JPS60119490A - Nuclear fuel rod - 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 [Technical Field of the Invention] The present invention relates to nuclear fuel rods, and in particular to welding of a fuel cladding tube whose inner surface is lined with pure zirconium (zirconium liner fuel cladding tube) and upper and lower end plugs. This invention relates to nuclear fuel rods with improved sealing structures.

[Technical background of the invention and its problems]

FIG. 1 shows a longitudinal cross-sectional view of a conventional nuclear fuel rod. In the figure, the entire inner surface of a cylindrical fuel cladding tube 1 is lined with pure zirconium, and inside the fuel cladding tube 1 are a large number of pellet-shaped nuclear fuels made by compression molding and sintering nuclear fuel material into a cylindrical shape. 3 is loaded.

Then, a plenum spring 4 is interposed in the upper plenum part of the loaded fuel cladding tube 1, and an upper end plug 5 is installed at the upper end.
Further, a lower end plug 6 is sealed at each lower end to make the inside airtight.

By thus airtightly sealing the inside of the fuel cladding tube 1, it is possible to prevent the nuclear fuel 3 from directly reacting with the cooling water, and to prevent the fission products released by the fission reaction of the nuclear fuel 3 from being absorbed into the nuclear fuel. It is contained within the rod itself, preventing it from escaping into the cooling water. For this purpose, the fuel cladding tube 1
Zircaloy-2, Zircaloy-2, which has low neutron absorption, is tough even at relatively high temperatures, and has excellent high-temperature corrosion resistance
Zirconium alloys such as No. 4 are widely used.

Although this zirconium alloy has excellent properties such as being highly ductile and non-reactive with cooling water, the fuel cladding tube 1 made of the zirconium alloy can be There is a possibility that damage due to stress corrosion cracking may occur due to the mechanical stress effect due to the difference in the coefficient of thermal expansion of the nuclear fission product and the corrosive effect due to the corrosive products contained in the fission products. In other words, stress corrosion cracking is damage that occurs when the fuel cladding tube 1 absorbs corrosive fission products released from the nuclear fuel 3 and becomes embrittled, and stress is applied to the fuel cladding tube 1. It is considered as one of the 1 failure modes.

The fuel cladding tube 1 is a barrier for the nuclear fuel rod itself, and its damage must be prevented in order to prevent the leakage of nuclear fission products.As a measure to prevent stress corrosion cracking of the fuel cladding tube 1, , a zirconium liner fuel cladding tube 1 has been proposed. This has a liner layer 2 of pure zirconium coated on the inner peripheral surface of a zirconium alloy S tube body. This pure zirconium has a Vickers hardness of, for example, about 70 DPH, and is a softer metal compared to Zircaloy-2 (zirconium alloy), which has a Vickers hardness of about 1700 PH. In addition, the corrosive fission products are prevented from directly acting on the cladding tube body, and damage to the fuel cladding tube 1 due to stress corrosion cracking is suppressed.

However, these conventional zirconium liner fuel cladding tubes 1
When the upper and lower ends of the liner are welded and sealed by the upper and lower end plugs 5 and 6, the following problem arises due to the difference in physical properties between the zirconium alloy cladding tube body and the pure zirconium of the liner j-2. That is, since pure zirconium has a lower thermal conductivity and a higher melting point than zirconium alloys, when TIG welding the zirconium liner fuel cladding tube 1 and the upper and lower end plugs 5 and 6, pure zirconium in the liner layer 2 Since the zirconium alloy is more difficult to melt than the zirconium alloy of the cladding body, welding was incomplete. To solve this problem, it is necessary to increase the current and voltage during T welding and G welding. However, when the current and voltage are increased, even if the pure zirconium of the liner layer 2 is completely melted, the melted portion of the zirconium alloy of the cladding tube body becomes larger, and the bead formed after welding becomes very thick. As the bead diameter increases,
This may damage the spacer when assembling the vortex material assembly, or reduce the cross-sectional area of the flow path during operation, increasing the pressure drop. In this way, the conventional zirconium liner fuel cladding tube 1
The welding conditions for the upper and lower end plugs 5 and 6 were very difficult, and there was a problem with the glazing.

[Purpose of the invention]

Therefore, the present invention has been made to solve various problems in the past, and uses a fuel cladding tube whose inner surface is lined with pure zirconium (zirconium liner fuel cladding tube), thereby preventing stress corrosion cracking. The purpose is not only to be effective against damage caused by the welding process, but also to have good weldability with the upper and lower end plugs.

[Summary of the invention]

In order to achieve the above object, the present invention provides a fuel cladding tube whose inner surface is lined with pure zirconium, a nuclear fuel filled in the fuel cladding tube, and an upper portion welded to the upper and lower ends of the fuel cladding tube. , a lower end plug,
This consists in forming non-lined parts not coated with pure zirconium at the upper and lower ends of the inner surface of the fuel cladding tube.

[Embodiments of the invention]

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 2 and 3. Since the structure is the same as that of a conventional nuclear fuel rod except for the structure of the fuel cladding tube 1, In the figure, only the configuration of the main parts is shown, and the same reference numerals are given to the parts that are not different from the conventional ones.

That is, in the fuel cladding tube 1 according to the present invention, non-lined portions 7 not coated with pure zirconium are formed at the upper and lower ends of the inner surface. This non-lined part 7 is formed by machining the liner J@ after coating with pure zirconium and manufacturing.
20 by removing a predetermined portion. Further, it can be removed by chemical polishing, and furthermore, it can be formed by masking during the coating process.

At this time, the length of the non-lined portion 7 from both the upper and lower ends of the fuel cladding tube 1 is set to be greater than or equal to 80 W and less than or equal to 20 W. From the viewpoint of weldability with the upper and lower end plugs 5 and 6, it is sufficient to perform this for 7 or 8 days or more on non-lined parts, but from the viewpoint of stress corrosion cracking, which is the original purpose of the fuel cladding tube 10, It is preferable that the length of the non-lined part 7 is as short as possible, and practically the upper limit is 2.
This is because it can be said that approximately 0 days is appropriate. Furthermore, the upper and lower ends of the nuclear fuel rods themselves do not have nuclear fuel 3, or even if there is, they are low-power parts, so stress corrosion cracking of the fuel cladding tube 1 is not a problem, and there is a length of about 20 m in this part. Even if there is a non-lined portion 7, no problem arises in terms of fuel performance.

〔Effect of the invention〕

The present invention is constructed as described above, and non-lined portions 7 in which pure zirconium is not implanted are formed at the upper and lower ends of the fuel cladding tube 1, which become hot when welded with the upper and lower end plugs 5 and 6. Therefore, there is no need to consider the presence of pure zirconium during welding. Therefore, since the welded part is only the zirconium alloy of the cladding tube body, weldability is good, welding conditions can be easily set, the integrity of the welded part can be ensured, and the bead diameter can be easily controlled.

As detailed above, the present invention is not only very effective against stress corrosion cracking damage of fuel cladding tubes, but also exhibits good weldability when welding with upper and lower end plugs. However, it has the excellent effect of ensuring complete sealing and maintaining fuel integrity.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view showing a conventional nuclear fuel rod, and FIGS. 2 and 3 show an embodiment of the present invention. FIG. Figure 3 is a longitudinal sectional view of the main part. DESCRIPTION OF SYMBOLS 1...Fuel cladding tube, 2...Liner layer, 3...Nuclear fuel, 4...Solenum spring, 5...Soil end plug,
6... Lower end plug, 7... Non-lined part. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A fuel cladding tube whose inner surface is lined with pure zirconium, nuclear fuel filled in the fuel cladding tube, and upper and lower end plugs welded to the upper and lower ends of the fuel cladding tube. 1. A nuclear fuel rod comprising: a non-lined portion not coated with pure zirconium is formed at the upper and lower ends of the inner surface of the fuel cladding tube. 2. Claim 1, wherein the length of the non-lined portion is 8W or more and 201111 or less from both the upper and lower ends of the fuel cladding tube, respectively.
Nuclear fuel rods as described in section.