaf spring substantially 90 degrees while keeping the direction of the leaf spring and the direction of the guide slot, fastening and fixing the base end of the leaf spring to the upper surface of the main body, the lower surface of the main body Characterized in that the nozzle bottom plate is welded to To install the fuel assembly holding spring.