JP2002277436A - Hydrogen absorption characteristic decision method of zirconium alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydrogen absorption characteristic decision method of zirconium alloys by enabling evaluation with a simple method and in a shorter time. SOLUTION: In the hydrogen absorption characteristic decision method of zirconium alloys, peak areas of two or one current peaks that appear on a polarization curve when the zirconium alloy undergoes an anode polarization are made numerical and the hydrogen absorption characteristic of the zirconium alloy is evaluated from the sum of the peak areas of the two or one peaks.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for evaluating the hydrogen absorption characteristics of a zirconium alloy. More specifically, the present invention relates to a method for determining the hydrogen absorption characteristics of a zirconium alloy used in a nuclear reactor, which allows a simple and short time evaluation of the hydrogen absorption characteristics before actually using the reactor in a nuclear reactor. Things.

[0002]

2. Description of the Related Art At present, zirconium alloys are widely used as fuel cladding tubes and core structural materials in boiling water reactors, pressurized water reactors and the like. Until now, the most commonly used zirconium alloys are zircaloy-2 (Sn 1.2-1.7% by weight, Fe 0.07-
0.20% by weight, Cr 0.05-0.15% by weight, N
i 0.03 to 0.08 wt%, balance Zr) and Zircaloy-4 (Sn 1.2 to 1.7 wt%, Fe 0.1
8 to 0.24% by weight, Cr 0.07 to 0.13% by weight, balance Zr), but also Zr-2.5% Nb,
Zr-1% Nb alloy and the like have also been applied to nuclear reactors.

[0003]

The above alloy is an alloy developed mainly in consideration of neutron economy and corrosion resistance.
At present, fuel burnup is being promoted to improve the economics of nuclear power plants, and the residence time of a reactor fuel assembly in a reactor is prolonged. It has been pointed out that the prolonged residence time of the fuel assembly in the furnace increases the amount of hydrogen absorbed by the zirconium alloy base material and may cause the structural material to become brittle. Under the current operating conditions, it has excellent hydrogen absorption characteristics, but hydrogen injection into the reactor water supply system,
There is a concern that the amount of hydrogen absorption will further increase due to changes such as thinning of material members.

[0004] Therefore, development of a zirconium alloy having a small amount of hydrogen absorption is urgently required even under high burn-up and hydrogen injection conditions. In the development of such an alloy, a method for simply and quantitatively evaluating the hydrogen absorption characteristics is required. However, at present, such an evaluation method has not been established, and in most cases, the soundness of the zirconium alloy is confirmed by long-term use in a real environment or long-term trial in an environment similar to the real environment. is there. Such long-term use and trials in similar environments require a great deal of time, labor and development funding, such as test preparation, actual testing and post-test evaluation, and results in preventing rapid material development. Has become. Thus, there is a need for an evaluation method for easily determining the hydrogen absorption characteristics of a zirconium alloy at high burnup or during long-term use before use.

Hitherto, the evaluation of the amount of hydrogen absorbed has mainly been performed by a corrosion test using an autoclave or a hydrogen absorption test in a hydrogen gas atmosphere. For example, ASTM G2 corrosion test (400 ° C., in 10.3 MPa steam × 72 h) and two-step corrosion test (410 ° C., in 10.3 MPa steam ×
It is evaluated by measuring the amount of hydrogen absorbed in a corrosion test such as 8h + 510 ° C. in 10.3 MPa steam × 16 h). However, the evaluation methods using these autoclaves have a problem that the test time of the autoclave is prolonged especially when long-term use is assumed. Furthermore, the autoclave test itself is performed under various conditions such as water quality, temperature, pressure, and test time, and there is a problem that the test conditions are not yet unified.

[0006] An evaluation method based on microstructure observation is also known. More specifically, Zr ₂ (Fe, Ni) and Zr (Fe, Ni) precipitated as intermetallic compounds in a zirconium alloy.
Cr) This is an evaluation method for evaluating the correlation between the particle size of the type ₂ precipitate and corrosion resistance. Although this method is one of the effective methods for evaluating corrosion resistance, the correlation between hydrogen absorption characteristics and precipitates is still not clear, and is insufficient as an evaluation method for hydrogen absorption characteristics.

As described above, at this stage, there is almost no method for simply and quickly evaluating the hydrogen absorption characteristics of a zirconium alloy before actually using it in a nuclear reactor.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the conventional methods, such as that the test is large, costly and time-consuming, and that the test methods are not uniform.
An object of the present invention is to provide a method capable of evaluating the hydrogen absorption characteristics of a zirconium alloy with a simple operation and in a short time.

Therefore, the method for determining the hydrogen absorption characteristics of a zirconium alloy according to the present invention quantifies the peak area of one or two current peaks appearing on the polarization curve when the zirconium alloy is anodically polarized, and the two or one It is characterized by evaluating the hydrogen absorption characteristics of the zirconium alloy from the sum of the peak areas of the peaks.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to achieve the above object, the present inventor paid attention to an anodic polarization curve, and found that the following relationship exists between a current peak appearing on the curve and the hydrogen absorption amount.

That is, when anodic polarization of Zircaloy 2 in a strong acid, two current peaks were observed, and it was found that the larger the area sum of these two peaks, the smaller the amount of hydrogen absorption. That is, the current peak area can be obtained from the anodic polarization curve, and the hydrogen absorption characteristics of Zircaloy 2 can be evaluated based on the size of the current peak area.

Hereinafter, the method of the present invention will be described in detail.

In the present invention, first, an anodic polarization curve is measured. For example, an anodic polarization curve is measured in 5% H ₂ SO ₄ at 25 ° C. When measuring anodic polarization, it is particularly preferable to use a H ₂ SO ₄ solution having a concentration of 1 to 10%, but it is also possible to use strongly acidic HCl or the like.

The test water such as H ₂ SO ₄ is degassed with an inert gas, preferably Ar gas, before and during the test. FIG. 1 shows an example of the anode polarization curve. Usually, the horizontal axis indicates the current density (A / m ² ), and the vertical axis indicates the potential. In this example, the electric potential indicates an electric potential with respect to SCE (saturated luster electrode).

Next, the area of the peak portion of the current appearing on the anodic polarization curve is determined. When anodic polarization of Zircaloy 2 in 5% H ₂ SO ₄ , current peaks are observed at two places. FIG. 1 shows peaks A and B, respectively.
Peak A is 1.2V vs SCE, Peak B is 1.9V
vs SCE. These two peaks have different peak area ratios and peak area sizes depending on the composition of Zircaloy 2 and the size of the precipitates. In some cases, no peaks are observed.

Next, the respective peak areas are determined by image analysis. An example of how to determine the peak area will be described. Since the anodic polarization curve is usually expressed in logarithm, the logarithmic expression is converted to an absolute value in order to calculate an accurate area. The area of the peak portion is determined as the area surrounded by the base line and the peak curve in the anode curve expressed in absolute value. The area of this peak can be determined by image analysis.

The peak B observed around 1.9 V
In the case of, the baseline may change significantly due to the influence of another peak which is considered to be due to the oxidation reaction of zirconium in a high voltage region. Therefore, it is desirable to set a straight line obtained by extrapolating the low voltage side baseline to the high voltage side as the baseline. FIG. 2 shows an enlarged peak portion of the anode polarization curve of FIG. Regarding the peak B observed near 1.9 V, a straight line obtained by extrapolating the low voltage base line to the high voltage side is defined as the base line, and is surrounded by this base line and a straight line where the voltage becomes V = 2.4 V. The area of the portion to be removed was defined as the peak area. It is necessary to evaluate the two peak areas by graphing the X axis and the Y axis of the graph on the same scale.

Next, the correlation between the peak area obtained by this method and the amount of hydrogen absorption was examined. FIG. 3 shows the results. The abscissa represents the peak areas of the two peaks A and B, respectively, and the logarithmic sum thereof is taken. The hydrogen absorption amount on the vertical axis is 400 ° C, 1
The hydrogen absorption of a sample corroded in 0.3 MPa steam for about 1100 h is measured and shown as a relative value. As is apparent from FIG. 3, the larger the logarithmic sum of the peak areas of the two peaks A and B obtained when the zircaloy 2 is anodically polarized at room temperature in 5% H ₂ SO ₄ , the smaller the hydrogen absorption amount becomes. I understood.

Using the correlation shown in FIG. 3, it is possible to very easily examine the hydrogen absorption characteristics of the material by examining the anodic polarization curve and evaluating the peak area.

[0020]

EXAMPLE An example of investigating the hydrogen absorption characteristics of an improved zirconium-based alloy using the determination method of the present invention will be described. The improved zirconium-based alloy has the following composition.
Alloy L: Chemical composition: Sn; 1.35% by weight, Fe;
0.18% by weight, Ni: 0.07% by weight, Cr: 0.1
A zirconium-based alloy having 1% by weight and the balance being Zr.

Alloy M: Chemical composition: Sn: 1.50% by weight, Fe: 0.25% by weight, Ni: 0.05% by weight, C
r: a zirconium-based alloy having 0.10% by weight and the balance being Zr.

Both alloys L and M were manufactured by the following manufacturing method.

The melted ingot is hot forged (70
0-750 ° C), solution treatment (about 1000 ° C for several hours)
After that, it is cut, surface ground, and drilled to form an extruded billet. Extruded billet is 600-7
It is formed into an extruded tube by hot extrusion at 00 ° C. As a β-quench treatment for improving the corrosion resistance, the outer surface is heated to an α + β region (around 930 ° C.) by high-frequency heating while cooling by flowing water inside the tube,
So-called outer hardening of the tube was performed. Thereafter, cold rolling and annealing are alternately repeated three times to form a fuel cladding tube.

FIG. 4 shows the amount of hydrogen absorbed after the corrosion test of the improved zirconium-based alloy in steam at 400 ° C. and 10.3 MPa (after the corrosion test for about 1100 hours), and the hydrogen absorption characteristics by the evaluation method of the present invention. The result of evaluating is shown. As stipulated in the present invention, that is, it is considered that the larger the logarithmic sum of the peak areas of the two current peaks A and B appearing on the anodic polarization curve, the smaller the hydrogen absorption amount is, but as shown in FIG. In addition, as a result of an actual corrosion test, it was confirmed that a material having a larger logarithmic sum of peak areas had a smaller hydrogen absorption.

The evaluation method of the present invention has shown that the hydrogen absorption characteristics of a zirconium alloy used in a nuclear reactor can be evaluated in a simple manner and in a short time.

[0026]

According to the evaluation method of the present invention, it is possible to evaluate the hydrogen absorption characteristics of a zirconium alloy used in a nuclear reactor in a simple manner and in a short time. Further, this evaluation method can be used for developing a zircaloy alloy having a small hydrogen absorption.

[Brief description of the drawings]

FIG. 1 is an anodic polarization curve. The abscissa indicates the current density on a logarithmic axis, and the ordinate indicates the voltage with respect to SCE (saturated luster electrode).

2 is an enlarged view of a peak current density, FIG. 2 (a) is an enlarged view of a peak A in FIG. 1, and FIG. 2 (b)
2 is an enlarged view of a peak B in FIG.

FIG. 3 is a diagram showing a correlation between a peak area and a hydrogen absorption amount. The horizontal axis represents the logarithmic sum of the two peak areas (corresponding to the shaded portions) shown in FIG.
The hydrogen absorption after corrosion for about 1100 hours in 0.3 MPa steam is shown as a relative value.

FIG. 4 is a graph comparing the hydrogen absorption amounts and peak areas of two materials (alloys L and M) subjected to a corrosion test in steam at 400 ° C. and 10.3 MPa. The Y axis indicates the relative value of the hydrogen absorption amount, and the Y2 axis indicates the logarithmic sum of the peak areas.

Claims (5)

[Claims] 1. The peak area of one or two current peaks appearing on a polarization curve when an anodically polarized zirconium alloy is quantified, and the hydrogen absorption characteristic of the zirconium alloy is calculated from the sum of the peak areas of the one or two peaks. A method for determining the hydrogen absorption characteristics of a zirconium alloy, characterized by evaluating 2. The peak area of one or two current peaks appearing on a polarization curve when the zirconium alloy is anodically polarized, and the hydrogen absorption characteristic of the zirconium alloy is calculated from the sum of the peak areas of the one or two peaks. Is obtained in advance, characterized by evaluating the hydrogen absorption characteristics of the zirconium alloy by comparing the index and the sum of the peak area of the zirconium alloy for hydrogen absorption characteristics determination, characterized in that the zirconium alloy Method for determining hydrogen absorption characteristics. 3. The method according to claim 1, wherein a sum of peak areas is obtained by a logarithmic sum of peak areas. 4. The method according to claim 1, wherein the anodic polarization is performed with an aqueous solution of H ₂ SO ₄ , wherein the hydrogen absorption characteristics of the zirconium alloy are determined. 5. The method according to claim 1, wherein the anodic polarization is performed with an aqueous solution of H ₂ SO ₄ , wherein the anodic polarization is about 1.2 V vs. SCE and about 1.9 V vs. 1.9 V.
A method for determining hydrogen absorption characteristics of a zirconium alloy, wherein a current peak appearing in a potential value of SCE is used.