KR101341135B1 - Zirconium alloy having excellent mechanical properties and corrosion resistance for nuclear fuel rod cladding tube - Google Patents

Abstract

A zirconium alloy for a nuclear fuel cladding tube having excellent mechanical properties and corrosion resistance is disclosed.
Zirconium alloy for nuclear fuel cladding according to the present invention is 0.5 to 5% by weight of niobium (Nb); 0.01 to 0.35% by weight of iron (Fe); Oxygen (O) 800-3,000 ppm; 5 to 300 ppm each of at least one or more elements selected from the group consisting of silicon (Si) and phosphorus (P); And the balance zirconium (Zr).
According to the present invention, it is possible to greatly improve the corrosion resistance (corrosion resistance) without reducing mechanical properties such as tensile strength as compared with the prior art.

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, zirconium for nuclear fuel cladding having superior mechanical properties and corrosion resistance as compared to the prior art. Relates to an 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. Most widely used. The development of zircaloy-based alloys is 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 of zirconium alloys, Zirlo (Zr-1Nb-1Sn-0.2Fe) and M5 (Zr-1Nb). Alloys such as -O (<1200 ppm) have been developed and used as new fuel cladding materials. 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 endeavored to develop a new zirconium alloy having better mechanical properties and corrosion resistance that can replace the existing zircaloy-based alloys, and as a result, develop a zirconium alloy having a novel component 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 compared with the prior art.

Zirconium alloy according to an embodiment of the present invention for achieving the above object is 0.5 to 5% by weight of niobium (Nb); 0.01 to 0.35% by weight of iron (Fe); Oxygen (O) 800-3,000 ppm; 5 to 300 ppm each of at least one element selected from the group consisting of phosphorus (P) and silicon (Si); And the balance zirconium (Zr).

Zirconium alloy according to another embodiment of the present invention is 0.5 to 5% by weight of niobium (Nb); 0.01 to 0.35% by weight of iron (Fe); Oxygen (O) 800-3,000 ppm; Sulfur (S) 5 to 300 ppm; 5 to 300 ppm each of at least one or more elements selected from the group consisting of phosphorus (P) and silicon (Si); And the balance zirconium (Zr).

Zirconium alloy according to another embodiment of the present invention is niobium (Nb) 0.5 to 5% by weight; 0.01 to 0.5 wt% tin (Sn); 0.01 to 0.35% by weight of iron (Fe); Oxygen (O) 800-3,000 ppm; 5 to 300 ppm each of at least one or more elements selected from the group consisting of phosphorus (P) and silicon (Si); And the balance zirconium (Zr).

In addition, the zirconium alloy according to another embodiment of the present invention is 0.5 to 5% by weight of niobium (Nb); 0.01 to 0.5 wt% tin (Sn); 0.01 to 0.35% by weight of iron (Fe); Oxygen (O) 800-3,000 ppm; Sulfur (S) 5 to 300 ppm; 5 to 300 ppm each of at least one or more elements selected from the group consisting of phosphorus (P) and silicon (Si); And the balance zirconium (Zr).

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 according to the present invention is controlled by selecting an appropriate component of the alloy and adjusting the amount of each component added. It is possible to improve mechanical properties such as. In addition, it is possible to greatly improve the corrosion resistance (corrosion resistance) without reducing the 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 structure materials of nuclear power plants, and can improve the safety of nuclear power plants by improving mechanical properties and corrosion resistance, Improve 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 an example of the present invention,

Niobium (Nb) 0.5 to 5% by weight; 0.01 to 0.35% by weight of iron (Fe); Oxygen (O) 800-3,000 ppm; 5 to 300 ppm each of at least one element selected from the group consisting of phosphorus (P) and silicon (Si); And the balance of zirconium (Zr) or niobium (Nb) 0.5 to 5% by weight; 0.01 to 0.35% by weight of iron (Fe); Oxygen (O) 800-3,000 ppm; Sulfur (S) 5 to 300 ppm; 5 to 300 ppm each of at least one or more elements selected from the group consisting of phosphorus (P) and silicon (Si); And the balance zirconium (Zr).

In addition, the present invention may have a composition further comprising tin (Sn) in the composition. That is, the zirconium alloy according to another example of the present invention,

Niobium (Nb) 0.5 to 5% by weight; 0.01 to 0.5 wt% tin (Sn); 0.01 to 0.35% by weight of iron (Fe); Oxygen (O) 800-3,000 ppm; 5 to 300 ppm each of at least one or more elements selected from the group consisting of phosphorus (P) and silicon (Si); And residual zirconium (Zr), or 0.5 to 5 wt% of niobium (Nb); 0.01 to 0.5 wt% tin (Sn); 0.01 to 0.35% by weight of iron (Fe); Oxygen (O) 800-3,000 ppm; Sulfur (S) 5 to 300 ppm; 5 to 300 ppm each of at least one or more elements selected from the group consisting of phosphorus (P) and silicon (Si); And the balance zirconium (Zr).

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 investigation of the published literature and repeated experiments, the effects of each added element on the corrosion resistance, mechanical properties, 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 the mechanical properties and corrosion resistance by adding a small amount of elements such as silicon (Si), phosphorus (P), sulfur (S) that was not added in the existing alloy. The core of the present invention is niobium (Nb) content, which reduces the corrosion resistance by removing Sn from the alloying elements or using only a small amount of Sn, which is added to the existing alloy to increase the strength but to increase the strength. , The strength is not lowered and the corrosion resistance is increased by offsetting by the increase of all or some elements of oxygen (O) and iron (Fe) and the addition of trace amounts of elements such as silicon (Si), phosphorus (P) and sulfur (S). It is to let.

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, 0.5 to 5% by weight of niobium is used. 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 unpreferable because there is a possibility that the homogeneity and corrosion resistance of the properties may be lowered.

Tin (Sn) is known as the α phase stabilizing element of zirconium (Zr) in zirconium alloys, and serves to increase the strength in the alloy. On the other hand, when considering the corrosion resistance, it is known to reduce the content of tin. In one example of the present invention, tin is used in an amount of 0.01 to 0.5% by weight, and in another example of the present invention, tin is not included in the alloy. Even in the example of the present invention using tin, the amount of tin is controlled to be less than that of a conventionally known zirconium alloy in consideration of corrosion resistance. Niobium (Nb), oxygen (O), and iron (Nb), oxygen (O), or iron (P), silicon (Si), sulfur (S), or other elements that increase the strength instead of reducing or not using tin All or some of the alloying elements such as Fe) were increased to enhance strength.

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 used in an amount of 0.01 to 0.35% by weight. When the iron content is less than the lower limit, the effect of the above-described iron is lowered and the corrosion resistance is reduced, and the iron content exceeds the upper limit. In this case, the strength tends to increase, and workability tends to decrease, which is not preferable.

Oxygen (O) serves to enhance mechanical strength by solid solution strengthening in zirconium alloys. In the present invention, 800 to 3,000 ppm of oxygen is used, but when the oxygen content is less than the lower limit, the strength increase effect by oxygen decreases rapidly, and when the oxygen content exceeds the upper limit, the strength increases and the workability is increased. It is not preferable because it tends to be lowered.

The zirconium alloy of the present invention also contains at least one element selected from the group consisting of silicon (Si), phosphorus (P) and sulfur (S). That is, any one element of silicon (Si), phosphorus (P), and sulfur (S) may be used, and two or three elements may be used together. In the present invention, the silicon (Si), phosphorus (P), sulfur (S) is used 5 to 300ppm each. Silicon (Si) plays a role in reducing hydrogen absorption and delaying the transition rate of corrosion and enhancing strength jointly with oxygen (O). If the silicon content is less than the lower limit, it is difficult to expect the effect of improving the corrosion resistance according to the silicon content, and if the silicon content exceeds the upper limit, there is no difference in terms of the upper limit and the corrosion resistance. It is not desirable. In addition, the inventors of the present invention have found that when a small amount of phosphorus (P) is added to the zirconium alloy, strength and corrosion resistance (corrosion resistance) are improved. That is, the zirconium alloy of the present invention includes phosphorus (P), when the phosphorus content is less than the lower limit, it is difficult to expect the improvement effect of the corrosion resistance according to the addition of phosphorus, when the phosphorus content exceeds the upper limit in the case of the upper limit There is no difference in terms of corrosion resistance. In addition, a small amount of sulfur (P) may be added to the zirconium alloy according to the present invention. The inventors of the present invention have confirmed that repeated studies have shown that sulfur performs a function similar to phosphorus in a zirconium alloy. It is determined that phosphorus and sulfur perform similar functions in zirconium alloys because of similar electronic structure, atomic radius, and electronegativity, and the meaning of phosphorus content ratio is the same as that of sulfur.

Of particular note is that the effects of oxygen (O) and phosphorus (P) and the effects of oxygen (O) and sulfur (S) are interdependent. That is, the strengthening effect of oxygen is further amplified by the addition of sulfur and / or phosphorus. Therefore, unlike conventional zirconium alloys, which used a relatively large amount of tin to reinforce strength, it is possible to use only a relatively small amount even if tin is not used or tin is used. That is, the addition of sulfur and / or phosphorus may further express the strengthening effect of oxygen, it is possible to have the effect of improving the corrosion resistance sulfur and phosphorus contributes in the zirconium alloy.

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

Ingots of 200 to 300 g were prepared using vacuum arc melting equipment. 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 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

A commercially available Zr-Nb-Sn-Fe alloy (westing house) was selected as a comparative example. The component ratio of the zirconium alloy by the comparative example is described in following Table 1.

 Composition ratio of zirconium alloy division Nb
(weight%) Sn
(weight%) Fe
(weight%) O
(ppm) Si
(ppm) P
(ppm) S
(ppm) Zr Example 1 1.53 - 0.12 1,560 60 - - balance Example 2 1.54 - 0.13 1,570 - 56 - balance Example 3 1.49 - 0.13 1,590 - - 58 balance Example 4 1.51 - 0.12 1,580 - 57 59 balance Example 5 1.51 - 0.14 1510 52 - 59 balance Example 6 1.52 0.17 0.13 1,580 58 - - balance Example 7 1.51 0.16 0.12 1,560 - 58 - balance Example 8 1.52 0.17 0.12 1,590 - - 56 balance Example 9 1.50 0.16 0.13 1,580 - 58 57 balance Example 10 1.54 0.20 0.14 1600 62 - 53 balance Comparative Example 1.03 1.09 0.11 1,210 - - - balance

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.

Tensile strength was measured at a tensile rate of 10 ⁻⁴ / sec at 25 ° C. and 300 ° C.

Tensile strength measurement result division 25 ℃ measurement result (MPa) 300 ℃ measurement result (MPa) Example 1 851 492 Example 2 856 498 Example 3 843 487 Example 4 885 506 Example 5 862 498 Example 6 863 496 Example 7 883 501 Example 8 879 496 Example 9 906 523 Example 10 900 516 Comparative Example 830 478

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 to the specimens of the zirconium alloys according to the Examples and Comparative Examples were measured and the results are shown in Table 3 below.

Corrosion resistance was measured by the following method.

That is, after the specimen of the zirconium alloy according to the Examples and Comparative Examples were corroded for 100 hours and 200 hours in an oxidizing atmosphere of 300 ℃, by removing the foreign matter on the surface using Ultra sonic and the weight of the specimen with an ultra-precision microbalance Corrosion degree was quantitatively evaluated by measuring.

Weight increase measurement result division Weight gain after 100 hours
(mg / dm ㅂ) Weight increase after 200 hours
(mg / dm ㅂ) Example 1 5.3 8.2 Example 2 4.6 7.4 Example 3 6.7 9.7 Example 4 4.2 6.9 Example 5 5.1 7.1 Example 6 8.7 12.3 Example 7 7.9 10.2 Example 8 8.4 12.6 Example 9 7.6 9.9 Example 10 7.8 10.1 Comparative Example 14.4 24.3

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 (4)

Niobium (Nb) 0.5 to 5% by weight; 0.01 to 0.35% by weight of iron (Fe); Oxygen (O) 800-3,000 ppm; Phosphorus (P) 5 to 300 ppm; And the balance zirconium (Zr).
Niobium (Nb) 0.5 to 5% by weight; 0.01 to 0.35% by weight of iron (Fe); Oxygen (O) 800-3,000 ppm; Sulfur (S) 5 to 300 ppm; Phosphorus (P) 5 to 300 ppm; And the zirconium alloy, characterized in that consisting of the balance zirconium (Zr).
Niobium (Nb) 0.5 to 5% by weight; 0.01 to 0.5 wt% tin (Sn); 0.01 to 0.35% by weight of iron (Fe); Oxygen (O) 800-3,000 ppm; Phosphorus (P) 5 to 300 ppm; And the zirconium alloy, characterized in that consisting of the balance zirconium (Zr).
Niobium (Nb) 0.5 to 5% by weight; 0.01 to 0.5 wt% tin (Sn); 0.01 to 0.35% by weight of iron (Fe); Oxygen (O) 800-3,000 ppm; Sulfur (S) 5 to 300 ppm; Phosphorus (P) 5 to 300 ppm; And the balance zirconium (Zr).

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