JPS6215490A - Lattice for fuel aggregate - 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 The present invention relates to a fuel assembly grid that maintains fuel elements loaded in a nuclear reactor at regular intervals.

[Background of the invention]

A large number of fuel elements loaded into a nuclear reactor are held at regular intervals through fuel assembly grids in order to ensure coolant flow paths between the fuel elements.Such fuel assemblies Conventional examples of the fuel element holding structure of a fuel grid include, for example, Japanese Unexamined Patent Application Publication No. 59-161087 and Japanese Utility Model Application No. 59-1340.
There are those described in publications such as No. 96 and Utility Model Application Publication No. 59-134097. FIG. 5 and FIG. 1 show the basic structure of the fuel assembly grid in these conventional examples. As shown in these figures, it is equipped with support members such as a fuel assembly grid 1u, a lantern spring 31, a band protrusion 4, and a divider 5, and these support members allow the fuel elements 2 of the fuel assembly to be aligned in a predetermined position. It is supported at three points by spring pressure.

By the way, in the fuel assembly grid 1 constructed as described above, during assembly of the fuel assembly, the autoclave coating on the surface of the fuel element (the outer peripheral surface of the fuel cladding tube) comes into contact with the lantern spring 3 and the like and is scraped off.

Scratches occur in the axial and circumferential directions on the surface of the fuel element,
Local oxidation corrosion (nodular coating) near these scratches
John) were more likely to occur.

Figure 7 shows the frequency of scratches (number of scratches per 1 cm) in the axial and circumferential directions on the surface of fuel elements that occur during the assembly of such a fuel assembly, and the area rate of local oxidation corrosion (1 cm). As is clear from the figure, there was a causal relationship in which the more scratches there were on the surface of the fuel element, the more local oxidation corrosion occurred.

゛Also, since the lantern spring 3 is made of Inconel, the surface of the fuel element made of zirconium alloy (
[Object of the Invention] The present invention has been made in view of the following points, and its purpose is to prevent scratches from occurring on the autoclave coating on the surface of the fuel element. An object of the present invention is to provide a grid for a fuel assembly that can prevent the above problems and maintain the integrity of fuel elements.

[Summary of the invention]

In order to achieve the above object, the present invention provides a lattice for a fuel assembly comprising a lantern spring, a band protrusion, and a divider that support a fuel element, in which the fuel element of the lantern spring, the band protrusion, and the divider is provided. The contact surface is lined with zirconium.

According to the present invention having the above configuration, a lantern spring;
The zirconium lining the band protrusions and dividers will contact the zircaloy alloy covering the fuel element during assembly of the fuel assembly, and the zirconium may provide more protection against localized corrosion than the zircaloy alloy. Moreover, since the contact surfaces of the fuel element and the lantern spring are made of the same type of metal, electrochemical corrosion can be prevented from occurring.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

Figure 1 is a longitudinal cross-sectional view of the lantern spring in this example;
FIG. 2 shows a cross-sectional view of the band protrusion of this example, and FIG. 3 shows a vertical cross-sectional view of the divider of this example. This is also an improvement to the lantern spring etc. shown in the figure.
The same reference numerals as in the conventional example indicate the same parts. That is,
In FIG. 1, reference numeral 3 denotes a lantern spring consisting of four leaf spring pieces 3a, each of which has a lining 6 of zirconium on the outer circumferential surface of each leaf spring 3a to a suitable thickness (for example, about 50 μm).

Further, in FIG. 2, reference numeral 4 denotes a band protrusion provided inside the rod body of the fuel assembly grid 1, and the outer peripheral surface of the band protrusion 4 is lined with zirconium of about 50 μm.

Further, in FIG. 3, reference numeral 5 denotes a divider provided inside the fuel assembly lattice, and the bent top portion 5a of the divider 5 (the part that comes into contact with the fuel element) is locally lined with zirconium 6 with a thickness of about 50 μm. ing.

According to this structure, when assembling the fuel assembly, the lantern spring 3. The respective linings (zirconium) 6 of the band protrusion 4 and the divider 5 come into contact. Since the zirconium constituting each lining 6 is softer than the zircaloy alloy coating the fuel element, the autoclave coating on the surface of the fuel element is not scraped off, thereby preventing scratches from occurring on the surface of the fuel element.

Therefore, the occurrence of local oxidation corrosion caused by this can be prevented. In particular, in this embodiment, the thickness of the zirconium lining 6 was set to about 50 μm, but if the thickness is set to this level, as is clear from FIG. ), the occurrence of scratches on the surface of the fuel element can be significantly reduced.

Furthermore, since the lantern spring 3 is usually made of Inconel, conventionally there was a risk of electrochemical corrosion occurring at the contact surface between the lantern spring 3 and the fuel element, but in this example, the lantern spring 3 side Since the zirconium lining 6 and the similar metals of the zircaloy alloy covering the fuel element come into contact with each other, electrochemical corrosion can be prevented from occurring.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to prevent the occurrence of scratches on the autoclave coating on the surface of the fuel element, and furthermore to prevent the occurrence of local corrosion. Fig. 1 is a longitudinal cross-sectional view of a lantern spring in this embodiment, Fig. 2 is a cross-sectional view of a band protrusion in this embodiment, and Fig. 3 is a cross-sectional view of a band protrusion in this embodiment. Longitudinal cross-sectional view of the divider in 4th
The figure shows the relationship between the thickness of the zirconium lining and the frequency of scratches on fuel elements. Figure 5 is a plan view of a conventional fuel assembly grid. Figure 6 is a conventional fuel assembly grid supporting fuel elements. FIG. 7, a partially omitted plan view showing the structure, is a diagram showing the relationship between the frequency of occurrence of scratches on the fuel element and the area ratio where local oxidation corrosion occurs.

1... Fuel assembly grid, 2... Fuel element, 3...
・Lantern spring, 4...Band protrusion, 5...
Divider, 6... lining.

Claims (1)

[Claims] 1. In a fuel assembly lattice comprising a lantern spring, a band protrusion, and a divider that support the fuel element of the fuel assembly, zirconium is applied to the contact surfaces of the lantern spring, the band protrusion, and the divider with the fuel element. A fuel assembly lattice characterized by being lined with.