JP2830420B2 - Manufacturing method of zirconium alloy cladding tube excellent in stress corrosion cracking resistance - Google Patents

Description

The present invention relates to a zirconium (hereinafter, referred to as Zr) alloy coating that exhibits excellent resistance to stress corrosion cracking when used as a cladding tube for a nuclear reactor fuel. The present invention relates to a method for manufacturing a tube.

[Conventional technology]

It is well known that a Zr alloy cladding tube is generally used as a cladding tube for a reactor fuel. As the Zr alloy for manufacturing the Zr alloy cladding tube, Zircaloy 2 or Zircaloy 4 specified in JIS standard H4751 is used. Among them, Zircaloy tube for fuel of a pressurized water reactor is particularly preferable. 4 is used.

The Zr alloy cladding tube is manufactured by repeatedly subjecting a Zr alloy tube obtained by extrusion molding to Pilger rolling and recrystallization annealing once or a plurality of times, followed by final Pilger rolling and strain relief annealing. . The Pilger rolling is performed by cold rolling, the recrystallization annealing is performed in a vacuum atmosphere at a temperature of 530 to 760 ° C., and the final strain relief annealing is 430.
Performed at ~ 490 ° C.

The thus-obtained Zr alloy cladding tube is filled with reactor fuel pellets, assembled into a reactor fuel assembly, and inserted into the reactor core for use. The Japan Institute of Metals “Revised 5th edition Metal Handbook”
March 31, 1990, see Maruzen Co., Ltd., 812-815).

[Problems to be solved by the invention]

However, recently, as the specific gravity of nuclear power as a power supply source has increased, higher efficiency of nuclear power generation has been required, and the residence time of the reactor fuel assemblies in the reactor, the higher burnup of reactor fuel, and Furnace load following operation, etc.
Accordingly, there was a problem that the possibility of causing stress corrosion cracking of the cladding tube due to the interaction between the reactor fuel pellet and the Zr alloy cladding tube was increased.

[Means for solving the problem]

Therefore, the present inventors have solved this problem and conducted research to produce a Zr alloy clad tube having more excellent resistance to stress corrosion cracking than before. As a result, the above-mentioned Pilger rolling and recrystallization annealing were performed for 1 hour each. In the manufacturing process of the Zr alloy cladding tube which is repeated one or more times, at least one of the above-mentioned pilger rolling is performed with an outer diameter reduction rate of 1: 1.
It has been found that a Zr alloy clad tube having more excellent resistance to stress corrosion cracking can be obtained by substituting with a tensile processing of up to 30%.

The present invention has been made on the basis of such knowledge, and comprises subjecting a Zr alloy tube to repeated Pilger rolling and recrystallization annealing once or more times, respectively, followed by final Pilger rolling and strain relief annealing. In the step of manufacturing a Zr alloy cladding tube, at least one of the above-mentioned Pilger rolling is replaced by a tensile process of an outer diameter reduction rate of 1 to 30%,
The present invention is characterized by a method for producing a Zr alloy clad tube having excellent resistance to stress corrosion cracking.

In the method for producing a Zr alloy clad tube having excellent resistance to stress corrosion cracking according to the present invention, the rate of reduction in outer diameter due to the above-mentioned tensile working is 1%.
The reason for limiting the outer diameter to 30% is that if the outer diameter reduction rate is less than 1%, there is no effect on the improvement of the stress corrosion cracking resistance.
If it exceeds 30%, local deformation occurs, which is not preferable.

〔Example〕

Next, the present invention will be specifically described based on examples.

Outside diameter: 3.4 inches (86.4 mm), wall thickness: 0.6 inches (15.2 m)
m), containing Sn: 1.5% by weight, Fe: 0.2% by weight, Cr: 0.1% by weight, with the balance being Zr and unavoidable impurities.
A Zr alloy extrusion tube was prepared.

Examples 1 to 10 and Comparative Examples 1 and 2 After the above extruded raw tube was subjected to a tensile working so as to have the outer diameter reduction rate shown in Table 1, recrystallization annealing was carried out in a vacuum atmosphere. After repeating recrystallization annealing three times each in an atmosphere, final pilger rolling and strain relief annealing in a vacuum atmosphere to obtain an outer diameter of 0.374 inch (9.5 mm) and a wall thickness of 0.022 inch (0.57 m)
m) of Examples 1 to 10 and Comparative Examples 1 and 2
An alloy clad tube was manufactured. This manufacturing process is shown in Table 1 for easy understanding.

Examples 11 to 20 and Comparative Examples 3 to 4 After the above extruded raw tube was subjected to Pilger rolling and then recrystallized and annealed in a vacuum atmosphere, the outer diameter was 2.5 inches (63.5 inches).
mm) and a wall thickness of 0.43 inch (10.9 mm). An intermediate tube was manufactured, and the intermediate tube was subjected to a tensioning process to reduce the outer diameter as shown in Table 2 and then processed in a vacuum atmosphere. Then, recrystallization annealing is repeatedly performed twice each in a Pilger rolling and a vacuum atmosphere, and then final pilger rolling and a strain relief annealing in a vacuum atmosphere to obtain an outer diameter of 0.374 inches (9.5 mm). ), Wall thickness: 0.022 inch (0.57m
m) of Examples 11-20 and Comparative Examples 3-4 with dimensions of m)
An alloy clad tube was manufactured. This manufacturing process is shown in Table 2 for easy understanding.

Examples 21 to 34 and Comparative Examples 5 to 8 The above extruded raw tubes were subjected to a first tensile working so as to have an outer diameter reduction rate shown in Table 3, followed by recrystallization annealing, followed by Pilger rolling and a vacuum atmosphere. After the medium recrystallization annealing, the steel sheet was further subjected to a second tensile working so as to have the outer diameter reduction rate shown in Table 3 and then recrystallization annealing, and then subjected to Pilger rolling and recrystallization annealing in a vacuum atmosphere, respectively. After repeated application, final pilger rolling and strain relief annealing in a vacuum atmosphere to obtain an outer diameter of 0.0.
The Zr alloy cladding tubes of Examples 21 to 34 and Comparative Examples 5 to 8 having dimensions of 374 inches (9.5 mm) and wall thickness: 0.022 inches (0.57 mm) were produced. This manufacturing process is shown in Table 3 for easy understanding.

Conventional Example The above extruded raw tube is first subjected to Pilger rolling, then subjected to recrystallization annealing in a vacuum atmosphere, further subjected to Pilger rolling and recrystallization annealing three times in a vacuum atmosphere, and then subjected to final Pilger rolling. Outer diameter: 0.374 inch (9.5mm), wall thickness: 0.022 inch (0.57m)
A conventional Zr alloy cladding tube having the dimensions of m) was manufactured.
This manufacturing process is also shown in Table 3 for easy understanding.

The Zr alloy cladding tubes produced by the production methods of Examples 1 to 34, Comparative Examples 1 to 8 and the conventional example were maintained at 360 ° C., and the concentration of iodine gas as a corrosive gas was adjusted to 6.0 mg / cm ^2. And then from inside with argon gas: 28.1k
The specimen was held in a pressurized state at g / mm ² , and a stress corrosion cracking test for measuring a time until breakage was performed. The measurement results are shown in Tables 1 to 3, respectively.

In addition, about the Zr alloy cladding tube which did not lead to breakage over 72 hours, the stress corrosion cracking resistance test was stopped at that time, and it was shown in Tables 1-3 as "no breakage".

From the results shown in Tables 1 to 3, the Z-alloy cladding tubes manufactured by the manufacturing methods of Examples 1 to 34 all have a higher stress resistance than the Zr alloy cladding tubes manufactured by the conventional manufacturing method. Zr alloy cladding tubes having excellent corrosion cracking properties and produced by the production methods of Comparative Examples 1 to 8 carried out under the conditions deviating from the conditions of the present invention. The conditions indicated with an asterisk (*) are those that have insufficient stress corrosion cracking resistance and some have excellent stress corrosion cracking resistance, but these have problems with workability. It can be seen that this occurs.

〔The invention's effect〕

As described above, according to the manufacturing method of the present invention, the staying time of the reactor fuel assembly in the reactor is prolonged due to the recent improvement in the efficiency of nuclear power generation, the burnup of the reactor fuel is increased, and the load following of the reactor is followed. It is possible to provide a Zr alloy cladding tube which is less likely to cause stress corrosion cracking during operation and can be operated continuously for a long period of time.

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Claims (1)

(57) [Claims] In a process for producing a zirconium alloy cladding tube by subjecting a zirconium alloy tube to pilger rolling and recrystallization annealing once or a plurality of times, respectively, followed by final pilger rolling and strain relief annealing. A method for producing a zirconium alloy clad tube excellent in stress corrosion cracking resistance, wherein at least one of pilger rolling is replaced by a tensile process with an outer diameter reduction rate of 1 to 30%.