JP2001004769A - High-corrosion-resistance zirconium alloy for nuclear reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the use of an alloy whose corrosion resistance is bad and from which an oxide film is exfoliated by a method wherein the corrosion resistance of the alloy is judged by using a correlation between a solid solubility constant as a characteristic by which the component of a precipitate is eluted due to irradiation and the corrosion resistance of the alloy. SOLUTION: The corrosion resistance of this zirconium alloy for a nuclear reactor is judged, e.g. in the production process of a fuel cladding tube. First, a sample for an electron microscope is prepared from a remainder material or the like generated in a final process for the manufacture of the cladding tube, and the average composition and the average particle size of an iron-chromium-based precipitate and an iron-nickel-based precipitate are found. The average composition, the average particle side and a weighed and mixed chemical composition are substituted into a prescribed numerical formula. A solid solubility constant as a material-inherent constant which expresses the concentration or iron and nickel in a base material which is increased when the iron and the nickel in the precipitate are eluted due to fast neutrons at a unit dose from the alloy is at a prescribed value or higher is judged, and the corrosion resistance of a product is evaluated. When the solid solubility constant becomes larger than a certain value, the corrosion susceptibility of the alloy becomes very small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high corrosion resistant zirconium alloy for a nuclear reactor, and more particularly to a zirconium alloy consisting essentially of iron, chromium, nickel and zirconium, or a zirconium alloy consisting essentially of iron, chromium, nickel, tin and zirconium. To a zirconium alloy.

[0002]

2. Description of the Related Art In order to efficiently react thermal neutrons and uranium required for fission reactions with fuel cladding tubes and fuel members,
Zirconium with a small thermal neutron absorption cross section is selected,
In consideration of corrosion resistance and strength, a zircon alloy and a zirconium-niobium alloy have been developed. Among them, alloys widely used as fuel cladding tubes and core structural materials in boiling water light water reactors, pressurized water light water reactors, etc.
And Jill force opening a-4. Table 1 shows the alloy compositions of Jirokuto A-2 and Jirokuto A-4 specified in JIS H4751.

[0003]

[Table 1]

When these zirconium alloys are used in a boiling water type light water reactor, there has been a problem that lens-shaped local corrosion called nodular corrosion occurs during operation of the reactor. However, when the zirconium alloy is converted to α + β phase or β
With the introduction of a heat treatment method of short-time heating to the temperature range of the phase and then quenching, and the change of the alloy composition, the occurrence of nodular corrosion is suppressed in the current specification zirconium alloy, and the corrosion is becoming uniform.

[0005] However, even when a zirconium alloy is manufactured with an alloy composition that suppresses nodular corrosion, the corrosion behavior varies depending on the manufacturing conditions, and an oxide film may grow thick. Thick oxide film may peel off,
If this floats on the reactor water, the radioactivity concentration of the reactor water is increased, and there is a possibility that the worker's exposure dose will increase during periodic inspections.

[0006]

Even when a zirconium alloy is manufactured with an alloy composition that suppresses nodular corrosion, the corrosion behavior varies depending on the manufacturing conditions, and an oxide film may grow thick. This is because the corrosion behavior of zirconium alloys is affected not only by the alloy composition, but also by the size and composition of intermetallic compounds that precipitate in the alloy. Was needed.

The present invention has been made in view of the above, and an object of the present invention is to provide a zirconium alloy having excellent corrosion resistance. In other words, the present invention sorts out these effects by increasing the iron and nickel concentrations in the base metal due to the dissolution of iron and nickel from the intermetallic compound into the base material per unit dose of fast neutrons. The corrosion resistance of the zirconium alloy is determined using the strong correlation of The present invention can prevent the use of a zirconium alloy having low corrosion resistance and the risk of oxide film peeling in a nuclear reactor, so that the radioactivity concentration in the reactor water is kept low and the exposure of workers during periodic inspections is reduced. Can be suppressed.

[0008]

Means for Solving the Problems Fuels for boiling water reactors are mainly composed of 0.07 to 0.20% by weight of iron, 0.0% to 0.20%.
A zirco-2 is used which consists of 5 to 0.15% chromium, 0.03 to 0.08% nickel, 1.20 to 1.70% tin and the balance substantially zirconium. .

According to recent studies, the corrosion behavior of fuel cladding for boiling water reactors does not depend on the uniform corrosion or nodular corrosion, and the intermetallic compounds, iron and nickel, which precipitate in the alloy, form fast neutrons. It was found that there is a strong correlation between the iron + nickel concentration in the base material, which increases per unit time due to melting out by irradiation, and the amount of corrosion (see * 1 on the following page).

FIG. 2 shows how iron and nickel, which are intermetallic compounds precipitated in the Jirikiguchi A-2, are melted out by irradiation with fast neutrons. The intermetallic compound substantially composed of iron, nickel, and zirconium and the intermetallic compound composed of iron, chromium, and zirconium are deposited in the zirikiguchi a-2.

Hereinafter, these are referred to as an iron / nickel-based precipitate and an iron / chromium-based precipitate, respectively. From the iron / nickel-based precipitate, iron and nickel dissolve into the base material at almost the same rate, and from the iron / chromium-based precipitate, iron preferentially dissolves into the base material. Such a phenomenon that the components of the precipitates dissolve into the base material by irradiation is called irradiation-induced solid solution, and it is known that the smaller the precipitates and the larger the fast neutron flux, the more easily they occur.

FIG. 3 shows the correlation between the maximum oxide film thickness of the fuel stack portion of the fuel cladding tube and the solid solution constant. The solid solution constant is a material-specific constant representing the iron and nickel concentration of the base metal increased by the fact that iron and nickel of the precipitates are melted out by high-speed neutron irradiation of the alloy at a unit irradiation dose (1 n / m ² ). . The maximum oxide film thickness used here is a measured value obtained by observing the gold phase of a Zircaloy-2 fuel cladding tube having a different particle size and composition of the precipitate, the composition of the alloy, the manufacturing capability, and the corrosion environment, The solid solution constant is a calculated value obtained by using an equation based on the analysis results of the iron, nickel and chromium concentrations of the base material and the precipitate. From this result, it can be seen that the smaller the solid solution constant, the more the maximum oxide film thickness varies, and the greater the corrosion sensitivity due to the environment.

The larger the solid solution constant is, the smaller the variation of the maximum oxide film is, and it is about 1.2 × 10 to ²⁶ (at% /
Above (n / m ² )), it can be seen that the corrosion sensitivity is very small. The corrosion resistance of a zirconium alloy used in a nuclear reactor is determined by utilizing the property of low corrosion sensitivity of a zirconium alloy having a solid solution constant of 1.2 × 10 to ²⁶ (at% / (n / m ² )) or more. be able to.

The following two methods can be considered to determine the solid solution constant. One is a method of formulating an empirical formula of the iron and nickel concentrations in the base material, the alloy composition, the precipitate particle size, the precipitate composition, and the fast neutron irradiation amount, and then calculating the solid solution constant. A number of zirconium alloys with different alloy composition, precipitate particle size, and precipitate composition are irradiated in a nuclear reactor to analyze the elemental concentration of the base metal, and an empirical formula is created from the analysis results and the calculation results of the fast neutron irradiation amount using a calculation code. From this empirical formula, the solid solution constant representing the increased elemental concentration of the base metal that has been melted out of the intermetallic compound precipitated in the alloy by receiving a unit dose of fast neutrons can be determined.

Another is the theory of pop-out damage (see the following page *
2) based on a theoretical formula created based on this.
First, the manner in which iron and nickel on the surface of the precipitate are transferred by fast neutrons is theoretically expressed as a mathematical formula, and the number of iron and nickel dissolved in the base material from one iron / nickel-based precipitate and the amount of iron / chromium The relational expression between the number of iron dissolved from the system precipitate and the fast neutron irradiation dose is created. Next, the analysis of iron and nickel concentrations in the base metal of the alloy actually irradiated in the reactor,
The coefficients in the formula are obtained using the results of the composition analysis of the precipitates, the particle size measurement, and the calculation results of the fast neutron irradiation dose by the code. The fact that iron and nickel are hardly dissolved in the base material of the alloy before measurement and irradiation, the composition analysis of precipitates before irradiation, particle size measurement, and the intermetallic precipitation per unit volume of zirconium alloy from alloy components Determine the number of compounds, and from the relational expression between the number of iron and nickel dissolved and the amount of fast neutron irradiation, increase the concentration of iron and nickel in the base metal due to the dissolution of iron and nickel precipitates by fast neutron irradiation. And the relational expression of fast neutron dose is obtained. Further, if it is differentiated by the fast neutron irradiation dose, an equation representing the solid solution constant is obtained.

The solid solution constant used in FIG. 3 is the solid solution constant at the start of irradiation determined by the latter method.

[0017]

(Equation 23)

[0018] Iron, nickel,
Since chromium hardly forms a solid solution, it is assumed that all precipitate as intermetallic compounds, and A> 1.2 × 10 to ²⁶ (a
Equation 3 is obtained by rearranging the relationship of t% / (n / m ² )).

[0019]

(Equation 24)

When niobium is added to these alloys, α
Since the amount of niobium dissolved in -Zr is 0.6% by weight (refer to * 3 described later), it is considered that the structure of the precipitate in this range is the same as in the case where no precipitate is added. The structure and composition of the precipitates deposited in an alloy obtained by adding 0.5% by weight of niobium to a zirconium alloy containing 0.3% by weight of iron, nickel and chromium were examined. Same as when no niobium was added, but contained niobium. Therefore, zirconium, iron, chromium,
Nickel or zirconium, iron, chromium, nickel, a small microstructure of corrosion susceptibility in an alloy obtained by adding niobium that does not change the crystal structure of the precipitate to a zirconium alloy consisting of tin,

[0021]

(Equation 25)

[0022]

(Equation 26)

When the calculation result on the right side of Equation 4 is 0 or less, the right side is regarded as infinity.

The present invention provides a highly corrosion-resistant zirconium alloy having excellent corrosion resistance even when used in a nuclear reactor.

* 1, Yoshio Nonaka; 1997 Atomic Energy Society, Autumn Meeting Preprints, * 2, Nuclear Engineering Series 8, Irradiation Damage, University of Tokyo Press, * 3, Massalki; Binary alloy Phase Diagrams, 2nd e
dition, vol.3,

[0026]

FIG. 1 is a flow chart of an embodiment in which the method for determining corrosion resistance of a zirconium alloy for a nuclear reactor according to the present invention is applied to a fuel cladding tube manufacturing process.

(1) Zirconium sponge and additional elements are weighed and blended so that iron, nickel, chromium and tin have a predetermined concentration.

(2) An ingot in which alloy components are uniformly melted through a compact press, electrode melting, and multiple melting steps.

(3) After heating the ingot at a high temperature of 1000 ° C. or higher, it is hot forged and processed into a long rod having a smaller diameter.

(4) Further, after heating to the β-phase temperature, water quenching is performed.

(5) Further, cutting, surface shaving, and drilling are performed to produce an extruded billet.

(6) The billet is extruded at a temperature of 600 to 700 ° C. to produce an extruded raw tube.

(7) Further, a raw tube treatment is performed to produce a raw tube.

(8) After heating the raw tube to the β-phase temperature, water quenching is performed.

(9) Further, cold rolling, washing and vacuum annealing are repeated.

(10) Further, the final dimensions are finished by cold rolling.

(11) After performing degreasing and cleaning, final annealing is performed.

(12) After straightening the bend and polishing the inner and outer surfaces, cut into fixed lengths.

(13) Inspect for defects by visual inspection or ultrasonic inspection.

(14) A sample for an electron microscope was prepared from the residual material generated in the step (12), and an iron / chromium-based precipitate and an iron / nickel-based precipitate were observed and analyzed. Determine the average particle size.

(15) The average composition, average particle size, and chemical composition of weighing and blending are substituted into Equations 2 and 3 to determine whether the product satisfies these. 4 and 5 show the results of evaluating the corrosion resistance of products by applying the corrosion resistance determination method of the present invention.

FIG. 4 shows 0.05 to 0.6% iron by weight;
0.05-0.15% chromium, 0.03-0.20%
Is a result of using Equation 3 to determine the corrosion resistance of a zirconium alloy comprising nickel, 0% or more tin, and zirconium as a balance. The left side of the plot indicates that uniform corrosion having a small corrosion sensitivity and a maximum oxide film thickness of less than 20 μm is on the left side, and the right side indicates that there is a possibility that nodular corrosion or oxide film exfoliation may occur due to high corrosion sensitivity and the above (14). If the average particle size measured in the process is on the left side of the plot, the product is considered to have good corrosion resistance.

FIG. 5 shows 0.05 to 0.6% iron by weight;
0.05-0.15% chromium, 0.03-0.20%
This is the result of using Equation 4 to determine the corrosion resistance of a zirconium alloy composed of nickel, 0% or more of tin, niobium, and the balance zirconium.

From the plot, the left side shows uniform corrosion with a small corrosion-sensitive maximum oxide film thickness of less than 20 μm on the left side, and the right side shows that nodular corrosion and oxide film peeling with large corrosion sensitivity are likely to occur. If the average particle size measured in step 14) is on the left side of the plot, the product is considered to have good corrosion resistance.

(16) The product that has passed through the steps (15) becomes a fuel cladding tube.

An example in which the fuel assembly manufactured by the present manufacturing method is applied as a reactor fuel will be described. FIG. 6 is a perspective view of a fuel cladding tube loaded in a boiling water reactor, and it is possible to provide a fuel cladding tube having excellent corrosion resistance by using the alloy obtained by the present manufacturing method.

[0047]

As described above, according to the present invention, the corrosion resistance when a zirconium alloy is used in a nuclear reactor is determined from the alloy composition, the particle size of the precipitate and the composition, whereby the corrosion resistance is improved. A zirconium alloy can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view of an embodiment in which the corrosion resistance determination method of the present invention is applied to a fuel cladding tube manufacturing process.

FIG. 2 is a schematic diagram showing a state in which two kinds of intermetallic compounds, iron and nickel, which precipitate on a Jirikiguchi a-2, are melted out by irradiation with fast neutrons.

FIG. 3 is a diagram showing the correlation between the solid solution constant of the present invention and the amount of corrosion of the Jil power port A-2 fuel cladding tube.

FIG. 4 shows Zr-Sn-0.05 according to the corrosion resistance determination method of the present invention.
-0.6% by weight Fe-0.05-0.15% by weight Cr-
It is a figure which shows the result of having evaluated the corrosion resistance of 0.03-0.2 weight% Ni.

FIG. 5 shows a method for determining corrosion resistance according to the present invention, in which Zr-Sn-Nb-
It is a figure which shows the result of having evaluated the corrosion resistance of 0.05-0.6 weight% Fe-0.05-0.15 weight% Cr-0.03-0.2 weight% Ni.

FIG. 6 is a perspective view of a fuel cladding tube loaded in a light water reactor.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yoshio Nonaka 2163, Narita-cho, Oarai-machi, Higashiibaraki-gun, Ibaraki Japan Within (72) Inventor Yoshinori Eito 2163, Narita-cho, Oarai-cho, Higashiibaraki-gun, Ibaraki Japan Nuclear Fuel Development Co., Ltd.

Claims (22)

[Claims] 1. A zirconium alloy consisting essentially of iron, chromium, nickel and zirconium, or a zirconium alloy consisting essentially of iron, chromium, nickel, tin and zirconium. 2. A zirconium alloy substantially composed of iron, chromium, nickel and zirconium, or a zirconium alloy obtained by adding niobium to a zirconium alloy substantially composed of iron, chromium, nickel, tin and zirconium. ] 3. A zirconium alloy consisting essentially of iron, chromium, nickel and zirconium, or a zirconium alloy consisting essentially of iron, chromium, nickel, tin and zirconium. 4. The iron, 0.07-0.6% by weight,
In a zirconium alloy consisting of 1 to 0.20% nickel, 0.05 to 1.5% chromium, 0 to 2% tin and the balance substantially zirconium: 5. Iron, 0.07-0.6% by weight, 0.0
In a zirconium alloy consisting of 1 to 0.20% nickel, 0.05 to 0.15% chromium, 0 to 2% tin and the balance substantially zirconium: 6. Iron in an amount of 0.07-0.6% by weight,
In a zirconium alloy consisting of 1 to 0.20% nickel, 0.15 to 1.5% chromium, 0 to 2% tin and the balance substantially zirconium: 7. Iron, 0.2-0.6% by weight, 0.08
In a zirconium alloy consisting of ０．２0.20% nickel, 0.05-0.15% chromium, 0-2% tin and the balance substantially zirconium: 8. Iron, 0.07-0.2% by weight, 0.0
In a zirconium alloy consisting of 8 to 0.20% nickel, 0.05 to 0.15% chromium, 0 to 2% tin and the balance substantially zirconium: 9. 0.2-0.6% iron by weight, 0.01
In a zirconium alloy consisting of ０．０0.08% nickel, 0.05-0.15% chromium, 0-2% tin and the balance substantially zirconium: 10. The iron, 0.07-0.2% by weight.
In a zirconium alloy consisting of 01-0.08% nickel, 0.05-0.15% chromium, 0-2% tin and the balance substantially zirconium: 11. Iron, 0.07-0.2% by weight.
In a zirconium alloy consisting of 01-0.08% nickel, 0.05-0.15% chromium, 0-1.2% tin and the balance substantially zirconium, 12. Iron of 0.07 to 0.2% by weight, 0.1 to 0.2% by weight.
In a zirconium alloy consisting of 01-0.08% nickel, 0.05-0.15% chromium, 1.2-2% tin and the balance substantially zirconium: 13. A zirconium alloy substantially composed of iron, chromium, nickel and zirconium, or an alloy obtained by adding niobium to a zirconium alloy substantially composed of iron, chromium, nickel, tin and zirconium. 14. An iron, 0.07-0.6% by weight.
A zirconium alloy consisting of 01-0.20% nickel, 0.05-1.5% chromium, 0-2% tin and the balance substantially zirconium was added with up to 0.6% by weight of niobium. In the alloy, 15. Iron, 0.07-0.6% by weight.
A zirconium alloy consisting of 01-0.20% nickel, 0.05-0.15% chromium, 0-2% tin and the balance substantially zirconium, with up to 0.6% by weight niobium added. In the alloy, 16. Iron, 0.07-0.6% by weight.
A zirconium alloy consisting of 01-0.20% nickel, 0.15-1.5% chromium, 0-2% tin and the balance substantially zirconium, with up to 0.6% by weight niobium added. In the alloy, 17. Iron at 0.2-0.6% by weight, 0.0
A zirconium alloy consisting of 8 to 0.20% nickel, 0.05 to 0.15% chromium, 0 to 2% tin and the balance substantially zirconium was added with up to 0.6% by weight niobium. In the alloy, 18. The composition of claim 1 wherein the iron content is 0.07-0.2% by weight.
0.6% or less by weight of niobium is added to a zirconium alloy consisting of 08-0.20% nickel, 0.05-0.15% chromium, 0-2% tin and the balance substantially zirconium. In the alloy, 19. Iron, 0.2-0.6% by weight, 0.0
Zirconium alloys consisting of 1-0.08% nickel, 0.05-0.15% chromium, 0-2% tin and the balance substantially zirconium with up to 0.6% by weight of di-off added to the zirconium alloy In the alloy obtained, 20. 0.07 to 0.2% iron by weight, 0.1 to 0.2% by weight.
A zirconium alloy consisting of 01-0.08% nickel, 0.05-0.15% chromium, 0-2% tin and the balance substantially zirconium was added with up to 0.6% by weight of niobium. In the alloy, 21. Iron of 0.07-0.2% by weight, 0.1 to 0.2% by weight.
A zirconium alloy consisting of 01-0.08% nickel, 0.05-0.15% chromium, 0-1.2% tin and the balance substantially zirconium with up to 0.6% by weight niobium In the added alloy, 22. 0.07-0.2% iron by weight, 0.1-0.
A zirconium alloy comprising from 0.01 to 0.08% nickel, 0.05 to 0.15% chromium, 1.2 to 2% tin and the balance substantially zirconium with up to 0.6% by weight niobium In the added alloy,