JP2006214001A - Zirconium based alloy composite having excellent creep resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zirconium based alloy composite having an excellent creep resistance. <P>SOLUTION: The zirconium based alloy composite is finally heat-treated to have the degree of recrystallization in the range of 40 to 70% in order to improve the creep resistance. The zirconium based alloy comprises 0.8 to 1.8 wt.% niobium; 0.38 to 0.50 wt.% tin; one or more elements selected from 0.1 to 0.2 wt.% iron, 0.05 to 0.15% copper, and 0.12 wt.% chromium; 0.10 to 0.15 wt.% oxygen; 0.006 to 0.010 wt.% carbon; 0.006 to 0.010 wt.% silicon; 0.0005 to 0.0020 wt.% sulfur; and the balance zirconium. The zirconium alloy manufactured with the composition in accordance with the present invention has an excellent creep resistance compared to a conventional Zircaloy-4, and may effectively be used as a nuclear cladding tube, supporting lattice and inner structures of reactor core in the nuclear power plant utilizing a light or heavy water reactor. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a zirconium alloy composition having excellent creep resistance. More specifically, the present invention relates to niobium (Nb) that has been subjected to a final heat treatment so that the recrystallization degree is 40 to 70% in order to improve creep resistance. 0.8 to 1.8% by weight; tin (Sn) 0.38 to 0.50% by weight; and / or iron (Fe) 0.1 to 0.2% by weight; copper (Cu) 0.05 to 0 One or more elements selected from 15% by weight, chromium (Cr) 0.12% by weight; oxygen (O) 0.10 to 0.15% by weight; carbon (C) 0.006 to 0.005. The present invention relates to a zirconium alloy composition comprising: 010 wt%; silicon (Si) 0.006 to 0.010 wt%; sulfur (S) 0.0005 to 0.0020 wt%; and zirconium balance (Zr).

  Nuclear power plant nuclear fuel cladding is one of the key core components that confine nuclear fuel and prevent fission products from flowing into cooling water. The outside of the nuclear fuel cladding tube is exposed to 320 ° C. cooling water under a pressure of about 15 MPa. Since the nuclear fuel cladding tube is accompanied by deterioration of mechanical properties due to bromination and growth phenomenon due to high temperature / high pressure corrosive environment and neutron irradiation, the alloy composition is very important. Thus, zirconium-based alloys (eg, Zircaloy-4) with excellent mechanical strength, creep resistance, corrosion resistance, and thermal conductivity at low temperatures and low neutron absorption were introduced in the early 1960s. Developed and used widely until now.

  However, the existing Zircaloy-4 cladding tube will continue as a nuclear fuel cladding tube due to high burn-up, long period operation, high temperature coolant and high pH operation to improve the economic efficiency of nuclear power plants. It is a reality that is difficult to use.

  Therefore, there is a demand for a new nuclear fuel cladding tube with greatly improved damage reliability and thermal margin in order to improve the safety and economic efficiency of the nuclear reactor. Therefore, a new alloy cladding tube with improved corrosion resistance and creep resistance has been developed. Newly developed new alloys for new cladding tubes tend to add Nb by reducing or eliminating the Sn content which adversely affects corrosion resistance.

  In Patent Document 1, a zirconium alloy composition containing 96% or more of Zr (hereinafter,% means% by weight) and containing 8 to 100 ppm of sulfur to a zirconium alloy to improve corrosion resistance and creep resistance. And the manufacturing process. The alloy composition referred to in the above patent is composed of the following eight alloys while claiming a Zr alloy containing 96% or more of Zr to which 8 to 100 ppm (preferably 8 to 30 ppm) of sulfur is added. Is claimed in the dependent claims.

That is, alloy 1: Zr alloy which is Sn 1.2-1.7%, Fe 0.18-0.25%, Ni 0.05-0.15%, Cr 0.05-0.15%;
Alloy 2: Zr alloy of Sn 1.2-1.7%, Fe 0.07-0.2%, Ni 0.05-0.15%, Cr 0.05-0.15%;
Alloy 3: Zr alloy with Nb 0.7-1.3% and O 900-1600 ppm;
Alloy 4: Zr alloy with Sn 0.3-1.4%, Fe 0.4-1%, V 0.2-0.7%, O 500-1800 ppm;
Alloy 5: Zr with Nb 0.7-1.3%, Sn 0.8-1.5%, Fe 0.1-0.6%, Cr 0.01-0.2%, O 500-1800 ppm alloy;
Alloy 6: Nb 0.1-0.3%, Sn 0.7-1.25%, Fe 0.1-0.3%, Cr 0.05-0.2%, Ni 0.01-0. Zr alloy that is 02%, O 500-1800 ppm;
Alloy 7: Zr alloy that is Nb 2.2-2.8%; and Alloy 8: Sn 0.3-0.7%, Fe 0.3-0.7%, Cr 0.1-0.4% , Ni 0.01-0.04%, Si 70-120 ppm, and O 500-1800 ppm are disclosed.

  Patent Document 2 discloses the following alloy-based composition and manufacturing process in which recrystallization heat treatment is performed to limit the composition and size of precipitates to improve corrosion resistance.

  (Fe 0.03-0.25%) + (Cr, V, Nb 0.8-1.3%, Sn <2000 ppm, O 500-2000 ppm, C <100 ppm, S 3-35 ppm, Si <50 ppm Zr alloy that is at least one of

  Non-Patent Document 1 discloses that Zr-1.0% Nb and Zr-0.5% Sn-0.6% Fe-0.4%, in which sulfur is added to improve thermal creep resistance. Reference is made to V alloy, and Non-Patent Document 2 of the same magazine describes the relationship between the precipitation phase produced by adding sulfur to 850 ppm to unalloyed-Zr and the corrosion characteristics. Explains.

  In addition to the above prior art, Patent Document 3 discloses an alloy to which Nb and Fe are added in order to maintain the mechanical properties of the alloy due to Sn reduction. This alloy is 0.45-0.75% Sn (preferably 0.6%), 0.4-0.53% Fe (preferably 0.45%), 0.2-0.3% Cr (preferably 0.25%), 0.3-0.5% Nb (preferably 0.45%), 0.012-0.03% Ni (preferably 0.02%), 50 ˜200 ppm Si (preferably 100 ppm), 1000 to 2000 ppm oxygen (preferably 1600 ppm). Here, Fe / Cr = 1.5, the addition amount of Nb is determined by the addition amount of Fe that affects the hydrogen absorption, and the addition amounts of Ni, Si, C, and O are adjusted, The alloy was made to have excellent corrosion resistance and strength. In Patent Document 4, in order to improve corrosion resistance and hydrogen absorption resistance, 1.0 to 2.0% Sn, 0.07 to 0.70% Fe, 0.05 to 0.15% Cr, 0 .16 to 0.40% Ni, 0.015 to 0.30% Nb (preferably 0.015 to 0.20%), 0.002 to 0.05% Si (preferably 0.015 to 0) .05%), an alloy composition comprising 900-1600 ppm oxygen is disclosed. In Patent Document 5, the addition amount of Sn, N, and Nb is mainly adjusted, and 0 to 1.5% Sn (preferably 0.6%), 0 to 0.24% Fe (preferably 0.12). %), 0-0.15% Cr (preferably 0.10%), 0-2300 ppm N, 0-100 ppm Si (preferably 100 ppm), 0-1600 ppm oxygen (preferably 1200 ppm), 0-0 An alloy composition composed of 0.5% Nb (preferably 0.45%) is disclosed. Patent Document 6 discloses a zirconium alloy composition developed for the purpose of improving ductility, creep strength, and corrosion resistance in a neutron irradiation environment. Here, the alloy is Sn 0.8-1.2%, Fe 0.2-0.5% (preferably 0.35%), Cr 0.1-0.4% (preferably 0.8. 25%), Nb 0-0.6%, Si 50-200 (preferably 50 ppm), O 900-1800 ppm (preferably 1600 ppm), and the amount of Si added to change the hydrogen absorption and process An attempt was made to reduce the change in corrosion resistance due to the difference between the two.

  Patent Document 7 discloses a double-type (Duplex) cladding tube. This zirconium alloy has a content of 0.1 to 0.3% Sn, 0.05 to 0.2% Fe, 0.05 to 0.4% Nb, one or two in Cr and Ni, 0.03. It was composed of ~ 0.1%. Here, the content of Fe + Cr + Ni should not exceed 0.25%, and oxygen was contained in 300 to 1200 ppm. In Patent Document 8 or Patent Document 9, 0 to 0.6% Nb, 0 to 0.2% Sb, 0 to 0.2% Te,. A zirconium alloy composed of 5-1.0% Sn, 0.18-0.24% Fe, 0.07-0.13% Cr, 900-2000 ppmO, 0-70 ppm Ni, 0-200 ppmC is disclosed. . Here, it is reported that the size of the precipitate is limited to 1200 to 1800 mm, and Bi can be added up to 0.2% instead of Te or Sb. A zirconium alloy composition having similar components to this is disclosed in Patent Document 10, but this alloy contains Nb 0 to 0.6%, Mo 0 to 0.1%, Sn 1.2 to 1.70%, The composition is composed of Fe 0.07 to 0.24%, Cr 0.05 to 0.13%, Ni 0 to 0.08%, and O 900 to 1800 ppm. In Patent Document 11, Nb 0 to 0.6%, Sn 0.8 to 1.2%, Fe 0 as compositions for improving the corrosion resistance, irradiation safety, mechanical strength and creep resistance of alloys. 0.2-0.5% (preferably 0.35%), Cr 0.1-0.4% (preferably 0.25%), Si 50-200 ppm (preferably 100 ppm), O 900- A zirconium alloy that is 1800 ppm (preferably 1600 ppm) is disclosed. In Patent Document 12, as a zirconium alloy in which Nb and V are added together, Fe 0.1 to 0.35%, V 0.1 to 0.4%, O 0.05 to 0.3%, Sn 0 A composition of ˜0.25%, Nb of 0 to 0.25%, V / Fe> 0.5 and an optimal alloy manufacturing process using this composition are disclosed.

  In Patent Document 13, Nb 1.7 to 2.5%, Sn 0.5 to 2.2%, and Fe 0.04 to 1.0.0 are used in order to improve the mechanical strength and the nodular corrosion resistance of the alloy. A 0% Zr alloy was disclosed, where the Fe + Mo addition was limited to 0.2-1.0%. Patent Document 14 also discloses alloys to which Nb including Zr—Sn—Fe—V alloy is added in order to improve the nodular corrosion resistance. That is, Zr 0.25 to 1.5%, Nb 0.15 to 1.0%, an alloy composition made of Fe and Zr 0.25 to 1.5%, Nb 0.5 to 1.0%, Sn An alloy composition comprising 0.05 to 0.15% Ni was proposed. Patent Document 15 discloses a ternary alloy composed of Zr 0.2 to 2.0%, Nb 0.5 to 3.0%, Sn 900 to 2500 ppm, and O. In Patent Document 16, in order to improve corrosion resistance, ductility and strength, Nb 1 to 2.5%, Sn 0.5 to 2.0%, Mo 0.1 to 1.0%, Mo + Nb 1.5 An alloy composition of ~ 2.5% is disclosed, and a manufacturing process by a solution treatment method such as solution treatment in the α + β or β region is proposed, and Patent Document 13 also has a similar composition except that Fe is added. That is, Nb 1.7 to 2.5%, Sn 0.5 to 2.2%, Fe 0.04 to 1.0%, Mo 0.2 to 1.0%, Fe + Mo 0.2 to 1.0 % Composition is disclosed.

  Patent Literature 17, Patent Literature 18, Patent Literature 19 and Patent Literature 20 disclose Zr alloys containing 0.5 to 2.0% Sn and about 0.5 to 1.0% of other solute atoms. ing. This alloy also contains 0.09 to 0.16% oxygen. Specifically, the alloy of Patent Document 17 contains Mo, Te, a mixture thereof, or Nb—Te, Nb—Mo as solute atoms other than Sn. The alloy composition of Patent Document 18 contains Cu, Ni, Fe, and the like as solute atoms. The content was limited to 0.24 to 0.40%, and Cu was added at least 0.05%. In Patent Document 19 and Patent Document 20, Mo, Nb, Te or the like is added as a solute atom, and the amount of addition is limited to 0.5 to 1.0% as in Patent Document 17, and Bi or Bi + Sn is set to 0.5. Added at ~ 2.5%.

  In Patent Document 21, an attempt was made to develop an alloy with improved corrosion resistance by improving the conventional Zircaloy-4. However, the amount of Sn added was reduced to 0 to 0.8% and 0 to 0.3%. V and 0-1% Nb were added. At this time, the addition amount of Fe was 0.2 to 0.8%, the addition amount of Cr was 0 to 0.4%, and the addition amount of Fe + Cr + V was limited to 0.25 to 1.0%. The amount of oxygen added was 1000 to 1600 ppm. 0.8% Sn-0.22% Fe-0.11% Cr-0.14% O, 0.4% Nb-0.67% Fe-0.33% Cr-0.15% O, 0. 400% for alloys with a composition of 75% Fe-0.25% V-0.1% O or 0.25% Sn-0.2% Fe-0.15% V-0.1% O When a corrosion test was conducted in a steam atmosphere at 200 ° C. for 200 days, the corrosion amount was about 60% of Zircaloy-4 and excellent, and the tensile strength was similar to that of Zircaloy-4.

  In Patent Document 22 or Patent Document 23, the alloy components were modified with existing Zircaloy-4 in order to develop a nuclear fuel cladding material with improved corrosion resistance. That is, the amount of nitrogen was reduced to 60 ppm or less by reducing the Sn content and adding Nb to compensate for the decrease in strength due to the decrease in Sn. Specifically, Sn 0.2 to 1.15%, Fe 0.19 to 0.6% (preferably 0.19 to 0.24%), Cr 0.07 to 0.4% (preferably 0.07 to 0.13%), Nb 0.05 to 0.5%, and N ≦ 60 ppm. In Patent Document 24, Nb, Ta, V, and Mo were added to adjust the existing alloy components of Zircaloy-4. Specifically, Sn 0.2 to 0.9%, Fe 0.18 to 0.6%, Cr 0.07 to 0.4%, Nb 0.05 to 0.5%, Ta 0.01 to 0.2%, V 0.05 to 1%, Mo 0.05 to 1% A Zr alloy consisting of Even in Patent Document 25 or Patent Document 26, in a conventional Zircaloy-4 alloy component, not only Sn, Fe, Cr but also a Zr alloy in which Ta is further added and Nb is selectively added, that is, Sn 0.2-1 .15%, Fe 0.19 to 0.6% (preferably 0.19 to 0.24%), Cr 0.07 to 0.4% (preferably 0.07 to 0.13%), An alloy composition comprising Ta 0.01-0.2%, Nb 0.05-0.5%, and N ≦ 60 ppm is disclosed. Patent Document 27 also presented a Zr alloy having a composition similar to this. Specifically, Sn 0.2 to 1.7%, Fe 0.18 to 0.6%, Cr 0.07 to 0.4%, Nb 0.05 to 1.0%, and Ta 0. It consisted of 01-0.1%, N <60 ppm, and presented heat treatment variables depending on composition.

In Patent Document 28, 0.5 to 1.5% Nb, 0.9 to 1.5% Sn, 0.3 to 0.6% Fe, 0.005 to 0.2% Cr, 0.005 to 0 An alloy composition comprising 0.04% C, 0.05-0.15% O, 0.005-0.015% Si is disclosed. Here, the distance between the precipitated phases containing Sn and Fe (Zr (Nb, Fe) ₂ , Zr (Fe, Cr, Nb), (Zr, Nb) ₃ Fe) is set to 0.20 to 0.40 μm. The precipitation phase containing Fe was limited to 60% by volume of the total precipitation phase.

  In Patent Document 29, an alloy composition and a size of a precipitated phase for improving corrosion resistance are proposed. Specifically, the alloy composition is 0.5-2.0% Sn, 0.05-0.3% Fe, 0.05-0.3% Cr, 0.05-0.15% Ni, 0 0.05 to 0.2% O, 0 to 1.2% Nb and the balance Zr, and the average size of the precipitates was limited to 0.5 μm or less. In Patent Document 30, heat treatment variables introduced during hot / cold working in the α-region are presented, and Sn 0.4 to 1.7%, Fe 0.25 to 0.75%, Cr 0. A Zr alloy consisting of 05-0.30%, Ni 0-0.10%, Nb 0-1.0% was presented. Patent Document 31 includes 0.05 to 0.75% Nb and 0 to 0.02% Si in order to reduce secondary damage of the alloy due to stress corrosion cracking and hydrogen absorption at high temperatures. A Zr alloy having a double structure composed of an inner layer of Sn—Fe—Cr—Ni was presented. In Patent Document 32, in order to prevent nodular corrosion, 0.5 to 1.7% Sn, 0.1 to 0.3% Fe, 0.05 to 0.02% Cr, 0.05 to 0.2% A Zr alloy composed of Cu, 0.01 to 1.0% Nb, 0.01 to 0.20% Ni was presented. In Patent Document 33, in order to improve the workability and corrosion resistance of the alloy, Sn 0.3 to 0.7%, Fe 0.2 to 0.25%, Cr 0.1 to 0.15%, Nb 0. A Zr alloy consisting of 05-0.20% was presented.

  In Patent Document 34, in a binary alloy composed of Zr—Nb, the Nb content is limited to 1 to 2.5%, and a heat treatment temperature introduced during the manufacturing process of the alloy is presented. Here, the second phase containing Nb must be uniformly distributed, and the size thereof must be maintained at 800 cm or less. Patent Document 35 presents an alloy having 0.07 to 0.28% of one or more of 0.5 to 2.0% Nb, 0.7 to 1.5% Sn, Fe, Ni, and Cr. The creep characteristics of the material can be adjusted using many manufacturing processes. Here, one of the features of the manufacturing process is to introduce β-quenching heat treatment in the middle stage.

  As described above, research has been conducted on zirconium alloys in various directions such as Zircaloy-4. However, the current nuclear power plant has severe operating conditions to improve economic efficiency, and the conventional nuclear fuel cladding tube manufactured with Zircaloy-4 or the like has reached the limit of use and is more excellent. It is necessary to develop new zirconium alloys with high creep resistance.

In view of the above, the present inventors have intensively researched to develop a new zirconium alloy with better creep resistance, while the zirconium alloy having a new composition in which the recrystallization degree is appropriately adjusted. As a result, it was found that the creep resistance of the zirconium alloy can be improved, thereby completing the present invention.
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  The present invention minimizes the creep deformation that occurs during operation when used for nuclear fuel cladding and core component materials in light water reactors and heavy water reactor nuclear power plants, doubling safety and economy over existing conventional materials. The object is to provide a zirconium alloy having excellent creep resistance.

  To achieve the above object, the present invention provides niobium (Nb) 0.8-1.8 wt%; tin (Sn) 0.38-0.50 wt%; and / or iron (Fe) 0.1 One or more elements selected from -0.2 wt%, copper (Cu) 0.05-0.15 wt%, chromium (Cr) 0.12 wt%; oxygen (O) 0.10 0.15 wt%; carbon (C) 0.006 to 0.010 wt%; silicon (Si) 0.006 to 0.010 wt%; sulfur (S) 0.0005 to 0.0020 wt%; and zirconium A zirconium alloy composition comprising the balance (Zr) is provided.

The present invention will be described in detail below.
The present invention includes a zirconium alloy composition.

  The zirconium alloy composition of the present invention preferably comprises 0.8 to 1.8 wt% niobium; 0.05 to 0.15 wt% copper; 0.10 to 0.15 wt% oxygen; 0.006 to carbon 0.010 wt%; silicon 0.006 to 0.010 wt%; sulfur 0.0005 to 0.0020 wt%; and zirconium balance.

  Further, the zirconium alloy composition of the present invention comprises niobium 0.8 to 1.8% by weight; tin 0.38 to 0.50% by weight; oxygen 0.10 to 0.15% by weight; carbon 0.006 to 0%. 0.010% by weight; silicon 0.006-0.010% by weight; sulfur 0.0005-0.0020% by weight; and zirconium balance.

  In the zirconium alloy composition of the present invention, the composition comprises niobium 0.8 to 1.8 wt%; tin 0.38 to 0.50 wt%; oxygen 0.10 to 0.15 wt%; carbon 0.006 -0.010 wt%; silicon 0.006-0.010 wt%; sulfur 0.0005-0.0020 wt%; and iron 0.1-0.2 wt% in addition to the composition containing zirconium balance, copper One or more elements selected from 0.05 to 0.15% by weight and chromium 0.12% by weight may be further included, iron 0.1 to 0.2% by weight, copper 0.05 to 0% More preferably, it further comprises one or more elements selected from 15% by weight and 0.12% by weight chromium.

  In the zirconium alloy composition of the present invention, creep resistance is improved by using the above-described zirconium alloy composition in which the recrystallization degree is maintained within the range of 40 to 70% by optimally adjusting the final vacuum heat treatment conditions. Zirconium alloys with very good properties can be produced.

  Hereinafter, the role of each alloy element used in the alloy composition of the present invention and the reason for limiting the composition ratio will be described in detail.

  Niobium (Nb) serves to improve the corrosion resistance of the zirconium alloy. However, when the solid solubility (about 0.3 to 0.6%) or more is added, the corrosion resistance can be improved by always controlling the composition and size of the precipitate. It is known that if Nb is added at a solid solubility or higher, the mechanical properties by precipitation strengthening are also good. However, when the Nb concentration is high and a large amount of precipitates are formed, the alloy performance is very sensitive to heat treatment conditions. Therefore, in the present invention, the Nb content is preferably limited to 1.8% by weight or less, and is preferably contained in the range of 0.8 to 1.8% by weight.

  Tin (Sn) is known as an α-phase stabilizing element in a zirconium alloy, and acts to improve mechanical strength by solid solution strengthening. However, if Sn is not added at all, a very rapid acceleration phenomenon appears under LiOH corrosion conditions. Therefore, in the present invention, Sn is preferably contained in the range of 0.38 to 0.50% by weight, which is controlled by the Nb content and does not significantly affect the corrosion resistance reduction.

  Iron (Fe) is a main element added to improve the corrosion resistance of the alloy. In the present invention, it is preferably added in the range of 0.05 to 0.2% by weight, but 0.1 to 0.2% by weight. It is more preferable to contain in the range of%.

  Chromium (Cr) is the main element that increases the corrosion resistance of the alloy like Fe, and the preferred Cr content in the present invention is in the range of 0.05 to 0.2% by weight, and is contained at 0.12% by weight. More preferably.

  Copper (Cu), like Fe and Cr, is a main element added for improving the corrosion resistance of the alloy, and is particularly effective when added in a trace amount. Therefore, in the present invention, it is limited to the range of 0.05 to 0.2% by weight, but it is more preferable to contain it in the range of 0.05 to 0.15% by weight.

  Oxygen (O) plays a role of contributing to improvement of mechanical strength and creep resistance by solid solution strengthening. However, if an excessive amount is added, processing problems are caused. Therefore, in the present invention, it is preferably contained in the range of 1000 to 1500 ppm (0.1 to 0.15% by weight).

  Carbon (C) and silicon (Si) reduce the hydrogen absorption and delay the transition time of the corrosion rate. Moreover, it is preferable to contain in the range of 60-100 ppm (0.006-0.010 weight%) with the impurity element relevant to corrosion resistance.

  Sulfur (S) is an impurity element that contributes to the improvement of creep resistance without affecting the corrosion characteristics at 30 ppm or less. If sulfur is added in an amount of 0.0020% by weight or more, the amount of creep deformation does not decrease any more. Therefore, it is preferable to contain S added in order to improve creep resistance in the present invention in a range of 6 to 20 ppm (0.0006 to 0.0020 wt%).

  The zirconium alloy having excellent creep resistance according to the present invention can be produced by adjusting the recrystallization degree to a range of 40 to 70%.

  The zirconium alloy having excellent creep resistance according to the present invention can be produced by a conventional method in the field of the present invention. More preferably, after performing β-heat treatment and cold working, the recrystallization degree is 40 to 40. The final heat treatment can be performed while adjusting to 70%.

  The detailed manufacturing method of the zirconium alloy composition of the present invention includes the step of forging each zirconium alloy ingot having the composition of the present invention in the β region to destroy the ingot structure; Β-quenching process in which solution heat treatment is performed in the β region and then rapidly cooled, and the β-quenching process is performed by uniformly distributing precipitates in the base metal. A step of hot rolling the β-quenched material; a step of performing a vacuum heat treatment between four cold working operations and a recrystallization degree; It consists of a step of performing the final vacuum heat treatment while adjusting to 40 to 70%. The final vacuum heat treatment step for improving the creep resistance is performed in the temperature range of 470 ° C. to 570 ° C. for 3 to 8 hours through the metal recrystallization degree monitoring so that the recrystallization degree is 40 to 70%. It is preferable to do so.

  The zirconium alloy composition of the present invention can improve the creep resistance by adjusting the recrystallization degree to 40 to 70%. Therefore, the zirconium alloy composition according to the present invention has excellent creep resistance. Thus, by minimizing creep deformation, safety and economy can be doubled compared to existing conventional materials. Therefore, the zirconium alloy composition according to the present invention can be usefully used as a nuclear fuel cladding tube, a supporting grid, and a structural material in the reactor cores of light water reactors and heavy water reactor type nuclear power plants. Further, by using the zirconium alloy composition according to the present invention as the material of the structure as described above, it is possible to ensure the soundness of the nuclear fuel rod in a high burnup / long cycle operation nuclear core.

Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are for illustrating the present invention, and the scope of the present invention is not limited or limited by the following examples.
Example

Examples 1 to 13: Production of Zirconium Alloy Four Example Alloys ((1) Zr-0.8% Nb-0.Nb) with Nb Content Changed from 0.8% to 1.8% 07% Cu-0.14% O-0.008% C-0.008% Si-0.002% S, (2) Zr-1.1% Nb-0.07% Cu-0.14% O -0.008% C-0.008% Si-0.002% S, (3) Zr-1.5% Nb-0.07% Cu-0.14% O-0.008% C-0. 008% Si-0.002% S, (4) Zr-1.8% Nb-0.07% Cu-0.14% O-0.008% C-0.008% Si-0.002% S );

Zr-1.5% Nb-0.4% Sn alloy ((5) Zr-1.5% Nb-0.4% Sn-0.14% O-0.008% C-0.008% Si- 0.002% S);

  Example alloy 4 types ((6) Zr-1.5% Nb-) in which one or more elements in Cu, Fe and Cr are added to the Zr-1.5% Nb-0.4% Sn alloy. 0.4% Sn-0.1% Cu-0.14% O-0.008% C-0.008% Si-0.002% S, (7) Zr-1.5% Nb-0.4 % Sn-0.1% Fe-0.14% O-0.008% C-0.008% Si-0.002% S, (8) Zr-1.5% Nb-0.4% Sn- 0.1% Cu-0.1% Fe-0.14% O-0.008% C-0.008% Si-0.002% S, (9) Zr-1.5% Nb-0.4 % Sn-0.2% Fe-0.1% Cr-0.14% O-0.008% C-0.008% Si-0.002% S);

  Example Alloys 4 in which the amount of sulfur added was changed from 0.0005% to 0.005% ((10) Zr-1.1% Nb-0.07% Cu-0.14% O-0.008 % C-0.008% Si-0.0005% S, (11) Zr-1.1% Nb-0.07% Cu-0.14% O-0.008% C-0.008% Si- 0.0010% S, (12) Zr-1.1% Nb-0.07% Cu-0.14% O-0.008% C-0.008% Si-0.0020% S, (13) Zr-1.1% Nb-0.07% Cu-0.14% O-0.008% C-0.008% Si-0.0050% S) The results are summarized in Table 1 (where “%” means “% by weight”).

  Forging was performed in a β region of 1000 to 1200 ° C. in order to melt the ingot by melting the zirconium alloy having the above composition and destroy the ingot structure in the ingot. Further, a solution heat treatment was performed at 1015 to 1075 ° C. to distribute the alloy elements more uniformly, and then rapidly cooled to obtain a β-rapidly cooled organization (martensite). The β-quenched material was hot-rolled at 590 ° C. with a reduction rate of 70%, subjected to primary cold working at a 50% reduction rate, and then subjected to vacuum heat treatment at 570 to 580 ° C. for 3 hours. The test piece subjected to the vacuum heat treatment was subjected to cold working three times, and the intermediate heat treatment between the cold work was performed in vacuum at 570 ° C. for 2 hours. Next, the final heat treatment was performed at 510 ° C. for 3 to 8 hours to produce a zirconium alloy sheet material specimen. Further, some examples of the alloys (Examples 2, 3, 7, 8, and 9) for evaluating the creep characteristics depending on the recrystallization degree were obtained by changing the final heat treatment temperature from 470 ° C. to 570 ° C. at intervals of 20 ° C. Morphological specimens were manufactured.

  In the present invention, the recrystallization degree is maintained within the range of 40 to 70% by appropriately adjusting the heat treatment temperature and time. The recrystallization degree was averaged by analyzing several (minimum 5 or more) base metal fine texture photographs taken using a transmission electron microscope with an image analyzer. The results are shown in FIG. FIG. 1 shows the change in recrystallization degree depending on the heat treatment temperature when the final heat treatment temperature is changed in the course of producing a zirconium alloy. When the heat treatment temperature was increased in the same time, the recrystallization degree tended to increase along the S curve.

Experimental Example 1: Chemical composition analysis Samples were sampled from 13 kinds of example alloys according to the present invention and the reference alloy Zircaloy-4, and their chemical compositions were analyzed. The results are shown in Table 2 below.

  As can be seen in Table 2, the analytical values agreed very well with the nominal values shown in Table 1. Accordingly, it can be seen that the alloy compositions of all the alloys for the examples are well controlled to meet the test purpose.

Experimental Example 2: Creep Test by Recrystallization Degree of Zirconium Alloy In order to examine the amount of creep deformation of the alloys manufactured according to Examples 2-3 and 7-9, a constant load of 120 MPa was applied to the test piece at 350 ° C. The creep test was conducted for 192 hours. The results are shown in FIG.

  The amount of creep deformation tended to decrease as the recrystallization degree increased, and all of the example alloys showed the minimum amount of creep deformation when the recrystallization degree was in the range of 40 to 70%. However, the amount of creep deformation tended to slightly increase when the recrystallization degree exceeded this range. The creep properties of the zirconium alloy have been shown to have a close relationship with the dislocation distribution present in the substrate structure. That is, the resistance to creep deformation was most excellent when the recrystallization degree progressed to an intermediate level (about 40 to 70%).

Experimental Example 3: Creep Test Depending on Alloy Element Content In order to investigate the recrystallization degree and the creep deformation rate of the 13 types of alloys manufactured in Examples 1 to 13, a constant load of 120 MPa was applied to the test piece at 350 ° C. In addition, the results of creep tests of 192 hours and 7200 hours are shown in Table 3 below.

  As can be seen from Table 3, the creep deformation rate of the alloys having compositions according to Examples 1 to 4 in which the Nb addition content was changed in the range of 0.8 to 1.8% by weight was measured under the two test conditions (192). The time was 0.22 to 0.31% and 0.48 to 0.62% in time (7200 hours), which was lower than the existing common material Zircaloy-4 (Zircaloy-4).

  Moreover, the Zr-1.5% Nb-0.4% Sn-based alloy having the composition according to Examples 5 to 9 showed more excellent creep resistance by the addition of Sn.

  In order to investigate the effect of sulfur addition on the creep characteristics, the amount of creep deformation of the alloys having the compositions according to Examples 10 to 13 of the present invention was observed. As can be seen from the results in Table 3 above, it is clearly shown that the amount of creep deformation decreases as the amount of sulfur added increases. If 0.002% by weight of sulfur is added, the amount of creep deformation does not decrease any more. It was. Sulfur added to improve creep resistance has been shown to be most effective in the range of 0.0006 to 0.0020% by weight.

  It can be seen that the recrystallization degrees of all 13 alloys of Examples 1 to 13 shown in Table 3 are in the range of 40 to 70%. It has been found that if the recrystallization degree is within this range, the creep resistance can be improved by 160% or more as compared with the existing Zircaloy-4.

  As seen in detail above, the zirconium alloy according to the present invention has excellent creep resistance by controlling the final heat treatment temperature and time so as to maintain the recrystallization degree at 40 to 70%. The creep resistance is superior to that of Zircaloy-4 which is an existing conventional nuclear fuel cladding tube material. In addition, the recrystallization degree presented in the present invention can be fully utilized for the production of a zirconium alloy having excellent creep characteristics, and can greatly contribute to the improvement of creep resistance.

  Therefore, the zirconium alloy according to the present invention can double safety and economy by minimizing creep deformation under high burnup / long cycle operating conditions, and can maintain soundness. It can be very useful for nuclear fuel cladding tubes, support grids and in-core structures, etc. in the reactor core of heavy water reactor nuclear power plant, and can replace Zircaloy-4 used in conventional nuclear fuel cladding material. it can.

3 is a graph showing the recrystallization degree of a zirconium alloy according to an embodiment of the present invention. 3 is a graph showing a creep deformation ratio according to a recrystallization degree of a zirconium alloy according to an embodiment of the present invention.

Claims (5)

  Niobium 0.8-1.8 wt%; Copper 0.05-0.15 wt%; Oxygen 0.10-0.15 wt%; Carbon 0.006-0.010 wt%; Silicon 0.006-0 A zirconium alloy composition comprising: 0.001 wt%; sulfur 0.0005-0.0020 wt%; and zirconium balance.   Niobium 0.8-1.8 wt%; Tin 0.38-0.50 wt%; Oxygen 0.10-0.15 wt%; Carbon 0.006-0.010 wt%; Silicon 0.006-0 A zirconium alloy composition comprising: 0.001 wt%; sulfur 0.0005-0.0020 wt%; and zirconium balance.   In addition to the above composition, one or more elements selected from 0.05 to 0.2% by weight of iron, 0.05 to 0.2% by weight of copper and 0.05 to 0.2% by weight of chromium The zirconium alloy composition according to claim 2, further comprising:   In addition to the above composition, the composition further comprises one or more elements selected from 0.1 to 0.2% by weight of iron, 0.05 to 0.15% by weight of copper and 0.12% by weight of chromium. The zirconium alloy composition according to claim 2, wherein: The zirconium alloy composition according to any one of claims 1 to 4, wherein a recrystallization degree of the zirconium alloy composition is adjusted to a range of 40 to 70%.

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