JPH1031086A - Manufacture of fuel rod for light water reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily manufacture a fuel rod having high corrosion resistance in a short time, and reduce cost. SOLUTION: A sheath tube is made of a zirconium alloy having a composition containing Nb between 0.4wt.% and 1.2wt.%, Sn between 0.7wt.% and 1.1wt.%, Fe between 0.08wt.% and 0.24wt.% and a remnant is Zr and unavoidable impurities, or a zirconium alloy having a composition containing Nb between 0.4wt.% and 1.2wt%, Sn between 0.7wt.% and 1.1wt.%, Fe between 0.08wt.% and 0.24wt.%, and Cr between 0.08wt.% and 0.12wt.%, and a remnant is Zr and unavoidable impurities. Then, the sheath tube is filled with pellets of uranium oxide fuel. Subsequently, both ends of the sheath tube are capped with a zirconium alloy end plug having a composition containing Sn between 1.2wt.% and 1.7wt.%, Fe between 0.18wt.% and 0.24wt.%, Cr between 0.07wt.% and 0.13wt.% (where Fe+Cr: between 0.28wt.% and 0.37wt.%) and a remnant is Zr and unavailable impurities. Then, both ends of the sheath tube are sealed by jointing the tube to the end plug through a resistance welding process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a fuel rod for a light water reactor and a fuel rod for a light water reactor manufactured by the method.

[0002]

2. Description of the Related Art In general, fuel rods for light water reactors are filled with UO ₂ fuel pellets stacked inside a cladding tube made of a zirconium alloy such as Zircaloy-2 (JIS H4751ZrNT802D) or Zircaloy-4 (JIS H4751ZrNT804D), and UO2 is loaded with a spring. ₍₂₎ Both ends of the cladding tube are sealed with end plugs so as to press the fuel pellet, and the assembly is performed by TIG welding and sealing. The width of the bead of the welded portion formed by the TIG welding is about 2 mm, and a heat affected zone having a width of about 2 mm is formed on both sides thereof.

[0003] The cladding tube before welding has a working structure,
Although the end plug has an equiaxed crystal structure, the structure of the bead and the heat-affected zone of the weld formed by TIG welding changes, and the bead is very fine because it is rapidly cooled from the liquid phase. A needle-like crystal structure is formed, and the heat-affected zone is a zirconium high-temperature stable phase β (bcc) phase or α.
Is rapidly cooled from the temperature of the region where .beta. And .beta. Are mixed, thereby changing to a structure in which an equiaxed crystal structure and a needle crystal structure are mixed.

[0004] In recent years, the specific gravity of nuclear power generation has increased as a power supply source, and accordingly, efficient operation of nuclear power plants has been required. However, efficient operation of a nuclear power plant requires high-efficiency operation of the light water reactor installed therein, and high-efficiency operation of the light water reactor improves the corrosion resistance of fuel rods filled with UO ₂ fuel in zirconium cladding. Although it was necessary to reduce the number of replacements of the fuel rods, the fuel rods using the conventional cladding tube made of Zircaloy 2 or Zircaloy 4 did not have sufficient corrosion resistance.

Therefore, (a) Nb which can withstand corrosion for a longer period than conventional Zircaloy 2 or Zircaloy 4
0.4 to 1.2% by weight, Sn: 0.7 to 1.1% by weight,
Fe: 0.08 to 0.24% by weight, the balance being Zr
And a zirconium alloy having a composition consisting of unavoidable impurities,
(B) Nb: 0.4-1.2% by weight, Sn: 0.7-
1.1% by weight, Fe: 0.08 to 0.24% by weight, C
A zirconium alloy containing r: 0.08 to 0.12% by weight and a balance of Zr and unavoidable impurities (hereinafter, these zirconium alloys are referred to as zirconium alloys containing Nb and Fe) has been proposed. JP 6
1-1170552, JP-A-1-188463, JP-A-2-4937, JP-A-3-9052
No. 7, Japanese Patent Publication No. 2-6018, Japanese Patent Publication No. 3-60
No. 19).

[0006]

A cladding tube made of a zirconium alloy containing Nb and Fe is used for TIG.
After welding, the heat-affected zone obtained by allowing the welded portion to cool as it is is easily corroded.

For example, as one of the methods for evaluating the corrosion rate occurring in a nuclear reactor outside the reactor, there is an autoclave test performed at a temperature of 360 ° C. and a pressure of about 190 atm, which is the saturated vapor pressure at that temperature. However, a fuel rod sample assembled by sealing the cladding tube made of a zirconium alloy containing Nb and Fe and an end plug made of Zircaloy 4 by TIG welding was subjected to an autoclave test under the above conditions for 120 days. The bead portion and the end plug side heat-affected zone are covered with a black oxide film like the non-welded portion, and the portion covered with the black oxide film has no problem in corrosion resistance, but contains Nb and Fe. A white oxide film was formed on the weld heat affected zone on the cladding tube side made of zirconium alloy, and it was found that the corrosion resistance of the portion where this white oxide film was generated was extremely low. Therefore, the formation of the white oxide film in the heat-affected zone on the side of the cladding tube having a small thickness causes the life of the fuel rod for a light water reactor to be greatly reduced.

[0008] Therefore, after a cladding tube made of a zirconium alloy containing Nb and Fe and an end plug made of Zircaloy 4 are subjected to TIG welding, heat treatment is performed on the heat-affected zone of the welded portion to form a white oxide film on the heat-affected zone. However, in this heat treatment, it is difficult to control the cooling rate, it takes time, and the productivity is poor.

[0009]

Therefore, the present inventors have proposed N
When research was conducted on a white oxide film generated in the heat-affected zone of a cladding tube made of a zirconium alloy containing b and Fe, the cladding tube made of a zirconium alloy containing Nb and Fe was changed to Sn: 1.2 to 1.7% by weight, F
e: 0.18-0.24% by weight, Cr: 0.07-0.
13% by weight (Fe + Cr: 0.28 to 0.37
% By weight), and the remainder is sealed with an end plug made of a zirconium alloy having a composition consisting of Zr and unavoidable impurities, and then welded to produce a fuel rod for a light water reactor. Even if heat treatment was not performed after welding, a white oxide film was not generated in the heat-affected zone of the cladding tube, and the knowledge that corrosion resistance was further improved was obtained.

The present invention has been made on the basis of such findings, and (1) Nb: 0.4 to 1.2% by weight;
Sn: 0.7 to 1.1% by weight, Fe: 0.08 to 0.2
A uranium oxide fuel pellet is filled inside a cladding tube containing zirconium alloy containing 4% by weight and the balance being Zr and unavoidable impurities, and both ends of the cladding tube are Sn:
1.2 to 1.7% by weight, Fe: 0.18 to 0.24% by weight, Cr: 0.07 to 0.13% by weight (however, Fe +
Cr: 0.28 to 0.37% by weight), with the balance being Z
(2) Nb: 0.4 A method for producing a fuel rod for a light water reactor, which is sealed with an end plug made of a zirconium alloy having a composition consisting of r and unavoidable impurities, and then sealing the clad tube and the end plug by resistance welding. ~ 1.2% by weight, Sn: 0.7
-1.1% by weight, Fe: 0.08-0.24% by weight, C
r: a uranium oxide fuel pellet is filled in a cladding tube containing 0.08 to 0.12% by weight, the balance being a zirconium alloy having a composition consisting of Zr and unavoidable impurities,
Both ends of the cladding tube are Sn: 1.2 to 1.7% by weight, Fe:
0.18 to 0.24% by weight, Cr: 0.07 to 0.13
% By weight (however, Fe + Cr: 0.28 to 0.37% by weight), the remainder being sealed with a plug made of a zirconium alloy having a composition consisting of Zr and unavoidable impurities.
A method of manufacturing a fuel rod for a light water reactor, wherein the cladding tube and the end plug are hermetically sealed by resistance welding.

[0011] The zirconium alloy containing Nb and Fe of the cladding tube used for the fuel rod for a light water reactor according to the present invention comprises Nb:
0.4 to 1.2% by weight, Sn: 0.7 to 1.1% by weight,
Fe: 0.08 to 0.24% by weight, the balance being Zr
And a composition of zirconia alloy or unavoidable impurities, Nb: 0.4 to 1.2% by weight, Sn: 0.7 to 1.
1% by weight, Fe: 0.08 to 0.24% by weight, Cr:
A zirconium alloy containing 0.08 to 0.12% by weight, with the balance being Zr and unavoidable impurities;
The end plugs for sealing both ends of the cladding tube made of a zirconium alloy containing Nb and Fe include Sn: 1.2 to 1.7% by weight, Fe: 0.18 to 0.24% by weight, and Cr: 0. 0
7 to 0.13% by weight (however, Fe + Cr: 0.28 to
0.37% by weight), and the balance is a zirconium alloy composed of a zirconium alloy having a composition composed of Zr and unavoidable impurities, and a combination thereof is most preferable.

Both ends of a cladding tube made of a zirconium alloy containing Nb and Fe are Sn: 1.2 to 1.7% by weight,
Fe: 0.18 to 0.24% by weight, Cr: 0.07 to
0.13% by weight (however, Fe + Cr: 0.28-0.
After sealing with a plug made of a zirconium alloy having a composition consisting of Zr and unavoidable impurities, and then resistance-welding the cladding tube and the plug, the welding time of resistance welding is about 0.3. The welding time is 02 seconds, which is extremely short, 1/500 of the welding time of TIG welding (about 10 seconds), and the joint by resistance welding has a joining structure close to pressure welding, and is generated by resistance welding. The heat-affected zone of the cladding is negligibly small, so the heat-affected zone created by resistance welding the ends of a zirconium alloy cladding tube containing Nb and Fe does not undergo heat treatment to change its structure. However, it is considered that no white oxide film is generated.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a fuel rod for a light water reactor according to the present invention will be described in more detail with reference to FIG. Example 1 Diameter: 10 mm, thickness: 0.6 mm, Nb:
A zirconium alloy cladding tube containing 1.0% by weight, 1.0% by weight of Sn, and 0.1% by weight of Fe and the balance of Zr and unavoidable impurities was prepared. The zirconium alloy cladding tube 1 is gripped by the chuck 3, and one end of the zirconium alloy cladding tube 1 is Sn: 1.5% by weight, F:
e: 0.2% by weight, Cr: 0.1% by weight, the remainder being sealed with a zirconium alloy end plug 2 having a composition consisting of Zr and unavoidable impurities, and pressing the end plug 2 with a push rod 5:
A pressure of 300 kg was applied to the electrode 7 while supplying helium gas into the chamber 4 from the gas inlet 6.
Resistance welding was performed at a current of 000 amperes and a current conduction time of 15 milliseconds.

The zirconium alloy cladding tube and the end plug, which were resistance-welded under the above conditions, were charged into an autoclave apparatus, and the tube was inserted into the autoclave.
An autoclave test was conducted in high-temperature pure water at 0 ° C for 120 days, and the color tone of the resistance welded part of the zirconium alloy cladding tube was examined. Since no part was observed, it was found that sufficient corrosion resistance was exhibited.

Example 2 Nb: 10 mm in diameter and 0.6 mm in thickness.
A zirconium alloy clad tube containing 1.0% by weight, 1.0% by weight of Sn, 0.1% by weight of Fe, 0.1% by weight of Cr and the balance of Zr and unavoidable impurities is prepared. The zirconium alloy cladding tube and the end plug were resistance-welded in exactly the same manner as in Example 1 except that the zirconium alloy cladding tube was used, and the resistance-welded zirconium alloy cladding tube and the end plug were connected to an autoclave device. 3
An autoclave test was performed in high-temperature pure water at 60 ° C for 120 days, and the color tone of the resistance welded part of the zirconium alloy cladding tube was examined. Since no part was observed, it was found that sufficient corrosion resistance was exhibited.

[0016]

As described above, the method of manufacturing a fuel rod for a light water reactor according to the present invention provides a fuel rod for a light water reactor having excellent corrosion resistance because it exhibits sufficient corrosion resistance without heat treatment after resistance welding. It can be easily manufactured in a shorter time than before and can reduce costs, which can greatly contribute to the development of the nuclear industry.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view for resistance welding a fuel rod for a light water reactor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Coated tube 2 End plug 3 Chuck 4 Chamber 5 Push rod 6 Gas inlet 7 Electrode

Claims (3)

[Claims] 1. Nb: 0.4 to 1.2% by weight, Sn:
A uranium oxide fuel pellet is filled inside a cladding tube made of a zirconium alloy having a composition of 0.7 to 1.1% by weight and Fe: 0.08 to 0.24% by weight, the balance being Zr and unavoidable impurities. And the both ends of the cladding tube were Sn: 1.2.
To 1.7% by weight, Fe: 0.18 to 0.24% by weight, C
r: 0.07 to 0.13% by weight (however, Fe + Cr:
0.28 to 0.37% by weight), and the remainder is sealed with an end plug made of a zirconium alloy having a composition consisting of Zr and unavoidable impurities, and then the cladding tube and the end plug are sealed by resistance welding. A method for producing a fuel rod for a light water reactor, comprising: 2. Nb: 0.4 to 1.2% by weight, Sn:
From a zirconium alloy having a composition of 0.7 to 1.1% by weight, Fe: 0.08 to 0.24% by weight, Cr: 0.08 to 0.12% by weight, with the balance being Zr and unavoidable impurities. Uranium oxide fuel pellets are filled in the cladding tube, and both ends of the cladding tube are Sn: 1.2 to 1.7% by weight, F
e: 0.18-0.24% by weight, Cr: 0.07-0.
13% by weight (Fe + Cr: 0.28 to 0.37
% By weight), the remainder being sealed with a plug made of a zirconium alloy having a composition consisting of Zr and unavoidable impurities, and then sealing the cladding tube and the plug by resistance welding. Fuel rod manufacturing method. 3. A fuel rod for a light water reactor produced by the method according to claim 1.