KR20130116668A - Zirconium alloy having excellent mechanical properties and corrosion resistance for nuclear fuel rod cladding tube - Google Patents

Abstract

PURPOSE: A zirconium alloy for nuclear fuel jacket pipe is provided to improve mechanical properties and corrosion resistance required for the nuclear fuel jacket pipe. CONSTITUTION: A zirconium alloy for nuclear fuel jacket pipe is made of a zirconium comprising at least one component selected from a group composed of 0.2-5 wt% of Nb, 0.001-0.3 wt% of Fe, and 0.001-1 wt% of Sn; at least one component selected from a group composed 0.1-5 wt% of Ti and 0.1-5 wt% of Al; and the rest of unavoidable impurities. [Reference numerals] (AA) Amount of increased weight after 100 hours (mg/dm^2); (BB,LL) Example 1; (CC,MM) Example 2; (DD,NN) Example 3; (EE,OO) Example 4; (FF,PP) Example 5; (GG,QQ) Example 6; (HH,RR) Example 7; (II,SS) Example 8; (JJ,TT) Comparative example; (KK) Amount of increased weight after 200 hours (mg/dm^2)

Description

Zirconium alloy having excellent mechanical properties and corrosion resistance for nuclear fuel rod cladding tube

The present invention relates to an alloy material for nuclear fuel cladding, which confines nuclear fuel in a nuclear power plant nuclear reactor and prevents fission products from flowing into the cooling water. More specifically, the invention relates to a nuclear fuel cladding having superior mechanical properties and corrosion resistance as compared with the prior art. Relates to a zirconium alloy.

Zirconium alloys are widely used as nuclear fuel cladding and structural materials within the reactor core because of their low neutron absorption cross-sectional area and excellent corrosion resistance and mechanical properties. This is the most widely used. Zircaloy-based alloys are described in detail in ASTM STP-368 (p. 3-27, 1963). Zircaloy-1 (Sn: 2.5%, Zr: balance), Zircaloy-2 (Sn: 1.20-1.70%, Fe: 0.07-0.20%, Cr: 0.05-1.15%, Ni: 0.03-0.08% , O: 900-1500 ppm, Zr: residue, where (Fe + Cr + Ni): 0.16-1.70%), Zircaloy-3A (Sn: 2.5%, Fe: 0.25%, Zr: residue), Zircaloy-3B (Sn: 0.5%, Fe: 0.4%, Zr: remainder), Zircaloy-3C (Sn: 0.5%, Fe: 0.2%, Ni: 0.2%, Zr: remainder), Zircaloy-4 (Sn: 1.20- 1.70%, Fe: 0.18-0.24%, Cr: 0.07-0.13%, O: 900-1500 ppm, Ni: <0.007%, where (Fe + Cr): 0.28-0.24%) Introducing. However, alloys other than Zircaloy-2 and Zircaloy-4 could not be commercialized due to poor mechanical strength and corrosion characteristics in the furnace, and Zircaloy-4 has been used the most.

Current operating conditions of nuclear power plants are developing into situations that are difficult to overcome with conventional Zircaloy-4 fuel cladding materials. Zircaloy-based alloys are used as fuel cladding materials as the operating conditions are changed by high pH operation to increase the combustion rate, increase the operating temperature, and reduce the radiation level of the plant's primary system. This situation is difficult to use.

Under these circumstances, many nuclear fuel-related organizations have been working on new zirconium alloys that can improve the corrosion resistance and strength (mechanical properties) of zirconium alloys. Zirlo (Zr-1Nb-1Sn-0.2Fe) and Alloys such as M5 (Zr-1Nb-O (<1200 ppm)) have been developed and used as a new fuel cladding material. However, there is a constant need for a zirconium alloy for nuclear fuel cladding having excellent mechanical properties and corrosion resistance that can replace existing zircaloy alloy and new alloy cladding materials.

Accordingly, the present inventors have made efforts to develop a new zirconium alloy having better mechanical properties and corrosion resistance that can replace the existing zircal alloy alloy, and as a result, develop a zirconium alloy having a novel composition and composition ratio, and a new zirconium alloy The present invention was completed by confirming the excellent mechanical properties and corrosion resistance.

It is an object of the present invention to provide a zirconium alloy for a nuclear fuel cladding which can replace a conventional zircaloy alloy. That is, the present invention is to provide a zirconium alloy for fuel cladding with improved combination of mechanical properties and corrosion resistance required in the fuel cladding as compared to the prior art.

Zirconium alloy according to the present invention for achieving the above object,

Niobium (Nb) 0.2 to 5 weight percent; And at least one component selected from the group consisting of 0.1 to 5 wt% of titanium (Ti) and 0.1 to 5 wt% of aluminum (Al).

For example of the zirconium alloy according to the present invention, niobium (Nb) 0.2 to 5% by weight; At least one component selected from the group consisting of 0.1 to 5% by weight of titanium (Ti) and 0.1 to 5% by weight of aluminum (Al); And the balance may be made of zirconium (Zr) containing inevitable impurities.

Other examples of the zirconium alloy according to the present invention include: niobium (Nb) 0.2 to 5 wt%; At least one component selected from the group consisting of 0.001 to 0.3% by weight of iron (Fe) and 0.001 to 1% by weight of tin (Sn); At least one component selected from the group consisting of 0.1 to 5% by weight of titanium (Ti) and 0.1 to 5% by weight of aluminum (Al); And the balance may be made of zirconium (Zr) containing inevitable impurities.

In the case of the zirconium alloy according to the present invention as described above, the tensile strength of the zirconium alloy or the Zr-Nb-O-based zirconium alloy by the selection of an appropriate component constituting the alloy and control of the addition amount of each component It is possible to improve mechanical properties such as. In addition, it is possible to greatly improve the corrosion resistance without reducing mechanical properties such as tensile strength than conventional zircal alloy or Zr-Nb-Sn-based zirconium alloy. Therefore, the zirconium alloy according to the present invention can be usefully used in nuclear fuel cladding, support lattice and structural materials of nuclear power plants, and can improve the safety of nuclear power plants by improving mechanical properties and corrosion resistance, and also fuel combustion degree It will be possible to improve the operation and increase the operating cycle of nuclear power plants.

1 is a result of measuring the tensile strength according to the Examples and Comparative Examples of the present invention.
2 is a measurement result of corrosion resistance according to Examples and Comparative Examples of the present invention.

Hereinafter, the present invention will be described in detail.

The present invention provides a zirconium alloy with improved mechanical properties and corrosion resistance compared to the prior art, the zirconium alloy according to the present invention,

Niobium (Nb) 0.2 to 5 weight percent; And at least one component selected from the group consisting of 0.1 to 5 wt% of titanium (Ti) and 0.1 to 5 wt% of aluminum (Al).

That is, the present invention is to use titanium (Ti) and aluminum (Al), which was not used in the conventional zirconium alloy, in order to satisfy both mechanical properties and corrosion resistance as one of the main features.

For example of the zirconium alloy according to the present invention, niobium (Nb) 0.2 to 5% by weight; At least one component selected from the group consisting of 0.1 to 5% by weight of titanium (Ti) and 0.1 to 5% by weight of aluminum (Al); And the balance may be made of zirconium (Zr) containing inevitable impurities. In addition, the composition may further include a trace element such as oxygen (O).

Zirconium alloy according to another embodiment of the present invention, niobium (Nb) 0.2 to 5% by weight; At least one component selected from the group consisting of 0.001 to 0.3% by weight of iron (Fe) and 0.001 to 1% by weight of tin (Sn); At least one component selected from the group consisting of 0.1 to 5% by weight of titanium (Ti) and 0.1 to 5% by weight of aluminum (Al); And the balance may be made of zirconium (Zr) containing inevitable impurities. Likewise, the composition may further include a trace element such as oxygen (O).

The inventors of the present invention, in order to select the constituent elements of the zirconium alloy in the completion of the present invention, the neutron effect, manufacturing cost, processability, alloying with the zirconium which is the parent phase first. In addition, through the examination of the published literature and repeated experiments, the effects of each added element on the mechanical properties, corrosion resistance, etc. and the effect of each added element on the properties of other elements were examined closely. Based on these examination results, the addition element of the zirconium alloy of this invention was determined primarily, and the addition amount (composition ratio) of each addition element was next determined. Through this process, a zirconium alloy with improved mechanical properties and corrosion resistance was obtained.

In particular, the present invention was able to improve mechanical properties and corrosion resistance by adding a small amount of elements such as titanium (Ti) and aluminum (Al), which were not added in the existing zirconium alloy, together with niobium (Nb).

When explaining the characteristics and the ratio of the composition ratio of each element used in the zirconium alloy composition of the present invention.

Niobium (Nb) is known as the β phase stabilizing element of zirconium (Zr) in zirconium alloys. Niobium is also known to improve the hydrogen absorption and strength of alloys. In the zirconium alloy of the present invention, the niobium is used in an amount of 0.2 to 5% by weight. When the content of niobium is less than the lower limit, there is a possibility that mechanical properties such as strength may be lowered, and the content of niobium exceeds the upper limit. It is not preferable because the homogeneity and corrosion resistance of the properties may be lowered.

Titanium (Ti) is added to the zirconium alloy according to the present invention in the form of a solid solution and plays a role of improving corrosion resistance along with reinforcement of mechanical properties such as strength and creep by solid solution strengthening. In the present invention, 0.1 to 5% by weight of titanium is used, but when the content of titanium is less than the lower limit, there is a possibility that the desired effect of the present invention, that is, the effect of enhancing the mechanical properties and improving the corrosion resistance may be insignificant. Otherwise, when the content of titanium exceeds the upper limit, the workability is high due to the high strength, and the area of neutron absorbing means is increased, so that the use as a nuclear material is not preferable.

Aluminum (Al) is added to the zirconium alloy according to the present invention plays a role of improving the corrosion resistance along with the reinforcement of mechanical properties such as enhanced strength by solid solution strengthening and precipitation hardening. In the present invention, aluminum is used in an amount of 0.1 to 5% by weight. If the aluminum content is less than the lower limit, there is a possibility that the desired effect of the present invention, that is, the effect of enhancing the mechanical properties and improving the corrosion resistance, may be insignificant. Otherwise, when the aluminum content exceeds the upper limit, the strength is increased, the workability is lowered, the oxide film properties may be changed, and the area of neutron absorbing means is increased, and thus it is not preferable to be used as a nuclear material.

Tin (Sn) is known as the α phase stabilizing element of zirconium (Zr) in the zirconium alloy, and serves to increase the strength in the zirconium alloy. On the other hand, when considering corrosion resistance, it is known to reduce the content of tin. In one example of the present invention, tin was not included in the alloy, and in another example of the present invention, tin was contained in an amount of 0.001 to 1% by weight in consideration of corrosion resistance, thereby controlling the amount of tin less than that of a conventionally known zirconium alloy. . Instead of using tin or using a trace amount, the content of niobium (Nb) was adjusted to improve strength, and elements such as titanium (Ti), aluminum (Al), and iron (Fe) were used. When the content of tin is less than the lower limit, the strength reinforcing effect may be insignificant, which is not preferable. When the content of tin exceeds the upper limit, corrosion resistance may be sharply lowered, which is not preferable.

Iron (Fe) forms an intermetallic compound together with zirconium in the zirconium alloy to cause precipitation or dispersion strengthening, and has the effect of inhibiting irradiation growth by accelerating the self-diffusion of zirconium. In the present invention, iron is not included in the alloying elements or 0.001 to 0.3% by weight is used, when the iron content is less than the lower limit there is a fear that the effect of the above-described iron is lowered, the iron content exceeds the upper limit When it does, it is unpreferable since intensity | strength becomes large and workability tends to fall.

Hereinafter, the present invention will be described in more detail with reference to Examples and Test Examples.

Example: Preparation of Zirconium Alloy

Zirconium alloys having various composition ratios as described in Table 1 were prepared. Preparation of the zirconium alloy was based on the following process.

(1) Preparation of Ingot

About 300 g of an ingot was manufactured using a vacuum arc melting apparatus. Five repeated dissolutions were performed to prevent sedimentation and segregation of alloy composition.

(2) cooling after β phase solution heat treatment

Heat treatment was performed to homogenize the alloy composition in the ingot by solution treatment in the β phase region. In order to prevent oxidation, the specimen was coated with a 2 mm stainless plate, held at 1,020 ° C. for 30 minutes, and then immersed in a water bath and cooled. Next, it was sufficiently dried at 120 ° C. for 10 hours to remove moisture.

(3) hot rolling

After heating at 580 ° C. for 30 minutes, hot rolling was performed. Hot rolling was carried out at a reduction ratio of about 70% in one pass, and was washed with an acid solution after the completion of hot rolling.

(4) cold rolling and heat treatment

After the hot rolling was completed, annealing was performed at 580 ° C. for 3 hours, and then cold rolling was performed to reduce the thickness.

Next, heat treatment was performed at 570 ° C. for 2 hours, followed by secondary cold rolling.

Finally, a zirconium alloy specimen was completed by heat treatment at 570 ° C. for 3 hours.

Comparative Example

The Zr-Nb-Sn-Fe alloy currently being used commercially was selected as a comparative example. The component ratio of the zirconium alloy by the comparative example is described in following Table 1.

[Table 1] Composition ratio of zirconium alloy

The tensile strength

Tensile strength of the zirconium alloy specimens according to the Examples and Comparative Examples was measured and the results are shown in Table 2 and FIG. 1. The tensile strength was measured by the method described in ASTM E8, and measured at a tensile rate of 10 ⁻⁴ / sec at 25 ° C. and 300 ° C.

[Table 2] Tensile strength measurement results

As can be seen from the results of Table 2 and FIG. 1, it was confirmed that the Examples of the present invention had superior tensile strength values at both 25 ° C. and 300 ° C. than the Comparative Example.

Corrosion resistance

Corrosion resistance of the specimens of the zirconium alloys according to the Examples and Comparative Examples was measured and the results are shown in Table 3 and FIG. 2.

Corrosion resistance was measured by the following method.

That is, after the specimens of the zirconium alloy according to the above Examples and Comparative Examples were corroded for 100 hours and 200 hours in an oxidizing atmosphere of 300 ℃, the corrosion test specimens according to the "ASTM G2, Standard test method for corrosion tubes" standards Ultra sonic The degree of corrosion was quantitatively evaluated by removing the foreign matter from the surface by measuring the weight increase of the specimen with ultra-precision microbalance.

[Table 3] Result of weight increase

As can be seen from the results of Table 3 and Figure 2, in the case of the embodiment of the present invention, both after 100 hours and after 200 hours it was confirmed that the weight increase is less than the comparative example. That is, the alloy according to the embodiment of the present invention was confirmed to have excellent corrosion resistance compared to the conventional alloy (comparative example).

Although the present invention has been described with reference to the above-described embodiments and the accompanying drawings, other embodiments may be configured within the spirit and scope of the present invention. Therefore, the scope of the present invention is defined by the appended claims and equivalents thereof, and is not limited by the specific embodiments described herein.

Claims (3)

In a zirconium alloy for nuclear fuel cladding,
Niobium (Nb) 0.2 to 5 weight percent; And at least one component selected from the group consisting of 0.1 to 5% by weight of titanium (Ti) and 0.1 to 5% by weight of aluminum (Al).
In a zirconium alloy for nuclear fuel cladding,
Niobium (Nb) 0.2 to 5 weight percent; At least one component selected from the group consisting of 0.1 to 5% by weight of titanium (Ti) and 0.1 to 5% by weight of aluminum (Al); And zirconium alloy, characterized in that the balance consists of zirconium (Zr) containing inevitable impurities.
In a zirconium alloy for nuclear fuel cladding,
Niobium (Nb) 0.2 to 5 weight percent; At least one component selected from the group consisting of 0.001 to 0.3% by weight of iron (Fe) and 0.001 to 1% by weight of tin (Sn); At least one component selected from the group consisting of 0.1 to 5% by weight of titanium (Ti) and 0.1 to 5% by weight of aluminum (Al); And zirconium alloy, characterized in that the balance consists of zirconium (Zr) containing inevitable impurities.

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