JPH07107558B2 - Fuel assembly assembly method and fuel assembly support grid - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for assembling a fuel assembly and a support grid for the fuel assembly, in which a fuel rod can be easily inserted into a grid space when assembling the fuel assembly.

[Conventional technology]

As an example of a fuel assembly loaded in a pressurized water type light water reactor, the one shown in FIG. 8 is known.

In this figure, reference numerals 1 and 2 denote an upper nozzle and a lower nozzle which are spaced apart from each other in the vertical direction and face each other, and a plurality of control rod guide tubes 3 are provided between the upper nozzle and the lower nozzle 2. It has been passed and fixed. A plurality of support grids 4 are attached to the control rod guide tubes 3 in the middle of the control rod guide tubes 3 so as to be vertically separated from each other.

As shown in FIG. 9, the support grid 4 is formed by assembling a plurality of thin strip-shaped straps 5 into a grid shape by fitting slits formed at equal intervals in the longitudinal direction of the straps 5 so as to be orthogonal to each other. A large number of lattice spaces 6 are formed, and dimples 8 and springs 9 for supporting the fuel rods 7 are formed on the wall surface forming these lattice spaces 6 so as to face each other. Then, the fuel rod 7 inserted into the lattice space 6 is dimpled 8 by the spring 9.
It is pressed and supported by.

Next, a method of assembling the fuel assembly having the above configuration will be described.

First, the support grids 4 are arranged with a predetermined gap between them,
The control rod guide tube 3 is inserted and fixed in a part of the lattice spaces 6 corresponding to each other of these support lattices 4. After that, the fuel rod 7 is inserted into the lattice space 6 of the support lattice 4 supported by the control rod guide tube 3 while sliding on the spring 9 and the dimple 8. In this way, the fuel rods 7 are arranged and fixed in the lattice spaces 6 via the springs 9 and the dimples 8. Then, after inserting all the fuel rods 7, the upper nozzle 1 and the lower nozzle 2 are fixed to both ends of the control rod guide tube 3, respectively.

[Problems to be Solved by the Invention]

By the way, in the above-described conventional method for assembling a fuel assembly, when the fuel rod 7 is inserted into the lattice space 6 of the support lattice 4, the outer peripheral surface of the fuel rod 7 is dimples 8 and springs 9.
There is a problem that the insertion work is difficult because it is sandwiched between and and must be inserted while resisting the elastic force of the spring 9. Further, usually, there is a contradictory surface between the easy insertion work and the reliable holding of the fuel rod after the insertion work.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to smoothly and easily insert a fuel rod into a lattice space, and to ensure that the fuel rod is securely inserted. Another object of the present invention is to provide a method for assembling a fuel assembly capable of supporting a fuel rod and a support grid for the fuel assembly.

[Means for Solving the Problems]

In order to achieve the above object, a method for assembling a fuel assembly according to the present invention is such that a free end of a cantilevered spring formed along a direction orthogonal to a fuel rod insertion direction is attached to a pressing means in a fuel rod insertion direction. Is inserted into the lattice space along the line to push the fuel rod to the outside of the lattice space, and after inserting the fuel rod into the lattice space, the pressing means is removed and the spring is pressed against the fuel rod.

Further, in the fuel assembly support grid of the present invention, a cantilevered spring is formed along the longitudinal direction of the strap, and free ends of a pair of springs corresponding to one grid space are formed alternately. Locking portions are formed at the free ends of these springs for engaging the pressing means for pressing the springs outward of the lattice space.

[Action]

In the fuel assembly assembly method and fuel assembly support grid of the present invention, the free end of the cantilevered spring is inserted into the grid space by inserting the pressing means into the grid space along the fuel rod insertion direction. By inserting the fuel rods into the lattice space while pressing outward, it becomes difficult for the springs or dimples to come into contact with the fuel rods when inserting the fuel rods.
The fuel rod can be easily inserted, and the spring is pressed against the fuel rod by removing the pressing means after the fuel rod is inserted, and the fuel rod is reliably supported by the spring and the dimple.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 7.

FIG. 1 is a perspective view showing a support grid according to a first embodiment of the present invention. This support grid 10 is one in which outer straps (not shown) are attached to the four circumferences of an inner strap 10a assembled in a grid shape, and a wall portion 10a forming a grid space 10b is arranged in the longitudinal direction of the strap. Two rows of dimples 10c are formed so as to project to one side. And Dipple 10
Corrugations 10d are formed above and below c. Further, between the pair of upper and lower dimples 10c, a cantilevered spring 10e is formed so as to protrude in a direction opposite to the protruding direction of the dimple 10c along the longitudinal direction of the strap, and one lattice space is formed. Tip portions 10f of adjacent springs 10e in 10b are arranged so as to mesh with each other in an alternating manner, and are formed to be curved. The push rod 11a of the retainer 11 is adapted to engage with the tips 10f of the springs 10e. This presser foot 11
The holding portion 11b is provided at the base end of the pressing rod 11a so as to straddle the strap. Further, the pressing rod 11a
Has a tapered tip, and the holding portion 11b
An inclined surface 11c is formed at the tip of the so as to face the pressing rod 11a.

When the fuel rod is inserted into the lattice space of the support lattice constructed as described above, the holding tool 11 is inserted into the lattice space 10b prior to inserting the fuel rod. In this case, as shown in FIGS. 2 to 5, when the pressing rod 11a is in contact with the tips 10f of the two springs 10e adjacent to each other, the holding portion 11b is held.
While the end of the strap 10a is in contact with the inclined surface 11c, the strap 10a is fitted into the holding tool 11. As a result, the pressing rod
Since 11a presses the tips 10f of both springs 10e toward the corners of the lattice space 10b, as shown in FIG. 3, the spring 10e and the dimples facing the spring 10e
A sufficient gap is secured between 10c and the fuel rod 12 to be inserted therethrough.

In this state, after the fuel rods 12 are easily inserted, if the retainer 11 is pulled out from the lattice space 10b, the pressing force that has hitherto pushed each spring 10e to the outside of the lattice space 10b is removed. The spring 10e moves to the inner side of the lattice space 10b, and the fuel rod 12 moves to the spring 10e.
It is surely supported between the dimple and the dimple 10c. Instead of using the pressing tool 11, the pressing rod (pin) may be moved by an automatic device to be inserted into and removed from the lattice space.

6 and 7 show a second embodiment of the present invention. In this embodiment, the tip portions 1 of the adjacent springs 10g in one lattice space 10b which mesh with each other alternately.
0h, 10h is formed so as to linearly extend toward the corner of the lattice space 10b, and in the corner of the lattice space 10b, before and after each of the springs 10g, the inner side of the lattice space 10b. A key support portion 10i is formed so as to protrude to the outside, and a protrusion 10j for supporting the fuel rod in contact therewith is formed at an intermediate portion of the spring 10g.

As a result, before inserting the fuel rod, the key 13 is inserted into the space surrounded by the tip portion 10h of the spring 10g and the key support portion 10i while the spring 10g is pressed to the outside of the lattice space 10b. By doing so, the fuel rod can be easily inserted into the lattice space 10b, and by pulling out the key 13, the fuel rod can be reliably supported by the spring 10g and the dimple. In this way, by inserting / removing the key 13 along the fuel rod insertion direction, it is possible to operate the spring 10g with one key 13 over several support grids.

〔The invention's effect〕

As described above, in the method for assembling the fuel assembly of the present invention, the free end of the cantilevered spring formed along the direction orthogonal to the fuel rod insertion direction is connected to the pressing means along the fuel rod insertion direction. By pushing it into the lattice space, it pushes outward from the lattice space, and after inserting the fuel rods into this lattice space,
Since the pressing means is removed and the spring is pressed against the fuel rod, the free end of the cantilevered spring is pressed to the outside of the lattice space by the pressing means inserted into the lattice space, By inserting the fuel rods into the lattice space, it becomes difficult for the springs or dimples to come into contact with the fuel rods when inserting the fuel rods, the fuel rods can be easily inserted, and scratches are formed on the outer surface of the fuel rods. It can be prevented from occurring.

Further, in the fuel assembly support grid of the present invention, a cantilevered spring is formed along the longitudinal direction of the strap, and free ends of a pair of springs corresponding to one grid space are formed alternately. At the free ends of these springs, locking portions for engaging the pressing means for pressing the springs to the outside of the lattice space are formed, so by removing the pressing means after inserting the fuel rod, By pressing the spring against the fuel rod, the fuel rod can be reliably supported by the spring and the dimple.

[Brief description of drawings]

1 to 5 show a first embodiment of the present invention. FIG. 1 is a perspective view, FIG. 2 is an explanatory view of a state before a spring is biased by a presser, and FIG. 3 is FIG. 4 is an explanatory view of a state in which a spring is biased by a presser, FIG. 4 is an explanatory view of the state shown in FIG. 2 seen from the side, and FIG. 5 is an explanatory view of the state shown in FIG. And FIG. 7 show a second embodiment of the present invention. FIG. 6 is a perspective view, FIG. 7 is a plan view when a key is inserted, and FIG. 8 is a front view of a conventional fuel assembly. FIG. 9 is a plan view of a conventional support grid portion. 10 …… Support grid, 11 …… Presser foot, 12 …… Fuel rod, 13 ……
Key, 10a …… Inner strap (wall), 10b …… Lattice space, 10c …… Dimple, 10e …… Spring, 10f ……
Tip (free end), 10g ... Spring, 10h ... tip (free end), 11a ... Pressing rod.

Front page continued (72) Inventor Akio Yamato 622-1, Funaishikawa, Tokai-mura, Naka-gun, Ibaraki Prefecture Mitsubishi Nuclear Fuel Co., Ltd. Tokai Works (72) Inventor Mitsuru Mamoru, 622, Funaishikawa, Tokai-mura, Naka-gun, Ibaraki Prefecture Mitsubishi Nuclear Fuel Co., Ltd., Tokai Works (72) Inventor, Isamu Hayashi, 622, Funaishikawa, Tokai-mura, Naka-gun, Ibaraki Prefecture Mitsubishi Nuclear Fuel Co., Ltd., Tokai Works (56) References JP 61-225695 (JP, A) ) Actual development Sho 62-155398 (JP, U)

Claims (2)

[Claims] 1. A fuel rod is inserted into a lattice space of a support lattice,
When assembling the fuel assembly in which the fuel rods are supported by the dimples and springs formed opposite to the wall defining the lattice space, a cantilever shape is formed along the direction orthogonal to the fuel rod insertion direction. The free end of the spring is pushed into the lattice space by inserting the pressing means into the lattice space along the insertion direction of the fuel rod, and is pushed outward in the lattice space.After inserting the fuel rod into the lattice space, the pressing means is removed, A method of assembling a fuel assembly, wherein the spring is pressed against the fuel rod. 2. A plurality of thin strip-shaped straps are crossed with each other to form a large number of lattice spaces, and a spring and a dimple arranged to face the spring are formed on the strap forming the lattice spaces. In the support lattice of the fuel assembly, a cantilevered spring is formed along the longitudinal direction of the strap, and free ends of a pair of springs corresponding to one lattice space are formed alternately, and these springs are formed. 2. A support grid for a fuel assembly, wherein a locking portion for engaging with a pressing means for pressing the spring to the outside of the lattice space is formed at the free end of the fuel assembly.