U.S. patent application number 11/734318 was filed with the patent office on 2008-06-05 for zirconium alloy composition having excellent corrosion resistance for nuclear applications and method of preparing the same.
This patent application is currently assigned to Korea Atomic Energy Research Institute. Invention is credited to Jong Hyuk Baek, Byoung Kwon Choi, Yong Hwan Jeong, Hyun Gil Kim, Jun Hwan Kim, Myung Ho Lee, Jeong Yong Park, Sang Yoon Park.
Application Number | 20080131306 11/734318 |
Document ID | / |
Family ID | 38171108 |
Filed Date | 2008-06-05 |
United States Patent
Application |
20080131306 |
Kind Code |
A1 |
Jeong; Yong Hwan ; et
al. |
June 5, 2008 |
ZIRCONIUM ALLOY COMPOSITION HAVING EXCELLENT CORROSION RESISTANCE
FOR NUCLEAR APPLICATIONS AND METHOD OF PREPARING THE SAME
Abstract
The present invention relates to a zirconium alloy composition
having excellent corrosion resistance for nuclear applications and
a method of preparing the same. The zirconium alloy composition
having excellent corrosion resistance for nuclear applications
includes 1.3.about.2.0 wt % of niobium, 0.05.about.0.18 wt % of
iron, 0.008.about.0.012 wt % of silicon, 0.008.about.0.012 wt % of
carbon, and 0.1.about.0.16 wt % of oxygen, with the balance being
zirconium, or includes 2.8.about.3.5 wt % of niobium, 0.2.about.0.7
wt % of at least one of iron and copper, 0.008.about.0.012 wt % of
silicon, 0.008.about.-0.012 wt % of carbon, and 0.1.about.0.16 wt %
of oxygen, with the balance being zirconium. The zirconium alloy
composition according to the present invention, in which the amount
of niobium, acting as a first alloying element, and the amount of
at least one of iron and copper, acting as a second alloying
element, are appropriately controlled, and silicon, carbon and
oxygen are added in appropriate amounts, can exhibit excellent
corrosion resistance, and thus can be usefully used as materials
for nuclear fuel cladding tubes, support ribs, and core components
of light water reactors and heavy water reactors.
Inventors: |
Jeong; Yong Hwan; (Daejeon,
KR) ; Baek; Jong Hyuk; (Daejeon, KR) ; Choi;
Byoung Kwon; (Daejeon, KR) ; Lee; Myung Ho;
(Daejeon, KR) ; Park; Sang Yoon; (Daejeon, KR)
; Park; Jeong Yong; (Daejeon, KR) ; Kim; Jun
Hwan; (Daejeon, KR) ; Kim; Hyun Gil; (Daejeon,
KR) |
Correspondence
Address: |
BACHMAN & LAPOINTE, P.C.
900 CHAPEL STREET, SUITE 1201
NEW HAVEN
CT
06510
US
|
Assignee: |
Korea Atomic Energy Research
Institute
Daejeon
KR
Korea Hydro and Nuclear Power Co., Ltd.
Seoul
KR
|
Family ID: |
38171108 |
Appl. No.: |
11/734318 |
Filed: |
April 12, 2007 |
Current U.S.
Class: |
420/423 ;
148/557; 420/422 |
Current CPC
Class: |
C22F 1/186 20130101;
Y02E 30/40 20130101; C22C 16/00 20130101; Y02E 30/30 20130101; G21C
3/07 20130101 |
Class at
Publication: |
420/423 ;
148/557; 420/422 |
International
Class: |
C22C 16/00 20060101
C22C016/00; C22F 1/16 20060101 C22F001/16 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 5, 2006 |
KR |
10-2006-0122414 |
Claims
1. A zirconium alloy composition having excellent corrosion
resistance for nuclear applications, comprising 1.3.about.2.0 wt %
of niobium, 0.05.about.0.18 wt % of iron, 0.008.about.0.012 wt % of
silicon, 0.008.about.0.012 wt % of carbon, and 0.1.about.0.16 wt %
of oxygen, with a balance being zirconium.
2. The zirconium alloy composition according to claim 1, wherein
said composition comprises 1.4.about.1.6 wt % of niobium,
0.08.about.0.12 wt % of iron, 0.009.about.0.011 wt % of silicon,
0.009.about.0.011 wt % of carbon, and 0.12.about.0.14 wt % of
oxygen, with the balance being zirconium.
3. A zirconium alloy composition having excellent corrosion
resistance for nuclear applications, comprising 2.8.about.3.5 wt %
of niobium, 0.2.about.0.7 wt % of at least one of iron and copper,
0.008.about.0.012 wt % of silicon, 0.008.about.0.012 wt % of
carbon, and 0.1.about.0.16 wt % of oxygen, with a balance being
zirconium.
4. The zirconium alloy composition according to claim 3, wherein
said composition comprises 2.8.about.3.2 wt % of niobium,
0.4.about.0.6 wt % of at least one of iron and copper,
0.009.about.0.011 wt % of silicon, 0.009.about.0.011 wt % of
carbon, and 0.12.about.0.14 wt % of oxygen, with the balance being
zirconium.
5. The zirconium alloy composition according to claim 3, wherein a
total amount of the iron and copper is 0.7 wt % or less.
6. A method of preparing a zirconium alloy composition according to
claim 1 to 5 comprising: a first step of mixing alloying elements
and then melting them, to thus prepare an ingot; a second step of
heat treating the ingot prepared in the first step in a
.beta.-region and then cooling it; a third step of hot rolling the
ingot heat treated and cooled in the second step; and a fourth step
of cold rolling and heat treating the ingot hot rolled in the third
step, thus preparing a zirconium alloy.
7. The method according to claim 6, which further comprises a final
heat treating following a further cold rolling after the heat
treating in the fourth step.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a zirconium alloy
composition having excellent corrosion resistance for nuclear
applications and to a method of preparing the same.
[0003] 2. Description of the Related Art
[0004] During the last several decades, zirconium alloys, which
have a small neutron absorption cross section and excellent
corrosion resistance and mechanical properties, have been widely
used as materials for nuclear fuel cladding tubes, nuclear fuel
assembly support grids, and structural components in pressurized
water reactors (PWRs) and boiling water reactors (BWRs). Among
zirconium alloys developed to date, particularly useful are
Zircaloy-2 (1.20.about.1.70 wt % of tin, 0.07.about.0.20 wt % of
iron, 0.05.about.1.15 wt % of chromium, 0.03.about.0.08 wt % of
nickel, 900.about.1500 ppm of oxygen, and the balance being
zirconium) and Zircaloy-4 (1.20.about.1.70 wt % of tin,
0.18.about.0.24 wt % of iron, 0.07.about.1.13 wt % of chromium,
900.about.1500 ppm of oxygen, less than 0.007 wt % of nickel, and
the balance of zirconium), comprising tin (Sn), iron (Fe), chromium
(Cr) and nickel (Ni).
[0005] However, in recent years, as part of the economic
improvement of nuclear reactors, in order to decrease nuclear fuel
cycle costs, high burn-up operation due to an extended refueling
cycle has been adopted. Accordingly, as the refueling cycle is
extended, the duration of reaction of the nuclear fuel with
high-temperature and high-pressure water and steam is increased.
Thus, in the case where conventional Zircaloy-2 or Zircaloy-4 is
used as material for nuclear fuel cladding tubes, problems in which
the nuclear fuel is severely corroded are on the rise.
[0006] Hence, there is an urgent need for the development of high
burn-up nuclear fuel cladding material having superior corrosion
resistance with respect to high-temperature and high-pressure water
and steam. A lot of research is being directed toward the
development of zirconium alloys having improved corrosion
resistance. As such, since the corrosion resistance of the
zirconium alloy is greatly affected by the types and amounts of
elements to be added, the working conditions, and heat treatment
conditions, establishing optimal conditions is the most important
factor for the induction of excellent corrosion resistance.
[0007] When briefly investigating patents concerning cladding tubes
of high burn-up and extended cycle nuclear fuel, registered after
the middle of the 1980s, the addition of niobium (Nb) and the
decrease in the amount of tin (Sn) are characteristic, compared to
the Zircaloy-based alloys. That is, the zirconium alloy for high
burn-up and extended cycle nuclear fuel essentially contains
niobium, and the optimal preparation process thereof is provided to
exhibit excellent performance. Further, for high creep resistance,
zirconium alloys, in which a small amount of sulfur (S) is added,
are registered, and high corrosion resistance accompanies the
control of amounts of alloying elements.
[0008] U.S. Pat. No. 4,649,023 discloses a zirconium alloy,
comprising 0.5.about.2.0 wt % of niobium, 0.9.about.1.5 wt % of
tin, 0.09.about.0.11 wt % of one element selected from the group
consisting of iron, chromium, molybdenum, vanadium, copper, nickel,
and tungsten, and 0.1.about.0.16 wt % of oxygen, with the balance
being zirconium, and also a process of preparing the alloy, in
which the size of the precipitate in a matrix is limited to 80 nm
or less.
[0009] U.S. Pat. No. 5,112,573, which specifies the alloy
composition disclosed in U.S. Pat. No. 4,649,023, discloses a
process of preparing a zirconium alloy, comprising 0.5.about.2.0 wt
% of niobium, 0.7.about.1.5 wt % of tin, 0.07.about.0.14 wt % of
iron, 0.03.about.0.14 wt % of nickel or chromium, and 0.022 wt % or
less of carbon, with the balance being zirconium.
[0010] U.S. Pat. Nos. 5,125,985 and 5,266,131 disclose a process of
preparing a zirconium alloy having the same composition as that
disclosed in U.S. Pat. No. 5,112,573, in which a .beta.-quenching
process is introduced at a late stage during cold-rolling of the
above alloy, in order to increase creep resistance and corrosion
resistance.
[0011] U.S. Pat. No. 5,648,995 discloses a method of preparing a
zirconium alloy comprising 0.8.about.1.3 wt % of niobium,
0.005.about.0.025 wt % of iron, 0.16 wt % or less of oxygen, 0.02
wt % or less of carbon, and 0.012 wt % or less of silicon, with the
balance being zirconium, in which the amount of iron is controlled
to be very low so as to increase creep resistance.
[0012] U.S. Pat. No. 5,832,050 discloses a method of adding
8.about.100 ppm of sulfur to eight various zirconium alloys,
including a zirconium alloy composed of 0.7.about.1.3 wt % of
niobium, 0.09.about.0.16 wt % of oxygen and the balance of
zirconium, in order to increase creep resistance, and a process of
preparing these alloys.
[0013] U.S. Pat. No. 6,544,361 discloses a zirconium alloy
comprising 0.8.about.1.3 wt % of niobium, 0.05.about.0.2 wt % of
oxygen, 300 ppm or less of tin, 0.25 wt % or less of
iron+chromium+vanadium, and 5.about.35 ppm of sulfur, and a process
of preparing material for a thin strap having excellent resistance
to creep, corrosion, and hydrogen absorption.
[0014] U.S. Pat. No. 5,940,464 discloses an alloy composition,
comprising 0.8.about.1.8 wt % of niobium, 0.2.about.0.6 wt % of
tin, 0.02.about.0.4 wt % of iron, 30.about.180 ppm of carbon,
10.about.120 ppm of silicon, and 600.about.1800 ppm of oxygen, with
the balance being zirconium, and a preparation process thereof, in
order to increase corrosion resistance and creep resistance.
[0015] U.S. Pat. Nos. 6,261,516, 6,514,360 and 6,902,634 disclose
various zirconium alloy compositions, including a zirconium alloy
composed of 1.1.about.1.7 wt % of niobium, 600.about.1600 ppm of
oxygen and 80.about.120 ppm of silicon, and a preparation process
thereof. As such, the preparation of the zirconium alloy, having
excellent corrosion resistance, requires that heat treatment
temperature and time, the precipitate size, and the concentration
of niobium oversaturated in a matrix be controlled.
[0016] In U.S. Pat. No. 4,938,920, the amount of tin is decreased
to 0.about.0.8 wt %, and 0.about.0.3 wt % of vanadium, 0.about.1.0
wt % of niobium, and 1000.about.1600 ppm of oxygen are added to
develop an alloy having higher corrosion resistance than that of
conventional Zircaloy-4. In this case, the amounts of iron and
chromium are set in the range of 0.2.about.0.8 wt % and 0.about.0.4
wt %, respectively, and the sum of iron, chromium and vanadium is
limited to 0.25.about.1.0 wt %.
[0017] U.S. Pat. No. 5,254,308 discloses a zirconium alloy
containing niobium and iron, which function to prevent the
deterioration of the mechanical properties of the alloy,
attributable to a decrease in the amount of tin, to improve the
corrosion resistance of the alloy. This alloy is composed of
0.45.about.0.75 wt % of tin, 0.4.about.0.53 wt % of iron,
0.2.about.0.3 wt % of chromium, 0.3.about.0.5 wt % of niobium,
0.012.about.0.3 wt % of nickel, 50.about.200 ppm of silicon, and
1000.about.2000 ppm of oxygen. The ratio of iron to chromium, which
may affect the corrosion properties, is fixed at 1.5, and the
amount of niobium is determined depending on the hydrogen
absorption. Furthermore, the amounts of nickel, silicon, carbon and
dissolved oxygen are finely controlled, resulting in excellent
corrosion resistance and strength.
[0018] U.S. Pat. No. 5,334,345 discloses an alloy composition,
comprising 1.0.about.2.0 wt % of tin, 0.07.about.0.7 wt % of iron,
0.05.about.0.15 wt % of chromium, 0.16.about.0.4 wt % of nickel,
0.015.about.0.3 wt % of niobium, 20.about.500 ppm of silicon and
900.about.1600 ppm of oxygen, in order to increase corrosion
resistance and hydrogen absorption.
[0019] U.S. Pat. No. 5,366,690 discloses an alloy composition, in
which the amounts of tin, nitrogen, and niobium are mainly
controlled, and which comprises 0.about.1.5 wt % of tin,
0.about.0.24 wt % of iron, 0.about.0.15 wt % of chromium,
0.about.2300 ppm of nitrogen, 0.about.100 ppm of silicon,
0.about.1600 ppm of oxygen, and 0.about.0.5 wt % of niobium.
[0020] U.S. Pat. No. 5,211,774 discloses a zirconium alloy
composition in order to increase the mechanical properties and
corrosion properties in a neutron irradiation environment. The
alloy is composed of 0.8.about.1.2 wt % of tin, 0.2.about.0.5 wt %
of iron, 0.1.about.0.4 wt % of chromium, 0.about.0.6 wt % of
niobium, 50.about.200 ppm of silicon, and 900.about.1800 ppm of
oxygen, in which the amount of silicon is varied in order to
decrease changes in hydrogen absorption and corrosion
resistance.
[0021] In the conventional techniques related to the zirconium
alloys mentioned above, Zircaloy-4 and various zirconium alloys
have been mainly developed, and furthermore, the zirconium alloys
containing niobium, iron, and chromium have also been developed in
order to increase corrosion resistance. However, compared to such
zirconium alloys, the development of zirconium alloys, having
superior corrosion resistance suitable for high burn-up and
extended fuel cycle operating conditions in nuclear power plants,
is still required.
SUMMARY OF THE INVENTION
[0022] Leading to the present invention, thorough research into
zirconium alloys having high corrosion resistance, carried out by
the present inventors aiming to solve the problems encountered in
the prior art, resulted in the development of a zirconium alloy
composition having excellent corrosion resistance by controlling
the amounts of alloying elements, including niobium, iron, copper,
silicon, carbon, and oxygen.
[0023] An object of the present invention is to provide a zirconium
alloy composition having excellent corrosion resistance, which can
be used as material for nuclear fuel cladding tubes and core
components under high temperature/high pressure conditions of light
water reactors and heavy water reactors.
[0024] In order to accomplish the above object, the present
invention provides a zirconium alloy composition having excellent
corrosion resistance, comprising 1.3.about.2.0 wt % of niobium,
0.05.about.0.18 wt % of iron, 0.008.about.0.012 wt % of silicon,
and 0.1.about.0.16 wt % of oxygen, with the balance being
zirconium.
[0025] In addition, the present invention provides a zirconium
alloy composition having excellent corrosion resistance, comprising
2.8.about.3.5 wt % of niobium, 0.2.about.0.7 wt % of at least one
of iron and copper, 0.008.about.0.012 wt % of silicon,
0.008.about.0.012 wt % of carbon, and 0.1.about.0.16 wt % of
oxygen, with the balance being zirconium.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a graph showing the corrosion properties of the
zirconium alloy with respect to water (O) and steam (.quadrature.)
depending on the amount of iron in the
Zr--1.5Nb--xFe--0.01Si-0.01C--0.13O alloy; and
[0027] FIG. 2 is a graph showing the corrosion properties of the
zirconium alloy with respect to water (O) and steam (.quadrature.)
depending on the total amount of iron and copper in the
Zr--3.0Nb--x(Fe+Cu)--0.01Si--0.01C--0.13O alloy.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Hereinafter, a detailed description will be given of the
present invention.
[0029] According to the present invention, the zirconium alloy
composition comprises 1.3.about.2.0 wt % of niobium,
0.05.about.0.18 wt % of iron, 0.008.about.0.012 wt % of silicon,
and 0.1.about.0.16 wt % of oxygen, with the balance being
zirconium, and preferably comprises 1.4.about.1.6 wt % of niobium,
0.08.about.0.12 wt % of iron, 0.009.about.0.011 wt % of silicon,
0.009.about.0.011 wt % of carbon, and 0.12.about.0.14 wt % of
oxygen, with the balance being zirconium.
[0030] In addition, the zirconium alloy composition according to
the present invention comprises 2.8.about.3.5 wt % of niobium,
0.2.about.0.7 wt % of at least one of iron and copper,
0.008.about.0.012 wt % of silicon, 0.008.about.0.012 wt % of
carbon, and 0.1.about.0.16 wt % of oxygen, with the balance being
zirconium, and preferably comprises 2.8.about.3.2 wt % of niobium,
0.4.about.0.6 wt % of at least one of iron and copper,
0.009.about.0.011 wt % of silicon, 0.009.about.0.011 wt % of
carbon, and 0.12.about.0.14 wt % of oxygen, with the balance being
zirconium.
[0031] The most important problem to be solved for nuclear fuel
used in high burn-up and extended cycle conditions is the drastic
increase in surface corrosion due to high heat flux and long
exposure time under reactor conditions. When the corrosion is
increased, an oxide film, which is highly brittle, is increasingly
formed, and furthermore, hydrogen is introduced in a large amount
into a matrix, undesirably deteriorating the structural soundness
of nuclear fuel rods. Thus, the development of material for
cladding tubes having excellent corrosion resistance can directly
contribute to the increase in economic efficiency of light water
reactors and heavy water reactors and the improvement of safety
thereof. In the present invention, with the goal of inhibiting the
corrosion under reactor conditions, niobium, which is known to
greatly contribute to an increase in corrosion resistance in a
neutron irradiation environment, is added in as large an amount as
possible. Further, iron and copper are added in appropriate
amounts, thus increasing corrosion resistance.
[0032] Below, individual elements of the zirconium alloy
composition of the present invention are specifically
described.
[0033] (1) Niobium (1.sup.st Alloying Element)
[0034] Niobium is known as a .beta.-phase stabilizer element of
zirconium. The influence of niobium on corrosion resistance is
variable. Typically, when niobium is added in an amount of 0.5 wt %
or less (low niobium content) or 1.0 wt % or more (high niobium
content), corrosion resistance is known to be improved.
[0035] When niobium is added to a zirconium matrix in an amount not
less than a solid solubility thereof, the zirconium matrix is
hardened due to the solid solution of niobium and precipitation of
niobium, thus improving the mechanical properties of zirconium.
[0036] The niobium, which is added to the zirconium alloy,
essentially functions to increase corrosion resistance and also
affects an increase of tensile and creep performance. The amount of
niobium used in the present invention may be adjusted depending on
the amount of at least one of iron and copper. In the case where
iron, acting as a second alloying element, is used in an amount
less than 0.2 wt %, niobium is preferably added in an amount of
1.3.about.2.0 wt %. On the other hand, in the case where at least
one of iron and copper is added in an amount not less than 0.2 wt
%, niobium is preferably added in an amount of 2.8.about.3.5 wt %.
If the amount thereof falls outside of the above range, the
corrosion resistance of the zirconium alloy is decreased.
[0037] (2) Iron and Copper (2.sup.nd Alloying Elements)
[0038] Iron and copper, which are added as second alloying
elements, are known to increase the corrosion resistance of the
zirconium alloy. Even when they are added in very small amounts,
corrosion resistance is increased. In the zirconium alloy
composition according to the present invention, when iron is added
in an amount less than 0.2 wt %, the amount thereof is preferably
controlled in the range of 0.05.about.0.18 wt %. On the other hand,
in the case where iron and copper is added in an amount not less
than 0.2 wt %, the amount thereof is preferably adjusted in the
range of 0.2.about.0.7 wt %. If the amount thereof falls outside of
the above range, the corrosion resistance of the zirconium alloy is
decreased.
[0039] In the zirconium alloy composition of the present invention,
the amount of niobium is increased in proportion to an increase in
amount of at least one of iron and copper. However, when the total
amount of iron and copper added exceeds 0.7 wt %, defects in the
working zone may occur. Consequently, it is preferred that the
total amount of iron and copper be not more than 0.7 wt %.
[0040] (3) Silicon, Carbon, and Oxygen
[0041] Silicon and carbon function to decrease hydrogen absorption
in the zirconium matrix and to retard a transition phenomenon,
causing a drastic increase in corrosion over time, and oxygen is
dissolved in the zirconium matrix to generate a solid solution so
as to increase the mechanical strength of the zirconium alloy.
[0042] In the zirconium alloy composition of the present invention,
silicon and carbon, which are used in a very small amount, are
preferably added in an amount of 0.008.about.0.012 wt %, and oxygen
is preferably added in an amount of 0.1.about.0.16 wt %. If the
amount of silicon and carbon falls outside of the above range,
corrosion resistance is decreased, and furthermore, if the amount
of oxygen falls outside of the above range, low corrosion
resistance and poor workability may result.
[0043] The zirconium alloy composition of the present invention may
be prepared using a typical process known in the art, and the
preparation method thereof preferably comprises a first step of
mixing and melting alloying elements to thus prepare an ingot, a
second step of heat treating the ingot prepared in the first step
in a .beta.-region and cooling it, a third step of subjecting the
ingot heat treated and cooled in the second step to hot rolling,
and a fourth step of subjecting the ingot treated in the third step
to cold rolling and heat treating, thus preparing a zirconium
alloy. After the cold rolling of the fourth step, final heat
treatment may be further included.
[0044] Below, the preparation method of the present invention is
stepwisely described in detail.
[0045] The first step is a process of mixing the alloying elements
at a predetermined ratio and melting them, thus preparing the
ingot.
[0046] The ingot is preferably prepared using a vacuum arc
remelting (VAR) process. Specifically, the vacuum state in a
chamber is maintained at 1.times.10.sup.-5 torr, after which argon
(Ar) gas is injected thereto at 0.1.about.0.3 torr and
500.about.1000 A of current is applied, to thus perform the melting
process, and then a cooling process is conducted, thereby preparing
the ingot in the shape of a button.
[0047] As such, in order to prevent the segregation of impurities
or the non-uniform distribution of the alloy composition in the
button, it is preferred that the melting process be repeated three
to six times. In the cooling process, in order to prevent the
surface of the test piece from being oxidized, inert gas, such as
argon, is preferably injected.
[0048] Subsequently, the second step is a process of heat treating
the ingot, prepared in the first step, in a .beta.-region and then
cooling it.
[0049] To homogenize the alloy composition in the ingot and obtain
fine precipitates, the ingot is heat treated in a .beta.-region and
then cooled. As such, with the goal of preventing the test piece
from being oxidized, the test piece is clad with stainless steel,
and heated treated at 1000.about.1200.degree. C., and preferably at
1020.about.1070.degree. C., for 5-30 min, and preferably for 10-20
min. After the heat treatment, a quenching process using water at
room temperature is preferably performed.
[0050] Subsequently, the third step is a process of hot rolling the
test piece treated in the second step. Specifically, the hot
rolling process is performed in a manner such that the test piece
is preheated to 550.about.750.degree. C., and preferably to
580.about.610.degree. C., for 2.about.50 min, and preferably for
5.about.40 min, and is rolled at a reduction ratio of 40.about.80%,
and preferably 50.about.70%.
[0051] After the hot rolling process is performed, the cladding is
removed, and then an oxide film which is generated upon .beta.-heat
treatment or hot rolling, is removed using an acid solution.
Furthermore, portions of the oxide film, remaining after the acid
cleaning process, may be completely removed through a mechanical
process using an electromotive wire brush.
[0052] Subsequently, the fourth step is a process of cold rolling
and heat treating the test piece which was hot rolled in the third
step, thus preparing the zirconium alloy.
[0053] The hot rolled test piece is subjected to annealing at
550.about.610.degree. C., and preferably at 560.about.600.degree.
C., for a time period from 20 min to 3 hours, and then to cold
rolling at a reduction ratio of 40.about.60%, after which heat
treatment at 560.about.600.degree. C. for 1.about.3 hours and cold
rolling are repeated. In this case, the heat treatment and cold
rolling are repeated several times, and preferably, three to five
times.
[0054] After the final cold rolling process is performed, final
heat treatment for recrystallization or relieving residual stress
may be further included. This final heat treatment is preferably
performed at 500.about.600.degree. C. for 1.about.3 hours.
According to this method, the zirconium alloy composition according
to the present invention can be prepared.
[0055] As the results of a corrosion test, the zirconium alloy
composition of the present invention, comprising the above elements
and amounts, can be seen to exhibit excellent corrosion resistance
(Table 2), and therefore can be usefully used in high burn-up
nuclear fuel cladding tubes, support ribs, and structural
components of nuclear power plants.
[0056] A better understanding of the present invention may be
obtained through the following examples, which are set forth to
illustrate, but are not to be construed as the limit of the present
invention.
EXAMPLE 1
Preparation of Zirconium Alloy
[0057] (1) Preparation of Ingot
[0058] A zirconium alloy composition, comprising 1.58 wt % of
niobium, 0.05 wt % of iron, 0.01 wt % of silicon, 0.01 wt % of
carbon, and 0.13 wt % of oxygen, with the balance being zirconium,
was subjected to VAR to thus prepare an ingot having a weight of
200 g in a button shape. As such, as zirconium, reactor grade
sponge zirconium, described in ASTM B349, was used, and the
alloying elements had high purity of 99.99% or more. In addition,
silicon, carbon, and oxygen were subjected along with sponge
zirconium to first melting to thus prepare a mother alloy, which
was then added in a desired amount upon ingot melting. In order to
prevent the segregation of impurities or the non-uniform
distribution of the alloy composition, the melting process was
repeated four times. Further, in order to prevent the oxidation
upon the melting process, the vacuum state in a chamber was
maintained at 1.times.10.sup.-5 torr, argon gas having high purity
of 99.99% was injected, and 500 A of current was applied, and thus
an ingot was prepared in a water-cooled copper crucible having a
diameter of 60 mm at a water pressure of 1 kgf/cm.sup.2.
[0059] (2) .beta.-Heat Treatment
[0060] To uniformly distribute the alloy composition in the ingot,
the prepared ingot was subjected to solution heat treatment at
1050.degree. C., which was a .beta.-phase temperature, for 15 min.
To prevent the test piece from being oxidized, the test piece was
clad with a stainless steel plate 1 mm thick. After the completion
of the heat treatment, the ingot was dropped into a water bath
filled with water at room temperature to thus be quenched,
resulting in a martensite structure. Thereafter, the ingot was
dried at 150.degree. C. for 24 hours to remove water from the
cladding thereof.
[0061] (3) Hot Rolling
[0062] A hot rolling process was performed using a rolling mill
having a capacity of 100 tons. The test piece was preheated to
590.degree. C. for 30 min and then rolled at a reduction ratio of
about 70% per pass. After the hot rolling process, the cladding was
removed, and an oxide film, resulting from .beta.-heat treatment or
hot rolling, was removed using an acid solution comprising
hydrofluoric acid:nitric acid:water=5%:45%:50% at a volume ratio.
Subsequently, portions of the oxide film remaining after the acid
cleaning were completely removed using an electromotive wire
brush.
[0063] (4) Cold Rolling and Heat Treatment
[0064] In order to remove residual stress after the hot rolling
process and to prevent the test piece from breaking down when first
cold rolled, the test piece was annealed at 590.degree. C. for 30
min, and was then subjected to first cold rolling at a reduction
ratio of 50% according to a decrease in thickness of about 0.5 mm
per pass using a rolling mill having a capacity of 70 tons.
Thereafter, the first cold rolled test piece was subjected to
intermediate recrystallization heat treatment at 570.degree. C. for
2.5 hours, and then to second cold rolling at a reduction ratio of
50%. Thereafter, the second cold rolled test piece was subjected to
intermediate recrystallization heat treatment at 570.degree. C. for
2.5 hours and then to third cold rolling at a reduction ratio of
50%.
[0065] (5) Final Heat Treatment
[0066] The test piece was subjected to final heat treatment at
510.degree. C. for 2.5 hours to relieve the stress generated after
the cold rolling process. The test piece, which was subjected to
final heat treatment, was about 0.7 mm thick.
EXAMPLE 2
[0067] The present example was performed in the same manner as in
Example 1, with the exception that a zirconium alloy composition,
comprising 1.51 wt % of niobium, 0.09 wt % of iron, 0.01 wt % of
silicon, 0.01 wt % of carbon, and 0.13 wt % of oxygen, with the
balance being zirconium, was used.
EXAMPLE 3
[0068] The present example was performed in the same manner as in
Example 1, with the exception that a zirconium alloy composition,
comprising 1.72 wt % of niobium, 0.14 wt % of iron, 0.01 wt % of
silicon, 0.01 wt % of carbon, and 0.13 wt % of oxygen, with the
balance being zirconium, was used.
EXAMPLE 4
[0069] The present example was performed in the same manner as in
Example 1, with the exception that a zirconium alloy composition,
comprising 1.38 wt % of niobium, 0.18 wt % of iron, 0.01 wt % of
silicon, 0.01 wt % of carbon, and 0.13 wt % of oxygen, with the
balance being zirconium, was used.
EXAMPLE 5
[0070] The present example was performed in the same manner as in
Example 1, with the exception that a zirconium alloy composition,
comprising 3.01 wt % of niobium, 0.21 wt % of iron, 0.01 wt % of
silicon, 0.01 wt % of carbon, and 0.13 wt % of oxygen, with the
balance being zirconium, was used, and final heat treatment was
conducted at 570.degree. C.
EXAMPLE 6
[0071] The present example was performed in the same manner as in
Example 5, with the exception that a zirconium alloy composition,
comprising 3.12 wt % of niobium, 0.48 wt % of iron, 0.01 wt % of
silicon, 0.01 wt % of carbon, and 0.13 wt % of oxygen, with the
balance being zirconium, was used.
EXAMPLE 7
[0072] The present example was performed in the same manner as in
Example 5, with the exception that a zirconium alloy composition,
comprising 3.05 wt % of niobium, 0.24 wt % of copper, 0.01 wt % of
silicon, 0.01 wt % of carbon, and 0.13 wt % of oxygen, with the
balance being zirconium, was used.
EXAMPLE 8
[0073] The present example was performed in the same manner as in
Example 5, with the exception that a zirconium alloy composition,
comprising 2.95 wt % of niobium, 0.51 wt % of copper, 0.01 wt % of
silicon, 0.01 wt % of carbon, and 0.13 wt % of oxygen, with the
balance being zirconium, was used.
EXAMPLE 9
[0074] The present example was performed in the same manner as in
Example 5, with the exception that a zirconium alloy composition,
comprising 3.09 wt % of niobium, 0.05 wt % of iron, 0.25 wt % of
copper, 0.01 wt % of silicon, 0.01 wt % of carbon, and 0.13 wt % of
oxygen, with the balance being zirconium, was used.
EXAMPLE 10
[0075] The present example was performed in the same manner as in
Example 5, with the exception that a zirconium alloy composition,
comprising 3.11 wt % of niobium, 0.27 wt % of iron, 0.28 wt % of
copper, 0.01 wt % of silicon, 0.01 wt % of carbon, and 0.13 wt % of
oxygen, with the balance being zirconium, was used.
EXAMPLE 11
[0076] The present example was performed in the same manner as in
Example 5, with the exception that a zirconium alloy composition,
comprising 2.98 wt % of niobium, 0.32 wt % of iron, 0.35 wt % of
copper, 0.01 wt % of silicon, 0.01 wt % of carbon, and 0.13 wt % of
oxygen, with the balance being zirconium, was used.
COMPARATIVE EXAMPLE 1
[0077] The present example was performed in the same manner as in
Example 1, with the exception that a zirconium alloy composition,
comprising 1.55 wt % of niobium, 0.01 wt % of silicon, 0.01 wt % of
carbon, and 0.13 wt % of oxygen, with the balance being zirconium,
was used without the addition of copper or iron.
COMPARATIVE EXAMPLE 2
[0078] The present example was performed in the same manner as in
Example 1, with the exception that a zirconium alloy composition,
comprising 3.1 wt % of niobium, 0.01 wt % of silicon, 0.01 wt % of
carbon, and 0.13 wt % of oxygen, with the balance being zirconium,
was used without the addition of copper or iron.
COMPARATIVE EXAMPLE 3
[0079] A reactor grade Zircaloy-4, which was commercially available
as material for nuclear fuel cladding tubes of nuclear power
plants, was used.
[0080] The zirconium alloy compositions are shown in Table 1
below.
TABLE-US-00001 TABLE 1 Ratio of Zirconium Alloy Composition No.
Nb(wt %) Fe(wt %) Cu(wt %) C(wt %) O(wt %) Si(wt %) Zr Ex. 1 1.58
0.05 0.01 0.13 0.01 Balance Ex. 2 1.51 0.09 0.01 0.13 0.01 Balance
Ex. 3 1.72 0.14 0.01 0.13 0.01 Balance Ex. 4 1.38 0.18 0.01 0.13
0.01 Balance Ex. 5 3.01 0.21 0.01 0.13 0.01 Balance Ex. 6 3.12 0.48
0.01 0.13 0.01 Balance Ex. 7 3.05 0.24 0.01 0.13 0.01 Balance Ex. 8
2.95 0.51 0.01 0.13 0.01 Balance Ex. 9 3.09 0.05 0.25 0.01 0.13
0.01 Balance Ex. 10 3.11 0.27 0.28 0.01 0.13 0.01 Balance Ex. 11
2.98 0.32 0.35 0.01 0.13 0.01 Balance C. Ex. 1 1.55 0.01 0.13 0.01
Balance C. Ex. 2 3.10 0.01 0.13 0.01 Balance C. Ex. 3 Sn: 1.35 wt
%, Fe: 0.2 wt %, Cr: 0.1 wt %, O: 0.12 wt %, (Zircaloy- Zr: balance
4)
EXPERIMENTAL EXAMPLE 1
Corrosion Test
[0081] In order to evaluate the corrosion resistance of the
zirconium alloy composition according to the present invention, the
following corrosion test was conducted.
[0082] Each of the zirconium alloys of Examples 1.about.11 and
Comparative Examples 1.about.3 was formed into a corrosion test
piece in the shape of a coupon having a size of 15 mm.times.25
mm.times.0.7 mm, after which the surface thereof was polished using
SiC polishing paper of 800 grit. Thereafter, the test piece was
dipped into a solution of water:nitric acid:hydrofluoric acid at a
volume ratio of 50:45:5, to thus remove impurities and fine defects
from the surface thereof. The alloy test piece thus surface treated
was measured for surface area and initial weight immediately before
it was loaded into an autoclave. Thereafter, the test piece was
loaded into the autoclave, having water at 360.degree. C. (18.5
MPa) and a steam atmosphere at 400.degree. C. (10.3 MPa) to thus
undergo corrosion for 546 days, after which the weight of the test
piece was measured. The extent of corrosion was calculated using
the weight increase per surface area, and thus qualitatively
evaluated. The results of the corrosion test are shown in Table 2
below.
TABLE-US-00002 TABLE 2 Weight Increase (mg/dm.sup.2) No. Water at
360.degree. C. Steam at 400.degree. C. Ex. 1 64 198 Ex. 2 56 187
Ex. 3 52 165 Ex. 4 51 159 Ex. 5 68 209 Ex. 6 61 192 Ex. 7 67 193
Ex. 8 65 178 Ex. 9 63 196 Ex. 10 61 198 Ex. 11 58 202 C. Ex. 1 73
223 C. Ex. 2 77 251 C. Ex. 3 172 252
[0083] As is apparent from Table 2, in the zirconium alloys of
Examples 1.about.11 comprising the zirconium alloy composition of
the present invention, the weight increases attributable to
corrosion by water were determined to be 51.about.65 mg/dm.sup.2,
which were lower than those of the comparative examples (73, 77 or
172 mg/dm.sup.2), resulting in superior corrosion resistance.
Furthermore, even in the case of corrosion by steam, the weight
increases were determined to be 159-209 mg/dm.sup.2, which were
lower than those of the comparative examples (223, 251 or 252
mg/dm.sup.2), leading to excellent corrosion resistance.
Accordingly, the zirconium alloy composition of the invention has
excellent corrosion resistance with respect to water and steam, and
therefore can be usefully used in high burn-up nuclear fuel
cladding tubes, support ribs, and reactor structural components of
nuclear power plants.
EXPERIMENTAL EXAMPLE 2
Corrosion Test Depending on Amount of Iron or Copper
[0084] The zirconium alloy of the invention was subjected to the
following test to evaluate the corrosion resistance thereof
depending on the amount of iron or copper.
[0085] (1) Corrosion Resistance Depending on Amount of Iron
[0086] While the amount of iron was increased in the alloy
compositions of Examples 1.about.4 and Comparative Example 1
(Zr--1.5Nb--xFe--0.01Si--0.01C--0.13O alloy), corrosion resistance
was qualitatively evaluated in the same manner as in Test Example
1. The results are shown in FIG. 1.
[0087] As illustrated in FIG. 1, as the amount of iron was
increased in the zirconium alloy, the weight increase of the test
piece was seen to be decreased. That the weight increase was
decreased indicated less adsorption of impurities, thus resulting
in low corrosion. Therefore, when the amount of iron was increased
in the zirconium alloy, corrosion resistance was observed to
increase.
[0088] (2) Corrosion Resistance Depending on Total Amounts of Iron
and Copper
[0089] While the total amounts of iron and copper (Fe+Cu) was
increased in the alloy compositions of Examples 5.about.11 and
Comparative Example 2 (Zr--3.0Nb--x(Fe+Cu)--0.01Si--0.01C--0.13O
alloy), corrosion resistance was qualitatively evaluated using the
same manner as in Test Example 1. The results are shown in FIG.
2.
[0090] As illustrated in FIG. 2, as the total amounts of iron and
copper were increased in the zirconium alloy, the weight increase
of the test piece was decreased, leading to high corrosion
resistance.
[0091] As described hereinbefore, the present invention provides a
zirconium alloy composition having excellent corrosion resistance
for nuclear applications and a method of preparing the same. In the
zirconium alloy composition according to the invention, the amount
of niobium, acting as a first alloying element, and the amount of
at least one of iron and copper, acting as a second alloying
element, are appropriately controlled, and silicon, carbon and
oxygen are added in appropriate amounts, therefore realizing
excellent corrosion resistance. Thus, the zirconium alloy
composition of the invention can be usefully used as materials for
nuclear fuel cladding tubes, support ribs, and core components of
light water reactors and heavy water reactors.
[0092] Although the preferred embodiments of the present invention
have been disclosed for illustrative purposes, those skilled in the
art will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
* * * * *