JPS63120291A - Fuel rod spacer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Object of the Invention) (Industrial Application Field) The present invention relates to a fuel rod spacer used in a fuel assembly.

(Prior Art) Generally, a large number of fuel assemblies are loaded in the core of a nuclear reactor, and each fuel assembly is configured by accommodating a large number of fuel rods in a channel box.

Each fuel rod contains uranium oxide or plutonium oxide, which is a nuclear fuel, in a sealed cladding tube made of zirconium alloy material. The plurality of fuel rods are arranged in a grid-like matrix within the channel box and supported by a plurality of fuel rod spacers provided in the axial direction of the fuel rods. These fuel rod spacers restrain horizontal vibration of each fuel rod and ensure a coolant flow path.

When designing such a fuel rod spacer, considerations must be made to maintain appropriate fuel rod spacing, allow for fuel rod thermal expansion, facilitate assembly of fuel rod bundles, and reduce contact with fuel rods. minimize surface area, minimize reactor coolant flow changes and restrictions, minimize thermal effects of spacers on fuel rods;
These include minimizing the absorption of derived neutrons and maintaining sufficient mechanical strength to withstand reactor conditions during operation.

Various fuel rod spacers have been proposed to meet these design requirements. A typical example thereof is shown in Japanese Patent Application Laid-Open No. 59-65287. As shown in the plan view of FIG. 4 and the partially cutaway side view of FIG. The fuel rods are arranged in an array to form a fuel rod passage 4. The cross-sectional shape of the cell 3 is approximately circular as shown in a perspective view in FIG. 6, or approximately helical as shown in a plan view in FIG. As shown in the enlarged vertical cross-sectional view of the main part of the fuel rod spacer in FIG. It is held by applying pressure.

A fuel rod spacer with such an independent cell structure is particularly advantageous in that it avoids blockage of the coolant flow path by the spacer components or reduces vertical changes in the cross-sectional shape of the cells. This suppresses large changes in the flow of coolant. As a result, pressure loss at the spacer part can be reduced, and at the same time,
The critical power of the fuel rods can be increased.

(Problems to be Solved by the Invention) When assembling such a fuel assembly, it is necessary to insert the fuel rods into the fuel rod passages of the cells from which the springs protrude. As shown in FIG. 9, which is an enlarged longitudinal sectional view of section A in FIG. 8, when the fuel rod 6 is inserted, the spring 5 deforms as shown by the solid line in the figure. When the fuel rod is inserted, the fuel rod is inserted while being subjected to a pressing force from a spring, so that a large force is required to insert the fuel rod, and the surface of the fuel rod is slightly scratched. The depth of these scratches is only a few inches deep, so it does not directly affect the performance of the fuel rod.
When the fuel assembly is loaded into the reactor core and burned, there is a possibility that the cladding becomes a core of oxidation corrosion, and the appearance is also unfavorable.

The object of the present invention has been made in consideration of the above circumstances, and is to obtain a fuel rod spacer that does not damage the surface of the fuel rods during assembly of a fuel assembly.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention includes a cell frame, a large number of cells arranged within the cell frame and into which fuel rods are inserted, and a support between the adjacent cells. In the fuel rod spacer, the spring has a spring shape that forms a fuel rod insertion hole in the spacer that is larger than the outer diameter of the fuel rod when the fuel assembly is assembled, and the A fuel rod spacer is provided, characterized in that it is made of a shape memory alloy that returns to a spring shape that applies pressing force to the rod.

(Function) With this configuration, since the fuel rod insertion hole of the spacer is secured to be larger than the outer diameter of the fuel rod when assembling the fuel assembly, the surface of the fuel rod can be maintained in good condition.

(Example) An example of the present invention will be described below with reference to FIGS. 1 to 3. In this embodiment, the same parts as those in the conventional example shown in FIGS. 4 to 9 are given the same reference numerals, and a description of the structure will be omitted.

FIG. 1 is an enlarged longitudinal cross-sectional view of a main part of a fuel rod spacer showing an embodiment of the present invention. In FIG. 1, the basic structure of the fuel rod spacer according to an embodiment of the present invention is the same as that of the conventional example, except that the spring 9 incorporated in the cell 3 is made of a shape memory alloy.

Here, shape memory alloys will be briefly explained.

Shape-memory alloys exhibit a shape-memory effect accompanying crystal transformation.6 For example, if they are formed into a straight shape at a temperature above the crystal transformation point, no matter how complex the shape is deformed at low humidity below the transformation point, It is an alloy that exhibits the property of returning to a linear shape when heated to a high temperature above its transformation point. In addition,
The transformation point temperature can be easily adjusted from minus 100 degrees to plus several 100 degrees depending on the alloy composition.

In the above configuration, the spring 9 of the fuel rod spacer is formed in advance into the original spring shape that applies a pressing force to the fuel rod 6 at a set temperature, that is, a high temperature above the transformation point. That is, the spring 9 is formed at a low temperature below the transformation point so that the fuel rod insertion hole of the fuel spacer is larger than the outer diameter of the fuel rod. The fuel assembly is made silky when the temperature is below this set temperature.

The state of the spring 9 at this time is shown in an enlarged plan view of the main part of the fuel spacer in FIG. 2(a) and a longitudinal sectional view in FIG. 2(b). As shown in FIGS. 2(a) and 2(b), the spring 9 is formed so as to form a fuel rod insertion hole larger than the outer diameter of the fuel rod 6. However, no pressing force was applied. Therefore, it is possible to prevent minute scratches on the surface of the fuel rods that occur when the fuel rods are inserted during the assembly of the fuel assembly. As a result, one of the core factors of oxidative corrosion of the cladding tube can be removed when the fuel assembly is loaded into the reactor core and burned. Furthermore, by preventing scratches, it is possible to maintain a good appearance.

Next, the state of the spring at the set temperature will be explained with reference to the enlarged plan view of the main part of the fuel spacer in FIG. 3(a) and the vertical sectional view in FIG. 3(b). In FIGS. 3(a) and 3(b), when the assembled fuel assembly is placed at the set temperature. The spring 9 returns to its original shape and begins to apply a pressing force to the fuel rod 6. When the set temperature is the reactor internal temperature, the fuel assembly can be assembled at room temperature. Further, when the set temperature is set to room temperature, it is necessary to assemble the fuel assembly in an environment where the indoor temperature is kept lower than room temperature. Here, the alloy composition of the shape memory alloy used for the spring needs to be an alloy having a crystal transformation point between the temperature at the time of assembling the fuel assembly and the set temperature.

Since the shape memory alloy is used, the fuel rods can be easily inserted into the spacers when assembling the fuel assembly, and the surfaces of the fuel rods can be maintained in good condition.

[Brief explanation of the drawing]

1 to 3 show a fuel rod spacer according to an embodiment of the present invention, FIG. 1 is an enlarged longitudinal sectional view of the main part thereof, and FIG.
a) and FIG. 2(b) are an enlarged plan view and an enlarged vertical cross-sectional view of the main part to explain the shape of the spring when the fuel assembly is assembled, and FIG. 3(a) and FIG. 3(b) are FIGS. 4 and 5 are an enlarged plan view and an enlarged vertical cross-sectional view of the main parts to explain the shape of the spring at a set temperature; FIGS. Figure 6 is a perspective view showing one shape of the cell shown in Figure 4, Figure 7 is a plan view showing another shape of the cell shown in Figure 4, and Figure 8 is an enlarged longitudinal section of the main part of Figure 5. Front view, Figure 9 is the 8th
It is an enlarged vertical cross-sectional view of part A in the figure. 1...Fuel rod spacer; 3...Cell 6...Fuel rod 9...Spring agent Patent attorney
Noriyuki Chika Yudo Hirofumi Mitsumata Figure 1 Figure 2 (of) Figure 2 (b) Figure 3 (cL) Figure 3 <b) EIB Figure 8 Figure 9

Claims (1)

[Claims] (1) In a fuel rod spacer consisting of a cell frame, a large number of cells arranged within the cell frame through which fuel rods are inserted, and a spring supported between adjacent cells, the spring is not used when assembling the fuel assembly. The spacer has a spring shape that forms a fuel rod insertion hole larger than the outer diameter of the fuel rod, and is made of a shape memory alloy that returns to its shape so as to apply a pressing force to the fuel rod at a set temperature. fuel rod spacer.