JPH056560Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a support grid storage getter box used when brazing the support grid of a nuclear reactor fuel assembly.

[Prior Art] A fuel assembly loaded into a nuclear reactor is formed by arranging a large number of long fuel rods, in which a large number of short cylindrical pellets are sealed, parallel to each other at regular intervals. ing. In this case, a support grid is used as a means for holding the fuel rods in this positional relationship.

As shown in Fig. 5, this support grid has a structure in which thin plate-shaped inner straps 1 are assembled in a grid shape, and outer straps 2 are attached to the outer periphery of the support grid. name) is used.

This support grid is assembled as follows.

Each inner strap 1 is provided with a large number of slits at regular intervals in a direction perpendicular to its longitudinal direction, and side tabs are formed to protrude from both longitudinal ends. Then, the slits of the straps 1 constituting the vertical members and the slits of the straps 1 constituting the horizontal members are butted against each other, and while holding these straps 1 in a positional relationship perpendicular to each other, the slits are fitted into each other and assembled vertically and horizontally into a lattice. form into a shape.

On the other hand, on the outer strap 2, there are
A large number of slots are formed. Then insert slots around the four circumferences of inner strap 1.
Attach the outer strap 2 to the inner strap 1 by fitting it into the side tab of the strap. Then, each side tab of the inner strap 1 is folded to form the strap assembly.

Next, the intersection points of each strap 1 and 2 are brazed. This brazing method involves coating the upper part of each strap 1 and 2 with an amount of brazing material that covers the line where the straps 1 and 2 intersect, and placing the brazing material in a vacuum brazing furnace. Vacuum the inside,
Heat to the specified brazing temperature. Then, the brazing material melts and flows down the area where the straps 1 and 2 intersect, and this area is covered with the brazing material. Thereafter, by lowering the temperature in the furnace, each strap 1, 2 is joined with a brazing filler metal.

After this, each side tab protruding from the outer strap 2 is ground away, this part is finished and then aged to form the final support grid.

Between each lattice of the support lattice constructed in this way,
By inserting fuel rods and installing support grids at several locations in the longitudinal direction of the fuel rods, it is possible to construct a fuel assembly in which a large number of fuel rods are supported in parallel at regular intervals.

In the above assembly process, when brazing each intersection of the straps 1 and 2,
The flux mixed in the brazing material turns into gas,
On the other hand, the alloy material that constitutes the support grid contains Al,
The flux contains metals such as Ti and Nb that have a high affinity for oxygen. Therefore, even though the flux is processed in a vacuum brazing furnace, these metals tend to combine with the oxygen in the flux gas, forming an oxide film on the surface of each strap 1, 2.
The flow of the brazing material is poor on the surface of the support grid 2. The so-called wettability is poor, so the brazing material is difficult to flow off, and as a result, the brazing material does not adhere to the entire area where the straps 1 and 2 intersect, and so-called voids are generated where the brazing material is interrupted. When this happens, the straps 1 and 2 are not brazed firmly, which leads to a lack of strength in the support grid itself.

Therefore, conventionally, in order to eliminate the above-mentioned problems during brazing, a pretreatment such as Ni plating is performed in advance to prevent oxidation and improve wettability of the surface of the support grid.

[Problems to be solved by the invention] By the way, in order to plate the surface of the support grid with Ni, there is a problem that it takes time and effort, increases the number of work steps, and increases cost. was. In addition, there was a risk that radiation sources would be generated due to radiation exposure, increasing the amount of radiation exposure at the plant.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a getter box for storing a support grid when the support grid is brazed in a vacuum brazing furnace. Among the metals contained in the alloy that makes up the lattice,
It is characterized in that the box is made of a metal that has a higher affinity for oxygen than the metal that has the highest affinity for oxygen, and that the box has a large number of holes that communicate between the inside and the outside of the box.

[Embodiments] Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 4.

FIG. 1 shows a first embodiment of the present invention.

In the figure, the reference numeral 10 is the box body, and 11 is the lid.

The box body 10 has a side wall member 12 formed of a long thin plate made of zirconium or a zirconium alloy, and both longitudinal ends of the side wall members 12 are joined by brazing means or the like. In each side wall member 12, a plurality of holes 13, in this case five holes, are formed at equal intervals along the longitudinal direction to communicate the inside and outside of the box. The inside of the box body 10 that opens above and below serves as a storage space 15 for the support grid. The size of this storage space 15 is set to such an extent that the support grid can barely fit therein.

On the other hand, the lid body 11 is made of a thin plate made of zirconium or zirconium alloy like the side wall member 12, and the thin plate is formed into a square having a size that covers the support grid storage space 15 of the box body 10. This is what I did. This lid body 11
Holes 14 communicating vertically are formed in five rows vertically and horizontally at equal intervals. This hole 1
4, a lid body 11 is attached to a main body 10 in which a support grid is housed.
When covered, it is preferable that the support grid is placed at a position corresponding to the squares of the support grid.

The usage method and antioxidant effect of the getter box thus constructed will be explained.

When placing the support grid into a vacuum brazing furnace to braze each strap of the support grid, the box body 10 is placed into the vacuum brazing furnace, and the box body 1
A support grid is placed in the storage space 15 of 0, placed in the furnace, and the lid 11 is placed over the box body 10.
The getter box containing the support grid in this manner is placed in a vacuum brazing furnace.

During the brazing process, the flux contained in the brazing filler metal evaporates into oxygen-containing gas. This gas is removed to the outside of the furnace because the inside of the furnace is evacuated. At this time, some of the oxygen contained in the gas tries to be adsorbed by Al, Ti, and Nb, which have a high affinity for oxygen contained in the supporting lattice, but zirconium has a greater affinity for oxygen, so oxygen is
It is first adsorbed onto a getter box made of zirconium or a zirconium alloy, and the getter box is preferentially oxidized.

Oxygen is also effectively adsorbed by the inner peripheral surfaces of the holes 13 and 14 formed in the lid 11 and side wall member 12 of the getter box. Further, by forming these holes 13 and 14, the getter box is not filled with flux gas. For this reason, there is almost no oxygen that cannot be completely adsorbed by the getter box and remains in the box, and the supporting lattice is hardly oxidized by such oxygen.

By using a getter box in this way, oxidation of the support grid during brazing is effectively prevented, so healthy brazing can be achieved without reducing the wettability of the brazing surface. .

Furthermore, by expanding the surface area and improving air permeability by these holes 13 and 14, the heat dissipation of the getter box itself becomes good, and the heat capacity does not increase, so the support grid is not affected by the getter box. There is no possibility that the heat capacity of Therefore, the cooling effect during aging treatment will not be weakened, and there is no risk that the mechanical properties of the support grid will deteriorate.

In this embodiment, the lid 11 and the side wall member 12 are formed with undulations on their surfaces so as to have a wavy cross-sectional shape, thereby further increasing the surface area. Alternatively, a short cylindrical body made of zirconium alloy is inserted and fixed so as to protrude from the back surface of the lid body 11,
The amount of oxygen adsorption may be further increased by allowing the cylindrical body to fit into the squares of the support grid when the lid body 11 is placed on the lid body 11.

Next, a second embodiment of the present invention will be described with reference to FIG.

In the figure, reference numeral 20 indicates a getter box main body, 21 a bottom plate member, and 22 a lid body. This getter box is constructed using a tube made of zirconium or a zirconium alloy and having the same length formed into an elongated rod shape.

That is, the getter box main body 20 is constructed by assembling three pipe members 23 constituting the vertical member and two pipe members 24 constituting the horizontal member in an alternately extended manner.
Each end is joined by welding means or the like.

On the other hand, the bottom plate member 21 and the lid body 22 have the same configuration. These are the three parts that constitute the transverse member.
Two pipes 25 were arranged in parallel at equal intervals, and five pipes 26 constituting the vertical member were placed on them in parallel at equal intervals, and the intersections of the pipes 25 and 26 were joined by welding means or the like. It is something.

To use the getter box of this embodiment configured in this way, the getter box body is placed on the bottom plate member 21, a support grid is inserted inside the body, the lid body 22 is placed over the body 20, and the getter box body is placed on the bottom plate member 21. Place the whole turbo into a vacuum brazing furnace.

In this getter box, the gap 27 formed between the tubes 23 and 24 of the box body 20 and the gap 28 formed between the tubes 25 and 26 of the bottom plate member 21 and the lid 22 are These serve as the holes 13 and 14 in one embodiment.

In addition, the number of each tube material explained above is variously set depending on the size of the support grid or the outer diameter of the tube material itself.

FIG. 3 shows a third embodiment of the present invention.

In the figure, reference numeral 30 indicates a getter box body which is open at the top and bottom, and 31 is a lid.

The getter box body 30 is made by cutting a tube made of zirconium or zirconium alloy into a suitable length to form a short cylindrical body 32.
A side wall member 33 is formed by arranging a plurality of 2 in the vertical direction so that their axes are horizontal and touching each other's circumferential surfaces, and then arranging them in multiple rows in the horizontal direction and joining the parts that touch each other by welding means etc. , and is constructed by combining these side wall members 33.
In this main body 30, the inside and outside of the box are communicated through gaps 34 between the respective cylindrical bodies 32.

In addition, the lid body 31 is made of the same cylindrical body 32 as above,
They are arranged so that their axes are vertical and their circumferential surfaces are in contact with each other, and are joined by welding means or the like, and are formed in a size that is large enough to cover the inside of the main body 30. This lid body 31
In this case, when the lid body 31 is placed over the main body 30, the inside of the box is communicated with each other by gaps 35 between the cylindrical bodies 32.

In this getter box, the respective gaps 34 and 35 are different from the holes 13 and 1 in the first embodiment.
It has come to fulfill the role of 4.

FIG. 4 shows a fourth embodiment of the present invention.

In the figure, reference numeral 40 indicates a getter box body which is open at the top and bottom, and 41 is a lid.

The getter box main body 40 is constructed by combining zirconium or zirconium alloy pieces 42 formed into elongated strips into a mesh shape with a gap 43 between them, and forming a side wall member 44. It is constructed by joining both ends by welding means or the like.

The lid body 41 also includes a zirconium or zirconium alloy piece 42 as well as the side wall member 44 described above.
It is formed into a mesh shape with a size that is large enough to cover the inside of the main body 40, and has a gap 45.

In this getter box, the gap 43,
The hole 45 serves the role of the holes 13 and 14 in the first embodiment.

The method of use and operation of the second to fourth embodiments of the present invention described above are exactly the same as those of the first embodiment described above.

In addition to what has been explained above, the box body of the getter box can be made of any material as long as it has a hole that communicates the inside and outside of the box body, thereby increasing the surface area of the box body. You may.

In addition, although the box was constructed using zirconium or zirconium alloy in the present invention, Al, Ti,
If it has a greater affinity for oxygen than Nb etc.
Any metal or alloy may be used.

[Effect of the invention] As explained above, when the support grid is brazed using the getter box of the invention, the oxygen generated in the furnace is adsorbed by the getter box, and most of the support grid is oxidized. It will not be done.
Therefore, the parts to be brazed are kept clean, so that good brazing can be performed. In addition, due to the large number of pores formed in the getter box, it is possible to increase the surface area of the getter box.Furthermore, since almost no oxygen remains inside the getter box, oxygen can be removed more effectively. is adsorbed.

Further, by expanding the surface area and improving air permeability by the holes, the getter box itself has good heat dissipation properties, and its heat capacity does not increase.
Therefore, the cooling effect during aging treatment does not fade, and brazing can be performed without deteriorating the mechanical properties of the support grid.

Furthermore, since there is no need to perform pre-treatment such as plating on the surface as in the past, there is no need for additional work and labor, resulting in shorter working time and lower costs. Furthermore, since radiation source generation due to plating does not occur, the amount of radiation exposure in Plato can be reduced.

[Brief explanation of the drawing]

1 to 4 are perspective views showing the first to fourth embodiments of the present invention, respectively, and FIG. 5 is a perspective view of a support grid. 1 ... inner strap, 2 ... outer strap, 1
0, 20, 30, 40...Getz box body (box body), 13, 14...hole, 27, 28...gap (hole), 34, 35...gap (hole), 43, 45...
...Gap (hole).

Claims (1)

[Scope of utility model registration request] When brazing the support grid of a nuclear reactor fuel assembly in a vacuum furnace, the getter box that houses the support grid must contain the most oxygen of the metals contained in the alloy constituting the support grid. The box is made of a metal that has a higher affinity than the metal that has a higher affinity with Getter box for support grid brazing.