JPH02176598A - Fuel rod for nuclear reactor - Google Patents

Abstract

PURPOSE:To form an in-reactor fuel rod having necessary corrosion resistance by joining a coated tube of double structure which uses anticorrosive alloy only for its outside with an end plug which uses the same material as the anticorrosive alloy by a resistance welding means. CONSTITUTION:The coated tube 1 has the two-layered structure using the anticorrosive alloy only for the outside, the end plug 2 is made of the same material with the anticorrosive alloy, and electrodes 4 and 5 contact them respectively. A voltage E is applied between the coated tube 1 and end plug 2 to supply a current through the electrodes 4 and 5 and both the metal materials are fused and joined with heat generated on their contacting surfaces. As the anticorrosive alloy, Zircaloy 4 which is reduced in the content of, for example, tin is usable. Then, the coated tube 1 of Zircaloy 4 and the end plug 2 which is made of the same material as the alloy are joined by resistance welding to obtain the state of the two-layered structure of the fuel rod having the outer periphery of the weld zone protected by the anticorrosive alloy, and neither new alloy nor intermetallic alloy is produced to secure corrosion resistance sufficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a nuclear reactor fuel rod with improved corrosion resistance (including welded parts).

(Prior art) In recent years, as high burnup cores have been developed, corrosion of fuel cladding tubes due to cooling water has become a problem due to the longer stay in the reactor. Attempts have been made to use corrosion-resistant alloys only in the wall thickness of about 1.5%.

Due to the nature of this corrosion-resistant alloy, the main focus is on improving corrosion resistance, and therefore the strength may be low, but the problem in this case is the end plug weld.

Of course, since the stress applied to the end plug itself is small, it is possible to use the same alloy as the corrosion-resistant alloy on the outside of the cladding.
Usually, as shown in Figure 2, welding involves rotating the electrode (6) and melting the cladding tube (1) and end plug (2) with an arc (7) generated from the electrode (6), thereby bonding the joint surface. (3), so-called TIG welding is used.

(Structure to be Solved by the Invention) However, when such TIG welding is used, the entire body is melted, so the welded part is not limited to a corrosion-resistant alloy, but a new alloy or metal of a corrosion-resistant alloy and Zircaloy 4, which is the base material of the cladding tube. It becomes an intermediate compound and deteriorates corrosion resistance.

In view of the above-mentioned actual situation, an object of the present invention is to find a suitable welding method to fuse the joint surfaces that are in contact with each other without melting the whole, thereby preventing the above-mentioned deterioration of corrosion resistance. That is.

(Means for Solving the Problems) That is, the features of the present invention that meet the above objectives include a cladding tube having a two-layer structure using a corrosion-resistant alloy only for the required thickness on the outside, and a cladding made of the same material as the corrosion-resistant alloy. The end plugs are fused and joined at their joints using resistance welding means.

Here, resistance welding involves passing an electric current through an electrode between the cladding tube and the end plug, and melting and joining the two metals using the heat generated at the contact surface.

According to the research of the present inventors, it was found that it is desirable to maintain corrosion resistance by not melting the entire welded part, but by simply fusing the surfaces that are in contact with each other. Various tests were conducted to find a solution. As a result, solid-phase welding, which has recently been attracting attention, is a method that heats both joint surfaces and uses the plastic deformation to improve adhesion, but it is unbalanced in terms of equipment, and resistance welding was found to create the most desirable bonding surface.

Note that if the melting time is too long, the molten metals will mix, so it is desirable that the melting time be as short as possible.

(Function) By joining using the above-mentioned welding means, the heating generated on both joining surfaces will melt and join, and the welded part will become a corrosion-resistant alloy on the outside as well, and the new alloy or metal will be melted by melting the whole as in the conventional method. Therefore, it is possible to form a fuel rod for a nuclear reactor having the desired corrosion resistance without causing deterioration of corrosion resistance.

(Example) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows an outline of the welding means used to fabricate the fuel rod of the present invention. In the figure, (1) is a cladding tube, (2) is an end plug, (
3) is the joint surface between the two, the cladding tube (1) has a two-layer structure using a corrosion-resistant alloy only on the outside, and the end plug (2)
are made of the same material as the above-mentioned corrosion-resistant alloy, and the electrodes (4) and (5) are in contact with each other, and the cladding tube (1) and the end plug (2) are in contact with each other.
), a current is passed through the electrodes (4) and (5) to which a voltage (E) is applied, and the heat generated at the contact surface melts and joins both metals.

Here, as the above-mentioned corrosion-resistant alloy, for example, (a) Zircaloy 4 with a low soot content. (D) Zircaloy with enhanced corrosion resistance by improving heat treatment during the pipe manufacturing process 4. (c) Zirconium alloy containing niobium (NB) and the like can be mentioned. It is well known that Zircaloy 4 is a material conventionally used for light water reactor fuel cladding tubes.

Next, a Zircaloy 4 cladding tube whose outer surface was covered with each of the above corrosion-resistant alloys and an end plug made of the same material as the above alloy were joined by resistance welding. A two-layer structure protected by a corrosion-resistant alloy was obtained, no new alloys or intermetallic compounds were formed, and corrosion resistance was sufficiently maintained.

This proves that the fuel rod of the present invention has improved corrosion resistance.

(Effects of the Invention) As described above, the present invention has a two-layer cladding tube made of a corrosion-resistant alloy only on the outside, and an end plug made of the same material as the corrosion-resistant alloy, which are joined using resistance welding means. Conventional T
Unlike IG welding, the entire part does not melt (the outer periphery of the welded part is essentially protected by a corrosion-resistant alloy due to only melting due to heat generation at the joint), and a cladding tube with improved corrosion resistance is used. Even in this case, a fuel rod with improved corrosion resistance can be obtained without causing deterioration in corrosion resistance as in the conventional case.

Although the fuel rods of the present invention are particularly effective for use in high burnup cores,
Of course, this is effective in improving the corrosion resistance of all fuel rods where corrosion of the fuel cladding due to cooling water is a problem.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing how the cladding tube and end plug of a fuel rod according to the present invention are joined, and FIG. 2 is a schematic diagram showing the conventional joining state. (1)...cladding tube, (2)...end plug.

Claims (1)

[Claims] 1. A nuclear reactor fuel rod consisting of a two-layered cladding tube made of a corrosion-resistant alloy of a required thickness on the outside and an end plug made of the same material as the corrosion-resistant alloy, the joint being resistance welded. A nuclear reactor fuel rod characterized by being joined by.