JP2000212663A - High corrosion resistance zirconium alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high corrosion resistance zirconium alloy combining uniform corrosion resistance and nodular corrosion resistance so as to correspond to the increase of the burnup of nuclear fuel and the prolongation of the residense time in a furnace and moreover combining high corrosion resistance-high nodular corrosion resistance small in hydrogen absorption and excellent hydrogen absorbing characteristics. SOLUTION: This zirconium alloy has a compsn. contg., by mass, 0.8 to 1.5% Sn, 0.15 to 0.35% Fe, <=0.15% Cr, 0.03 to 0.15% Ni, >0.006% to 0.018% Si, <=0.005% N, and the balance Zr with inevitable impurities, in which each content of Si, Sn and Ni also satisfies the inequality of -28<=0.33×Sn1/2-100×(Si/Ni) <=-8.5.

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, which is suitable as a cladding tube and a structural member for nuclear fuel.

[0002]

2. Description of the Related Art Zirconium alloys have a small thermal neutron absorption cross-section, are excellent in corrosion resistance, and have predetermined mechanical properties. Therefore, they are used as structural members for fuel cladding tubes of nuclear reactors and nuclear fuel assemblies. Have been.

[0003] The fuel cladding tube is filled with a nuclear fuel material and bundled and inserted into a nuclear reactor as a nuclear fuel assembly. After burning the nuclear fuel for a certain period of time, the fuel assembly is removed. The cladding tube receives neutron irradiation in the nuclear reactor and is exposed to high-temperature and high-pressure water or water vapor, so that it is required to have excellent corrosion resistance.

A typical zirconium alloy for a cladding tube is Zircaloy 2 (JIS-H-4751, ZrTN-) containing a small amount of Fe, Cr and Ni in addition to Sn.
802-D equivalent alloy) and Zircaloy 4 (JIS-H-4)
751, ZrTN-804-D equivalent alloy). These alloys are currently in operation with boiling water light water reactors (BW
R) and pressurized water reactors (PWR).

[0005] In recent years, in order to improve the power generation efficiency, the burnup of nuclear fuel has been increased in each cycle and the period of stay of fuel assemblies in the furnace has been increased, which is referred to as higher burnup. The above-mentioned zirconium alloys generally used for structural members of fuel cladding tubes and fuel assemblies have sufficient corrosion resistance during the conventional service period.

However, the higher burnup and the longer stay period in the furnace, the longer the exposure time to high-temperature and high-pressure water or steam due to more neutron irradiation, resulting in better corrosion resistance and mechanical A zirconium alloy with properties is required.

[0007] The surface of the zirconium alloy is covered with a uniform black oxide film. When the surface of the zirconium alloy is exposed to high-temperature and high-pressure water or water vapor in a nuclear reactor, this film grows little by little. Corrosion occurs.

In the BWR, a white nodular corrosion product called nodular corrosion may locally occur. The progress of corrosion reduces the thickness of the member and shortens the service life. Further, if these corrosion products are separated, the activated oxide may be mixed into the primary cooling water. Furthermore, the base material absorbs hydrogen generated by the corrosion reaction, causing hydrogen embrittlement and lowering mechanical properties.

Japanese Patent Application Laid-Open No. 8-199267 discloses Zr
A highly corrosion-resistant alloy for a nuclear reactor structural material in which the corrosion resistance to nodular corrosion is improved by reducing the content of Si as an impurity contained in a -Sn-Fe-Cr-Ni alloy to 60 ppm or less is disclosed.

Japanese Patent Application Laid-Open No. 5-214500 discloses a method for preventing the occurrence of nodular corrosion by quenching or reducing the Sn content. But,
The techniques disclosed in these publications do not improve the uniform corrosion resistance, which is regarded as important for increasing the burnup.

[0011] Zirconium in the nuclear industry (10t
h international symposium, ASTM STP 1245, 1994,
p709-723) shows that the addition of Si to a Zr-Sn-Fe-Cr alloy to increase the content reduces the uniform corrosion amount. However, this alloy has not been improved in nodular corrosion resistance and cannot be said to have sufficient corrosion resistance to cope with high burnup. Various studies have hitherto been made on the improvement of uniform corrosion properties of zirconium alloys.

[0012] For example, Japanese Patent Application Laid-Open No. 1-188643 discloses that the nitrogen content of a Zr alloy containing Sn, Fe and Cr is reduced to 0.006% or less,
A Zr alloy for a reactor fuel cladding tube having improved corrosion resistance by containing b or Ta is disclosed.

JP-A-1-191756 discloses an alloy based on Zircaloy 2 or Zircaloy 4 and further containing a small amount of Cu.

However, these alloys have been shown to have improved corrosion resistance to uniform corrosion, but not improved nodular corrosion resistance.

Thus, no alloy has simultaneously improved both the corrosion resistance to uniform corrosion and the nodular corrosion resistance.

In JP-A-63-33535, S
There is disclosed a zirconium alloy for a nuclear reactor which has nodular corrosiveness, uniform corrosiveness, and low hydrogen absorption in which Nb is added to an alloy containing n, Fe, Cr and Ni.

However, this zirconium alloy is not sufficiently resistant to uniform corrosion and nodular corrosion against high burnup and prolonged residence time of the fuel assembly in the furnace, and has a sufficient effect of suppressing hydrogen absorption. Absent.

[0018]

SUMMARY OF THE INVENTION An object of the present invention is to provide both uniform corrosion resistance and nodular corrosion resistance that can withstand high burn-up of nuclear fuel and prolonged residence time in a furnace, and furthermore, to prevent hydrogen absorption. An object of the present invention is to provide a low corrosion resistant zirconium alloy.

[0019]

The gist of the present invention relating to a high corrosion resistant zirconium alloy is as follows.

"In mass%, Sn: 0.8-1.5%, F
e: 0.15 to 0.35%, Cr: 0.15% or less, N
i: 0.03 to 0.15%, Si: more than 0.006%, 0.018% or less, N: 0.005% or less, the balance consisting of Zr and impurities, and Si, Sn
A highly corrosion-resistant zirconium alloy in which the contents of Ni and Ni satisfy the following formula:

-28 ≦ 0.33 × Sn ^1/2 -100 × (Si / Ni) ≦ -8.5 The element symbol in the formula indicates the content (% by mass) in the alloy.
The present inventors first conducted various experiments and studies to develop a zirconium alloy capable of improving uniform corrosion resistance and nodular corrosion resistance and suppressing hydrogen absorption based on the chemical composition of existing Zircaloy-2 alloy. Was done. As a result, the following findings were obtained, and the present invention was completed.

A) When the Sn content is in the range of 0.8 to 1.5% and a small amount of Si is contained, it is effective to improve both uniform corrosion resistance and nodular corrosion resistance, and Hydrogen absorption can also be suppressed.

B) The Zircaloy 2 alloy has a Sn content of 1.2 to 1.7%, but the addition of Sn is effective in reducing the effect of N which is mixed in as an impurity and lowers the corrosion resistance. . However, due to recent improvements in manufacturing technology, N
Is significantly reduced, and if Sn is contained more than necessary, the corrosion resistance deteriorates.

C) However, if Sn is too low, the strength tends to decrease.

D) The content of Si in the Zircaloy-2 alloy is specified as 0.012% or less as an impurity. However, in recent manufacturing techniques, the incorporation of Si is reduced to 0.005% or less. However, if the Si content is too low or too high, the corrosion resistance decreases and the hydrogen absorption increases.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION The reason for defining the chemical composition of the zirconium alloy of the present invention will be described in detail below. The following “%” is expressed as “% by mass”.

Sn: Sn is effective in reducing the adverse effect of N mixed as an impurity on the uniform corrosion resistance and the nodular corrosion resistance. In order to obtain the effect, the content needs to be 0.8% or more. However, in recent manufacturing techniques, the content of N has been reduced, so that it is not necessary to make the content large, and if it exceeds 1.5%, the corrosion resistance is impaired. Therefore, the content of Sn is 0.8 to 1.5%.
And Desirably, it is 0.8 to 1.35%.

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 effective if Cr is combined with Fe even if the amount of Cr is very small, and the effect of Fe can be obtained at 0.15% or more. However, if both elements are too large, the workability is deteriorated, and the corrosion resistance, particularly the uniform corrosion resistance, is deteriorated. Then, F
e is in the range of 0.15% to 0.35%, and Cr is in the range of 0.15% or less. Desirable content is 0.15-0.3 Fe.
% And Cr are 0.008 to 0.1%.

Ni: Ni is effective in improving corrosion resistance. However, as the content of Ni increases, the amount of hydrogen generated by corrosion taken into the alloy increases, which tends to promote hydrogen embrittlement. Therefore, when it is necessary to avoid hydrogen absorption like the conventional Zircaloy 4, the content should be small. If the content is less than 0.03%, there is no effect of improving the corrosion resistance. On the other hand, if it exceeds 0.15%, not only the hydrogen absorption becomes remarkable but also the workability is deteriorated, so that the Ni content is 0.03 to 0. .15%. Desirably, it is 0.07 to 0.1%.

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 incorporation of Si is reduced to 0.005% or less. However, to achieve the above effect, an amount exceeding 0.006% is required. 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 exceeds 0.006% and is 0.018%.
% Or less. Desirably, it is 0.012 to 0.018%.

The alloy of the present invention can be obtained by mixing an alloying element with a nuclear-grade Zr sponge as a raw material and melting it in a consumable electrode type vacuum arc melting furnace. Fuel cladding tubes of nuclear reactors are forged or lumped from molten ingots into slabs, subjected to solution treatment, formed into billets or slabs, hot extruded or hot rolled, and then required The quenching process is performed in accordance with the above, and cold rolling and annealing are repeated to manufacture. These manufacturing conditions and the like may be the same as those generally used.

N: N is an impurity and lowers the uniform corrosion resistance and the nodular corrosion resistance, so the smaller the content, the better. Sn having an effect of reducing the adverse effect of N
When the content of N is relatively small in the range of 0.8 to 1.5%, unless the N content is 0.005% or less,
Sufficient uniform corrosion resistance and nodular corrosion resistance cannot be obtained. -28 ≦ 0.33 × Sn ^1/2 -100 × (Si / Ni) ≦ -8.5: Sn, Si and Ni are elements that affect the amount of hydrogen absorption, and the content is within the above range and the following formula Unless the amount is satisfied, the absorption of hydrogen cannot be sufficiently suppressed.

-28 ≦ 0.33 × Sn ^1/2 -100 × (Si / Ni) ≦ −8.5 This equation is obtained by systematically analyzing various experimental results.

[0034]

EXAMPLES Alloys having the chemical compositions shown in Table 1 were melted in an argon arc melting furnace. The obtained cast slab was subjected to β treatment of heating at 1050 ° C. for 30 minutes and then rapidly cooling, and then 650 ° C.
After hot rolling and annealing at 650 ° C. for 2 hours,
Next, cold rolling and annealing at 577 ° C. for 3 hours were performed to finish a plate having a thickness of 1 mm.

From these plates, a width of 20 mm and a length of 35 m
m, and the surface was wet-polished with # 600 emery paper, degreased and dried with ethanol, and subjected to a uniform corrosion test and a nodular corrosion test.

[0036]

[Table 1]

The corrosion test was an accelerated test at 400.degree.
The test piece was exposed to steam of 0.3 MPa for 360 days, and the change in weight of the test piece before and after the test was weighed to determine the increase in corrosion, and the uniform corrosion resistance was evaluated.

FIG. 1 is a diagram showing the relationship between the determined corrosion increase and the formula defined in the present invention. Corrosion increase 190
When it is not more than mg / dm ² , it can be said that uniform corrosion is good. Further, the hydrogen absorption rate was determined using the test piece after the uniform corrosion test.

FIG. 2 shows the relationship between the determined hydrogen absorption rate and the formula defined in the present invention. When the temperature is 53
A nodular corrosion test was performed at 0 ° C. for 24 hours in water vapor at a pressure of 10.3 MPa to check for the occurrence of nodular corrosion. Table 1 also shows these results.

As is clear from Table 1 or FIG. 1, Test Nos. 1 to 10 are the alloys of the present invention, and have good uniform corrosion resistance and no nodular corrosion. On the other hand, Test Nos. 11 to 19 are alloys whose chemical compositions are out of the range specified in the present invention. However, all alloys have poor uniform corrosion resistance, and in Test No. 15, nodular corrosion occurs. Was.

The hydrogen absorption rate was represented by a value when the corrosion test piece of test number 1 was set to 1. As is clear from Table 1 or FIG. 2, the hydrogen absorption rates of the present invention examples (test numbers 1 to 10) were lower than those of the comparative examples (test numbers 11 to 19) and were good.

[0042]

Industrial Applicability The zirconium alloy of the present invention is not only excellent in uniform corrosion resistance but also excellent in nodular corrosion resistance, has a small hydrogen absorption amount, and is a furnace required for high burnup. It is an excellent alloy that can withstand the extension of the internal stay period, and exhibits excellent effects as a fuel cladding tube and a nuclear fuel structural member.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the increase in corrosion and Sn, Ni, and Si.

FIG. 2 is a diagram showing a relationship between a hydrogen absorption rate and Sn, Ni, and Si.

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Claims (1)

[Claims] (1) Sn: 0.8 to 1.5% by mass%, F:
e: 0.15 to 0.35%, Cr: 0.15% or less, N
i: 0.03 to 0.15%, Si: more than 0.006%, 0.018% or less, N: 0.005% or less, the balance consisting of Zr and impurities, and Si, Sn
A highly corrosion-resistant zirconium alloy, wherein each content of Ni and Ni satisfies the following expression. -28 ≦ 0.33 × Sn ^1/2 -100 × (Si / Ni) ≦ -8.5 The element symbol in the formula indicates the content (% by mass) in the alloy.