JP2001220632A - Zirconium alloy with excellent corrosion resistance and low hydrogen absorption and method for producing the same - Google Patents

Abstract

[Problem] To provide a zirconium alloy suitable for a nuclear fuel cladding tube and a nuclear fuel structural member having a sufficient uniform corrosion resistance and a small hydrogen absorption amount, and a method for producing the same. SOLUTION: In mass%, Sn: 0.3 to 0.9%, F
e: 0.15 to 0.4%, Cr: 0.12% or less, N
i: 0.001 to 0.1%, Nb: 0.05 to 0.5
%, Si: 0.008 to 0.018%, N: 0.005
% And a balance of Zr and impurities and a method for producing the same.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zirconium alloy having excellent corrosion resistance and low hydrogen absorption and a method for producing the same. The alloy of the present invention is suitable for applications such as cladding tubes and structural members for nuclear fuel.

[0002]

2. Description of the Related Art A zirconium alloy used for a fuel cladding tube of a power reactor is mainly a boiling water reactor (BW).
R) applied to Zircaloy 2 (JIS-H-475)
1: ZrTN-802-D equivalent alloy) and Zircaloy 4 (JIS-H-4) applied to a pressurized water reactor (PWR)
751: ZrTN-804-D equivalent alloy). Both alloys have a long track record as fuel cladding and can be used without problems under current conditions of use.

When operating a nuclear reactor, a plurality of cladding tubes containing nuclear fuel material are bundled into a nuclear fuel assembly and inserted into a reactor core, and after reaching a certain burnup or after burning for a certain period of time, The operation of removing the fuel assembly is repeatedly performed. In recent years, high burnup (increase in the total amount of heat that can be extracted between insertion and removal of a fuel assembly) has been promoted in order to improve power generation efficiency. For this purpose, it is required to have corrosion resistance enough to withstand a prolonged residence time of the fuel assembly in the furnace and strength for sound operation in a severe environment by increasing the enrichment of nuclear fuel.

The above-mentioned zirconium alloys of Zircaloy 2 and Zircaloy 4 constituting fuel cladding tubes and fuel assemblies have excellent corrosion resistance. However, during long-term use, a reaction with high-temperature and high-pressure cooling water in a nuclear reactor causes uniform corrosion in which a black and uniform oxide film grows on the surface. In order to withstand long-term use, it is necessary to suppress this uniform corrosion, that is, the growth of the black film due to oxidation. In addition, when the base material absorbs hydrogen generated by the corrosion reaction, hydrogen embrittlement occurs and the strength is reduced. Therefore, it is necessary to suppress hydrogen absorption.

JP-A-63-33535 discloses Sn-Fe-Cr-Ni- which has excellent corrosion resistance and low hydrogen absorption.
An Nb-containing zirconium alloy is disclosed.

However, there is a concern that the corrosion resistance of this alloy may deteriorate depending on the amount of N. Further, depending on the manufacturing method, workability and corrosion resistance may be deteriorated, and the amount of hydrogen absorption may increase. JP-A-8-67954 discloses a method for producing a Sn-Fe-Cr-Ni-Nb zirconium alloy having excellent corrosion resistance. However, the zirconium alloy produced by this production method has a large amount of heat input at the time of production, so that precipitates are grown, and the workability is poor and the corrosion resistance is not sufficient. Thus, it is difficult to say that conventional zirconium alloys have sufficient corrosion resistance against high burnup of nuclear fuel and low hydrogen absorption rate, and the development of better zirconium alloys is currently desired. is there.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a fuel cell having a sufficient uniform corrosion resistance and a small hydrogen absorption amount in response to the trend of prolonging the residence time in a reactor due to the high burnup of nuclear fuel. An object of the present invention is to provide a zirconium alloy suitable for a nuclear fuel cladding tube and a nuclear fuel structural member, and a method for producing the same.

[0008]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors first reduced the uniform corrosiveness and the hydrogen absorption rate based on the chemical composition of a conventional alloy of Zircaloy 2 or Zircaloy 4. Various experiments and examinations were made on the effects of alloying elements.
As a result, the following findings were obtained.

1) The Sn content of Zircaloys 2 and 4 is 1.2 to 1.7%, but Sn has an effect of reducing the influence of N mixed as an impurity which lowers corrosion resistance. However, if Sn is contained in an amount more than necessary to reduce the adverse effect of N, the corrosion resistance is rather deteriorated.

2) To improve the corrosion resistance, the amount of N is set to 0.
If it is reduced to 005% or less, the Sn content becomes 0.3 to 0.1.
It is necessary to be in the range of 9%, and at other contents, the corrosion resistance is rather lowered.

3) When the Sn content is reduced to 0.3 to 0.9%, the strength decreases. Therefore, when Nb and Ni are added in combination, strength can be ensured, corrosion resistance is improved, and hydrogen absorption can be suppressed.

4) When a small amount of Si is contained, it is effective in improving corrosion resistance and can suppress hydrogen absorption.

5) After the solution treatment, the total heat input of the workpiece during heating and annealing before hot working is preferably adjusted to an appropriate amount, in which case the precipitation of intermetallic compounds, Since growth can be prevented, a reduction in cold workability and corrosion resistance can be more effectively suppressed.

The present invention has been made based on the above findings, and the gist is as follows.

(1) Sn: 0.3 to 0.9 in mass%
%, Fe: 0.15 to 0.4%, Cr: 0.12% or less, Ni: 0.001 to 0.1%, Nb: 0.05 to
0.5%, Si: 0.008 to 0.018%, N: 0.
A zirconium alloy containing 005% or less, the balance being Zr and impurities, having excellent corrosion resistance and low hydrogen absorption.

(2) The solution-treated material of the zirconium alloy having the chemical composition described in the above (1) is hot-worked and, if necessary, is annealed to perform cold-working at a temperature of 500 ° C. to 750 ° C. Annealing is performed once or more, and final annealing after final cold working is performed in a temperature range of 400 ° C. to 600 ° C., and is performed during heating before hot working after solution treatment and during annealing. The sum of the heat input parameters Ai obtained by the following equation is 3 × 10 ⁻²¹ to 2 ×
A method for producing a zirconium alloy, characterized in that the value is 10 ^-17 . Ai = ti × exp {−40000 / Ti} where ti: heating time before heating or annealing before i-th hot working (h) Ti: heating time before annealing and before i-th hot working At the heating temperature (K).

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for defining the chemical composition of the zirconium alloy of the present invention are described below. The following “%”
The indication is “% by mass”. Sn: Sn is effective in reducing the adverse effect of N mixed as an impurity on the corrosion resistance. In order to obtain the effect, it is necessary to contain 0.3% or more. But,
In the present invention, the N content is specified to be 0.005% or less, and it is not necessary to contain a large amount, and if it exceeds 0.9%, the corrosion resistance is impaired. Therefore, the content of Sn is 0.3 to
0.9%. Desirably, it is 0.45 to 0.8%. The cause of the deterioration of the corrosion resistance when Sn is contained in an amount more than necessary to reduce the adverse effect of N is not clear.

Fe and Cr: Fe has the effect of improving the corrosion resistance and the strength, and in particular, the effect is further enhanced by the complex addition with Cr. These effects are obtained even when the amount of Cr is as small as about 0.05%.
e is effective if added in combination with e, and the effect of Fe is 0.15
%. However, when Fe exceeds 0.4% and Cr exceeds 0.12%, the workability deteriorates, and the corrosion resistance, particularly the uniform corrosion, deteriorates conversely. Therefore, Fe is 0.15
０．４0.4%, and Cr was within a range of 0.12% or less. Desirably, Fe is 0.20 to 0.35% and Cr is 0.08%.
~ 0.12%.

Ni and Nb: Ni and Nb have an effect of improving corrosion resistance. However, although Ni improves corrosion resistance,
As the content increases, the amount of hydrogen generated by corrosion taken into the alloy increases, which tends to promote hydrogen embrittlement. On the other hand, Nb has the effect of improving corrosion resistance and suppressing hydrogen absorption. These effects indicate that even if the amount of Ni is very small, N
B is further improved when combined with b, and Nb is obtained at 0.05% or more. However, if both elements are too large, the workability is deteriorated, and the corrosion resistance and the hydrogen absorption characteristics are reduced.
Therefore, Ni is 0.001 to 0.1%, and Nb is 0.05.
-0.5%. Desirably, Ni
0.015% and Nb are 0.08 to 0.3%.

Si: Si is effective in improving uniform corrosion resistance and suppressing hydrogen absorption. However, if the content is too small or too large, the corrosion resistance and the effect of suppressing hydrogen absorption decrease. In existing Zircaloy 2 and Zircaloy 4, the content is specified as 0.012% or less as an impurity. However, in recent manufacturing techniques, the amount of Si mixed in is reduced to 0.005% or less. However, to obtain the above effect, 0.00
Requires more than 8%. On the other hand, if the content exceeds 0.018%, the effect decreases, so the upper limit is made 0.018%.
Therefore, the content of Si is set to 0.008 to 0.018%.
And Desirably, it is 0.012 to 0.015%.

N: N is an impurity and lowers the corrosion resistance, so the smaller the content, the better. When the Sn content having the effect of reducing the adverse effect of N is relatively small in the range of 0.3 to 0.9%, sufficient corrosion resistance can be obtained unless the N content is not more than 0.005%. I can't.

Next, the manufacturing method will be described.

First, an alloy element is blended into a nuclear-grade Zr sponge as a raw material, and is melted in a consumable electrode type vacuum arc melting furnace. The ingot that has been melted is forged or slab-rolled into a billet or slab, then subjected to a solution treatment, heated, hot-worked, and if necessary, annealed. afterwards,
It is preferable to perform cold working and annealing at least once or more to work to a target size, and to perform final annealing after final cold working. This cold working is cold rolling when producing a fuel cladding tube. Annealing after hot working or cold working is performed at 500 to 750 ° C. for the purpose of softening and strain relief.
In the α phase region in the temperature range of The heat treatment is performed in the α region so that the intermetallic compound precipitated beyond the solid solubility limit is not dissolved again. If the temperature is lower than 500 ° C., the strain is not completely removed, which adversely affects the next cold working.
If the temperature exceeds 300 ° C., the intermetallic compound grows and the workability deteriorates. Therefore, the annealing temperature is preferably set to 500 to 750 ° C.
However, since the final annealing performed after the final cold working is aimed at removing distortion or recrystallization of the product, 400
It is good to carry out in the range of from 600C to 600C. If the temperature is lower than 400 ° C., the corrosion resistance is poor, and if it exceeds 600 ° C., the corrosion resistance deteriorates. Therefore, the final annealing temperature is preferably 400 to 600 ° C., and it is preferable to be 550 ° C. or higher for recrystallization.

Intermetallic compounds precipitate during hot working and annealing,
To effectively prevent growth and decrease in cold workability and corrosion resistance, after solution treatment, the total heat input during heating and annealing before all subsequent hot working Is preferably as follows.

That is, when the heat input in the heating and annealing steps before the i-th hot working after the solution treatment is represented by the heat input parameter Ai shown by the following equation, the total value of the heat input parameters in each step ΣAi is preferably in the range of 3 × 10 ^-21 to 2 × 10 ^-17 .

Ai = ti × exp {−40000 / Ti} where ti: heating time before i-th hot working or heating time during annealing (h) Ti: heating time before i-th hot working And the heating temperature (K) during annealing.

Incidentally, 40000 in the formula is the active energy /
This is the value obtained from the gas constant.

When ΔAi is less than 3 × 10 ^-21 , workability is deteriorated, surface roughening during cold working may occur, leading to cracking, and furthermore, corrosion resistance may be reduced. On the other hand, if ΔAi exceeds 2 × 10 ⁻¹⁷ , the corrosion resistance may decrease, and the heat treatment is performed at a high temperature for a long time, which leads to an increase in energy cost and a decrease in productivity, which is not preferable.

[0029]

EXAMPLE Zirconium alloy 14 having the chemical composition shown in Table 1
The seed was smelted in an argon arc melting furnace. The obtained slab was subjected to a solution treatment of quenching after heating at 1050 ° C. for 30 minutes, and thereafter, a zirconium alloy plate having a thickness of 1 mm was manufactured by four manufacturing methods A to D shown in Table 2. .

The working ratios of the hot rolling were all 75%, and the working ratios of the cold rolling were all 50% for all of the first, second and third test pieces.

[0031]

[Table 1]

[Table 2] A corrosion test piece having a width of 20 mm and a length of 35 mm was cut out from these plates, the surface was wet-polished with # 600 emery paper, degreased with ethanol, and dried, and subjected to a corrosion test.

In the corrosion test, the sample was exposed to high-temperature and high-pressure water at 360 ° C. and 20 Mpa for 480 days, and the change in weight of the test piece before and after the test was weighed to determine the increase in corrosion. The corrosion increase was represented by a value when the corrosion increase of Zircaloy 4 (alloy No. 14) subjected to the test was set to 1 for comparison.

Further, the hydrogen absorption rate was determined using the test piece after the uniform corrosion test. The hydrogen absorption rate was also represented by a value when Zircaloy 4 was set to 1.

Table 3 shows the test results.

[0035]

[Table 3] As is clear from Table 3, Test Nos. 1 to 9 of the present invention examples
In Table 1, all of the corrosion increase tables are 0.6 or less, and the hydrogen absorption rates are all as low as 0.7 or less, and extremely good characteristics are obtained.

On the other hand, Test Nos. 10 to 17 of the comparative examples are alloys whose chemical compositions are out of the range specified in the present invention, but all have poor corrosion resistance. it was high.

[0037]

According to the present invention, a zirconium alloy having not only excellent corrosion resistance but also a small amount of hydrogen absorption can be obtained. It withstands irradiation environment and exhibits excellent effects as a fuel cladding tube and a nuclear fuel structural member.

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Claims (2)

[Claims] (1) Sn: 0.3 to 0.9% by mass%, F:
e: 0.15 to 0.4%, Cr: 0.12% or less, N
i: 0.001 to 0.1%, Nb: 0.05 to 0.5
%, Si: 0.008 to 0.018%, N: 0.005
% Of zirconium alloy having excellent corrosion resistance and low hydrogen absorption, the balance being Zr and impurities. 2. A solution treatment material of the zirconium alloy having the chemical composition according to claim 1, followed by hot working, annealing if necessary, and cold working at a temperature range of 500 ° C. to 750 ° C. Annealing is performed at least once, and final annealing after final cold working is performed in a temperature range of 400 ° C. to 600 ° C., in which heating and annealing before hot working after solution treatment are performed. The sum of the heat input parameters Ai obtained by the following equation is 3 × 10 ⁻²¹ to 2 × 1.
A method for producing a zirconium alloy, wherein the zirconium alloy becomes ^0-17 . Ai = ti × exp {−40000 / Ti} where ti: heating time before heating or annealing before i-th hot working (h) Ti: heating time before annealing and before i-th hot working At the heating temperature (K).