JP2517745B2 - Assembling method of nuclear fuel assembly - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for assembling a nuclear fuel assembly, and particularly to prevent the occurrence of scratches on the outer peripheral portion of a fuel rod when assembling the nuclear fuel assembly. About what you can do.

"Prior Art" As an example of a fuel assembly used in a nuclear reactor such as a pressurized water light water reactor, those shown in Figs. 9 and 10 are known.

In these drawings, reference numerals 1 and 2 denote an upper nozzle and a lower nozzle which are vertically spaced apart and opposed to each other. A plurality of control rod guide tubes 3 are provided between the upper nozzle 1 and the lower nozzle 2. Has been 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 spaced apart from each other.

Further, as shown in FIG. 10, dimples 7 and springs 8 for supporting the fuel rods 6 are formed in the wall portion forming the lattice space 5 of each support lattice 4 so as to face each other. The fuel rod 6 inserted into the space 5 has a spring 8
It is pressed against and supported by the dimple 7.

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

First, the fuel rod 6 is held and inserted by a gripper (not shown) in the lattice space 5 of the support lattice 4 supported by the control rod guide tube 3, and is pressed and fixed to the dimple 7 by the spring 8.

Then, when all the fuel rods 6 have been inserted, 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] In the method for assembling the fuel assembly, when the fuel rod 6 is inserted into the lattice space 5 of the support lattice 4, the outer peripheral surface of the fuel rod 6 is replaced by the spring 8 Since it is sandwiched between the dimple 9 and the dimple 9, the outer periphery of the fuel rod 6 has a drawback that a scratch along the axial direction is generated by the spring 8 and the dimple 7.

Therefore, in order to solve the above problems, a thin film-like resin film or the like which is long in the longitudinal direction of the fuel rod 6 is interposed between the outer peripheral surface of the fuel rod 6 and the spring 8 and the dimple 9. A method in which the rod 6 is inserted into the lattice space 5 and then the film is pulled out and taken out of the support lattice 4 can be considered.

However, in such a method, when the fuel rod 6 is inserted into the lattice space 5 or when the film is removed, the film may be broken and remain in the support lattice.
If the thickness of the film is increased so that the film does not break, the spring 8 may be pressed more than necessary by the film, the spring characteristics may change, and the holding force of the fuel rod 6 may decrease.

The present invention aims to solve the above problems.

"Means for Solving the Problem" In the method for assembling a nuclear fuel assembly according to the present invention, the nuclear fuel assembly is inserted into a lattice space of the support lattice, and is supported and fixed to the support lattice by a support portion formed in a wall portion defining the lattice space. A step of inserting the fuel rod into the lattice space with a cylindrical spacer, which is long in the longitudinal direction of the fuel rod and in which the fuel rod is arranged, interposed between the outer peripheral surface and the supporting portion; After the step, the spacer is taken out of the support grid, and the spacer has a structure of at least two layers composed of a metal thin film and a hard thin film harder than the metal thin film, and the spacer support portion. It is characterized in that at least the side in contact with is made of a hard thin film.

[Operation] According to the nuclear fuel assembly assembling method of the present invention, when assembling the nuclear fuel assembly, the fuel rods are formed in the lattice space of the supporting lattice, and the wall portion defining the lattice space with the outer peripheral surface thereof is formed. Since the cylindrical spacer is inserted between the supporting portion and the supporting portion and the spacer is pulled out, the outer peripheral surface of the fuel rod and the supporting portion do not directly slide, and therefore the fuel rod It is possible to prevent the occurrence of scratches on the outer peripheral surface.

The spacer has a structure of at least two layers including a metal thin film and a hard thin film harder than the metal thin film,
Since the side of the spacer in contact with the support portion is formed of at least a hard thin film, the tensile strength of the spacer can be increased by the metal thin film, and the hard thin film is less likely to be scratched by sliding with the support portion. The spacer can be pulled out without breaking, and the durability of the spacer can be improved.

[Embodiment] An embodiment of the method for assembling a nuclear fuel assembly according to the present invention will be described below with reference to FIGS. 1 to 7.

First, before describing the method of assembling the nuclear fuel assembly of the present invention, the spacer used in this method of assembly will be described.

That is, reference numeral 10 in FIG. 1 indicates a spacer.
The spacer 10 has a three-layer structure and is a cylindrical member extending in the longitudinal direction of the fuel rod 6 over the entire length thereof. The cylindrical resin thin film 12 located inside the spacer 10 and this thin film 12
A cylindrical metal thin film 13 is formed on the outer side of the metal thin film 13 so as to be coaxially adhered to the resin thin film 12, and on the outer side of the metal thin film 13, the metal thin film 13
It is composed of a cylindrical hard thin film 14 formed in close contact with the same 13 as the same. Also, as shown in FIG. 2, the tip of the spacer 10 engages with the tip of the pull-in rod used when the fuel rod 6 is inserted into the support grid.
Are formed.

The resin thin film 12 is made of polyester having self-lubricating property, and its film thickness is set to 10 to 40 μm.

The metal thin film 13 is made of SUS, and its thickness is set to 50 μm or more.

Further, the hard thin film 14 is made of SUS on the outer peripheral surface of the metal thin film 13.
It is formed by plating hard chrome with higher hardness, and its film thickness is set to 10 to 40 μm.

Next, a method of assembling the nuclear fuel assembly using the spacer 10 will be described.

First, the number of spacers 10 corresponding to the fuel rods 6 constituting the nuclear fuel assembly is prepared, and the fuel rods 6 are inserted into each spacer 10 as shown in FIG.

Next, as shown in FIG. 4, the spacers 10 into which the fuel rods 6 are inserted are arranged to the left of the lattice spaces 5 on the same axis of each support lattice 4, and then the lattice spaces 5 of the support lattice 4 are arranged. The tip of the pull-in rod 20 that has penetrated the inside from the right side and is inserted is engaged with the engaging portion 15 of the spacer 10 to grip the spacer 10.

Next, as shown in FIG. 5, by moving the pull-in rod 20 to the right, the spacer 10 is pulled into the lattice space 5 together with the fuel rod 6.

In this state, the dimple 7 and the spring 8 are pressed against the outer peripheral surface of the fuel rod 6 via the spacer 10 as shown in FIG. 6, whereby the fuel rod 6 is supported and fixed to the support grid 4. ing.

When all the fuel rods 6 are inserted together with the spacers 10, as shown in FIG. 7, the right end portion of the fuel rods 6 is held immovably by the fixing finger 21, and the pull-in rod 20 is moved to the right. The spacer 10 is pulled out to the outside of the support grid 4 by moving the spacer 10 toward the outside.

At this time, the outer peripheral surface of the fuel rod 6 pressed by the dimple 7 and the spring 8 relatively slides on the inner peripheral surface of the spacer 10. The inner peripheral surface has the resin thin film 12, that is, self-lubricating property. Since it is made of polyester, the spacer 10 can be smoothly pulled out.

Further, since the metal thin film 13 is formed between the outer peripheral side and the inner peripheral side of the spacer 10, the tensile strength of the spacer 10 itself is increased, so that the spacer 10 can be pulled out without breaking.

Further, since the outer peripheral surface of the spacer 10 is formed by the hard thin film 14, that is, hard chrome plating, it is difficult for the dimple 7 and the spring 8 to scratch the outer peripheral surface.
Therefore, the durability of the spacer 10 is improved.

After all the spacers 10 have been pulled out, the upper nozzle 1 and the lower nozzle 2 are fixed to both ends of the control rod guide tube 3 to complete the assembly of the nuclear fuel assembly.

According to the method for assembling the nuclear fuel assembly, the fuel rod 6 is inserted into the lattice space 5 of the support lattice 4 with the spacer 10 interposed between the outer peripheral surface of the fuel rod 6 and the dimple 7 and the spring 8, and then the spacer 10 is pulled out. So fuel rod 6
The outer peripheral surface of the fuel cell 6 and the dimples 7 and the spring 8 do not directly slide with each other, so that the occurrence of scratches on the outer peripheral surface of the fuel rod 6 can be prevented.

Further, the spacer 10 is a tubular resin thin film 12 made of polyester having self-lubricating property, a metal thin film 13 made of SUS formed outside the resin thin film 12 to enhance the tensile strength of the spacer 10, and this metal. Since the three-layer structure is formed on the outer peripheral surface of the thin film 13 and the hard thin film 14 made of hard chrome plating which is less likely to have sliding scratches due to the dimple 7 and the spring 8, the spacer 10 can be pulled out smoothly and without breaking. Can be, and spacer
The durability of 10 can be improved.

FIG. 8 shows a modification of the spacer used in the method for assembling a nuclear fuel assembly according to the present invention. The spacer 25 shown in this figure has a two-layer structure composed of the metal thin film 13 and the hard thin film 14. It is a thing.

Although this spacer 25 is slightly inferior to the spacer 10 in drawing out from the support grid 4, it has an advantage that it can be manufactured at low cost because of its simple structure.

Although the spacer 10 is formed in a cylindrical shape in the above embodiment, the spacer 10 may be formed in a polygonal cylindrical shape without being limited to this.

Further, although the hard thin film 14 is formed by hard chrome plating, it may be formed by amorphous, ceramics or the like.

Further, although the metal thin film 13 is formed of SUS, it may be formed of a metal such as titanium, nickel, or chromium.

Further, although the resin thin film 12 is formed of polyester having self-lubricating property, it may be formed of a resin containing no halogen such as nitrocellose, acrylic acid or vinyl acetate.

Further, instead of the resin thin film 12, a thin film made of zirconium or the like having a hardness lower than that of SUS may be formed.

[Advantages of the Invention] As described above, according to the nuclear fuel assembly assembling method of the present invention, the fuel rods are formed in the lattice space of the support lattice, and the outer peripheral surface of the fuel rod is formed in the wall portion defining the lattice space. Since the cylindrical spacer is inserted between the supporting portion and the supporting portion and the spacer is pulled out, the outer peripheral surface of the fuel rod and the supporting portion do not directly slide, and therefore the fuel rod It is possible to prevent the occurrence of scratches on the outer peripheral surface.

The spacer has a structure of at least two layers including a metal thin film and a hard thin film harder than the metal thin film,
Since at least the side of the spacer in contact with the support portion is formed of the hard thin film, the tensile strength of the spacer can be increased by the metal thin film, and the hard thin film is less likely to be damaged by sliding with the support portion. Therefore, the spacer can be pulled out without breaking, and the durability of the spacer can be improved.

[Brief description of drawings]

1 to 7 are for explaining one embodiment of a method for assembling a nuclear fuel assembly according to the present invention. FIG. 1 is a cross-sectional view of a spacer, FIG. 2 is a vertical cross-sectional view of a spacer, Third
The figure is a schematic view showing a state where the fuel rod is inserted into the spacer, Fig. 4 is a schematic view showing the state where the spacer is held by the pull-in rod, and Fig. 5 is a state where the fuel rod is pulled into the support grid together with the spacer. FIG. 6 is a schematic view showing a state where the spacer is pulled out, FIG. 6 is a cross-sectional view of the X circle portion in FIG. 5, FIG. 7 is a schematic view showing a state where the spacer is pulled out from the support grid, and FIG. FIG. 9 is a cross-sectional view, FIG. 9 is a front view of the nuclear fuel assembly, and FIG. 10 is a plan view of an essential part of the support grid shown in FIG. 4 ... Support lattice, 5 ... Lattice space, 6 ... Fuel rod, 7 ...
… Dimples (supporting parts), 8 …… Springs (supporting parts), 10 …… Spacers, 13 …… Metal thin films, 14 …… Hard thin films.

Claims (1)

(57) [Claims] 1. A method of assembling a nuclear fuel assembly, wherein a fuel rod is inserted into a lattice space of a support lattice, and the fuel rod is supported and fixed to the support lattice by a support portion formed on a wall defining the lattice space. In the above, the fuel rod is provided with a cylindrical spacer, which is long in the longitudinal direction of the fuel rod and in which the fuel rod is arranged, interposed between the outer peripheral surface and the support portion, and the lattice space is formed. And a step of taking out the spacer to the outside of the support grid after the step, wherein the spacer has at least two layers of a metal thin film and a hard thin film harder than the metal thin film. And a method of assembling a nuclear fuel assembly, characterized in that at least the side of the spacer in contact with the supporting portion is made of the hard thin film.