JPH10219376A - Soft zirconium alloy excellent in hydrogen absorbing characteristic and stress corrosion cracking resistance in high temperature-high pressure water vapor atmosphere - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a soft Zr alloy for a nuclear reactor material having soft mechanical properties equal to those of pure Zr while its restraint on rapid oxidation is maintained and excellent in hydrogen absorbing characteristics and stress corrosion cracking resistance in a high temp.-high pressure water vapor atmosphere by adding a specified amt. of Fe to Zr and furthermore regulating the contents of O and other inevitable impurities to specified ones. SOLUTION: In Zr, as trace additives, by weight, 0.1 to 0.6%, preferably, 0.1 to 0.4% Fe is contained, and the content of O is regulated to <=1200ppm and that of other inevitable impurities is regulated to <=2000ppm. Furthermore, for the minute regulation of its corrosion resistance, alloy elements such as Ni can be added thereto, and at this time, as for their amounts to the added, e.g. the content of Ni is preferably regulated to about 0.1 to 0.4% which is the range not deteriorating its hydrogen absorbing characteristics. In this way, while the various characteristics of the soft Zr alloy are maintained, its hydrogen absorbing characteristics and stress corrosion cracking resistance are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a zirconium alloy used for a reactor material.

[0002]

2. Description of the Related Art In general, pure zirconium has a suppressive power against rapid oxidation, but since it has low corrosion resistance when used as a reactor material, various alloying elements such as Fe, Cr, Ni, Sn and Nb are added. A zirconium alloy (Zircaloy) is used. This zircaloy has better corrosion resistance in high-temperature and high-pressure steam than pure zirconium, and is suitable for a reactor material.

[0003] Zircaloys include Zircaloy 2 and Zircaloy 4 depending on the type and amount of alloying elements to be added. Depending on the combustion conditions and the type of reactor, that is, the boiling water type or pressurized water type, etc. The most suitable type of Zircaloy is selected and used.

[0004]

However, as compared with pure zirconium, conventional zircaloy has good corrosion resistance in high-temperature and high-pressure steam, but has high mechanical strength due to the addition of alloying elements. Therefore, there is a disadvantage that the moldability is deteriorated, and it cannot be used for applications requiring soft properties.

[0005] Zircaloy obtained by adding Cr or Ni is not preferred because it easily absorbs hydrogen. Zircaloy obtained by adding only Nb has improved hydrogen absorption characteristics, but has poor mechanical strength. There is a disadvantage that it becomes unavoidable to become strong.

[0006] In addition, Zircaloy has a disadvantage that stress corrosion cracking susceptibility to iodine generated by a nuclear fission reaction in a furnace is increased, and resistance to stress corrosion cracking is relatively reduced.

The present invention has the same soft mechanical properties as pure zirconium while maintaining the ability to suppress rapid oxidation, and exhibits hydrogen absorption characteristics and stress corrosion cracking resistance in a high-temperature, high-pressure steam atmosphere. An object of the present invention is to provide an improved soft zirconium alloy.

[0008]

In order to achieve the above object,
The invention according to claim 1 includes zirconium containing 0.1 wt% or more and 0.6 wt% or less of Fe as a trace additive,
A soft zirconium alloy excellent in hydrogen absorption characteristics and stress corrosion cracking resistance in a high-temperature, high-pressure steam atmosphere characterized by having an oxygen content of 1200 ppm or less and other unavoidable impurities of 2000 ppm or less.

That is, zirconium having an oxygen content of 1200 ppm or less and other unavoidable impurities of 2000 ppm or less is used, and the alloying element contained in the zirconium is limited to Fe, and by limiting the amount thereof, rapid oxidation is performed. A soft zirconium alloy having soft mechanical properties equivalent to that of pure zirconium while maintaining the suppressing force against hydrogen, and having improved hydrogen absorption properties and stress corrosion cracking resistance in a high-temperature, high-pressure steam atmosphere.

By setting the content within such a range, not only is the hydrogen absorption property improved than that of zircaloy 2 and pure zirconium, but also the hardness from pure zirconium to hardness equivalent to zircaloy 2 is obtained. Can be selected, so that a material having an appropriate hardness can be selected according to the application.

In order to finely adjust the corrosion resistance, N
Other alloying elements such as i may be added. In this case, if added in a large amount, the hydrogen absorption characteristics are deteriorated. Therefore, it is preferable to determine the amount to be added in consideration of the balance.

The reason why the amount of Fe contained in zirconium is set to 0.1 wt% or more and 0.6 wt% or less is that if the Fe content is less than 0.1 wt%, the corrosion resistance is not sufficiently improved, and conversely, 0 wt%. If it exceeds 0.6 wt%, the mechanical strength becomes stronger than that of Zircaloy 2, which is not preferable in terms of workability, and also deteriorates the hydrogen absorption characteristics and the stress corrosion cracking resistance in a high-temperature and high-pressure steam atmosphere. is there.

According to a second aspect of the present invention, there is provided a soft zirconium alloy according to the first aspect, which is excellent in hydrogen absorption characteristics and stress corrosion cracking resistance in a high-temperature and high-pressure steam atmosphere.
The content of e is not less than 0.1 wt% and not more than 0.4 wt%.

If the Fe content in the soft zirconium alloy is less than 0.1 wt%, the corrosion resistance is not sufficiently improved, and if it exceeds 0.4 wt%, the mechanical strength becomes higher than that of pure zirconium. Therefore, in the invention of claim 2,
The amount of Fe contained in the soft zirconium alloy is 0.1 wt%
By limiting the content to 0.4 wt% or less, a soft zirconium alloy excellent in hydrogen absorption properties and stress corrosion cracking resistance in a high-temperature and high-pressure steam atmosphere having soft mechanical strength equivalent to pure zirconium is obtained.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A soft zirconium alloy (No. 1) having excellent hydrogen absorption characteristics and stress corrosion cracking resistance in a high-temperature, high-pressure steam atmosphere of the present invention in which Fe is added to sponge zirconium.
-No. Using 13), a corrosion test (corrosion resistance), measurement of Vickers hardness, and measurement of crystal grain size were performed.

In the corrosion test, soft zirconium alloys (No. 1 to No. 1) having different contents of Fe and Ni were used.
3) was molded into a test piece of 65 mm × 15 mm × 1.0 mm, and placed under high temperature and high pressure steam at 400 ° C. and 105 atm for 24 hours. The corrosion state was examined.の も の indicates that it is corrosive but can withstand as a reactor material, and X indicates that corrosion has advanced.

The Vickers hardness is an index obtained by making a test surface of a test piece of the above soft zirconium alloy with a diamond indenter, and the larger the numerical value, the higher the mechanical strength.

For comparison, pure zirconium (B)
And the content of Zircaloy-2 (P) and Fe is 0.8 w
The same test was performed for the sample of t% (No. 14). Table 1 shows the results.

[0019]

[Table 1]

As can be seen from Table 1, the alloy having a Fe content of 0.1 wt% (No. 1) has no problem in hardness, but has a corrosion resistance of ○. Fe content of 0.2 wt%
(No. 2) has a corrosion resistance of ◎, and pure zirconium (B), in other words, has no Fe, is X. Therefore, if the Fe content is less than 0.1 wt%, the corrosion resistance is Can be said to be worse.

Further, the alloy having a Fe content of 0.8 wt% (No. 14) has a corrosion resistance of ○, but is not preferable because its hardness is higher than that of Zircaloy-2 (P). Therefore, from the viewpoint of corrosion resistance, the content of Fe is preferably in the range of 0.1 wt% to 0.6 wt%.

In addition, it can be seen that the hardness of each of the alloys in which the amount of Ni added was changed for each Fe content increased as the amount of Ni added increased. The preferred reactor material is Zircaloy-2 or less.
It can be seen that it is good to set the amount of i to be 0.1 wt% or more and 0.4 wt% or less.

The grain size (ASTM) of Fe and N
It can be said that the larger the total amount of i, the larger the value. Since the crystal grain size (ASTM) is also preferably about Zircaloy-2 or less, the total addition amount of Fe and Ni may be less than 0.8 wt%.

The soft zirconium alloy of the present invention (N
o. 1 to No. 13), only Fe is added, that is, No. 13 1, No. 2, No. 6, N
o. 11 in a hydrogen gas atmosphere of 1 atm.
The sample was placed at 50 ° C. for 12 hours, and the hydrogen absorption (mg / dm ² ) was measured. For comparison, the Fe content was 0.8 w
The same test was carried out for the sample of t% (No. 14), pure zirconium (B), and zircaloy-2 (P), and the hydrogen absorption was measured. Table 2 shows the results.

[0025]

[Table 2]

From Table 2, it can be seen that zircaloy-2 absorbs a very large amount of hydrogen compared to the amount of hydrogen absorbed by pure zirconium (B).
It can be seen that the hydrogen absorption characteristics are improved irrespective of the amount of hydrogen and the hydrogen absorption is smaller than that of pure zirconium (B).

In addition, No. 2, No. 6, no. 11,
No. Using No. 14, a stress corrosion cracking test in high temperature iodine gas was performed. High temperature iodine gas with iodine partial pressure of 40
The cross-sectional reduction rate (%) at a strain rate of 10 ⁻⁵ / sec was measured for each sample using argon gas of 0 Pa at 350 ° C. For comparison, an iodine partial pressure of 0 Pa, that is, an argon gas containing no iodine at 350 ° C. was used, and the strain rate was 10 ⁻⁵ / s.
The cross-sectional reduction rate (%) at ec was measured for each sample. The result is shown in FIG.

As is evident from FIG. 1, when the Fe content is 0.6 wt% or less, the cross-sectional reduction rate is almost the same as that without any influence of iodine, but the Fe content is 0.6 wt%. %, The cross-sectional reduction rate sharply decreases. Therefore, when the content of Fe is 0.6 wt% or less, the stress corrosion cracking property in high-temperature iodine gas is improved.

[0029]

As described above, according to the present invention, by setting the Fe content to 0.1 wt% or more and 0.6 wt% or less, the hydrogen absorption property and the stress corrosion cracking resistance in a high-temperature and high-pressure steam atmosphere are obtained. It becomes a soft zirconium alloy excellent in quality.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the Fe content and the cross-sectional reduction rate when a stress corrosion cracking test was performed in a high-temperature iodine gas.

Claims (2)

[Claims] 1. A small amount additive in zirconium,
A hydrogen absorption characteristic in a high-temperature and high-pressure steam atmosphere, characterized by containing Fe of 0.1 wt% or more and 0.6 wt% or less, and having an oxygen content of 1200 ppm or less and other unavoidable impurities of 2000 ppm or less; Soft zirconium alloy with excellent stress corrosion cracking resistance. 2. The method according to claim 1, wherein the content of Fe is at least 0.1 wt% and at least 0.4 wt.
2. The soft zirconium alloy according to claim 1, which is excellent in hydrogen absorption characteristics and stress corrosion cracking resistance in a high-temperature high-pressure steam atmosphere.