JPH0723526B2 - Corrosion-resistant hafnium substrate and method for manufacturing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a corrosion-resistant hafnium substrate used for a control rod for a nuclear reactor and a method for producing the same, which has remarkably good corrosion resistance, particularly in high-temperature water. It is a thing.

[Conventional technology]

As is well known, the thermal neutron absorption cross section of metal hafnium and alloys of hafnium is not necessarily large, but it has many peaks in the resonance energy region, so it has effective nuclear properties as a control material for nuclear reactors. It is known that

By the way, at present, a control rod for a BWR (Boiling Water Type Light Water Reactor) is a stainless steel control rod sheath 22 having a cross-shaped cross section and a handle 21 at one end on a Velocity Limiter 20 as shown in FIG. The control rod sheath 22 contains boron carbide (B ₄
The stainless steel thin tubes 23 filled with the powder of C) are arranged. As shown in FIG. 4, this control rod has a fuel rod 25 housed in a fuel channel 24 between each piece of a control rod sheath 22, and the control rod and four sets of fuel rod storing channels are arranged in the control rod sheath 22. Therefore, the unit of the reactor core is constructed, and the fuel rods in the four sets of the channel boxes are controlled by this integral control rod.

In nuclear reactors where such control rods are used, it is desirable to lengthen the operating cycle in order to improve the utilization rate of the plant, and replacement of control rods that have reached the end of their life is a process of periodic inspection of Plato. In addition to the impact, the used control rods generated by the replacement will increase the amount of radioactive waste.Therefore, the operation cycle is extended, the period until the control rods are replaced, the used control It is strongly desired to extend the service life of control rods, such as to reduce rod generation. Based on this demand, it has been proposed to apply a hafnium material, which has excellent corrosion resistance in high temperature water, as a control rod for BWR currently used. For example, in Japanese Examined Patent Publication No. 58-44237, a control rod using hafnium in the upper part of the control rod, that is, the upper part of the wing, and the lateral part, that is, the outer position of the neutron absorbing rod in the sheath, which are easily exposed to high temperature water. Is shown, and in JP-A-56-97897 and JP-A-56-74690,
A control rod using metal hafnium or a hafnium alloy in a plate shape is shown. Further, JP-A-59-38687 discloses that a hafnium tube is used as a neutron absorber.

[Problems to be solved by the invention]

However, although it has been conventionally known that hafnium materials have excellent corrosion resistance in high-temperature water, their corrosion resistance is not sufficient for long-term use such as in BWRs in harsh environments. In addition, there is a problem that the demand for extending the service life of the control rod cannot be fully met.

The present invention basically aims to solve the above-mentioned problems, has extremely excellent corrosion resistance in high-temperature water, and can be used for a long period of time in a harsh environment such as BWR and PWR (pressurized water type light water reactor). And a method for producing the same.

[Means for solving problems]

That is, the corrosion-resistant hafnium substrate of the present invention has V a, V b, VI a, VI b, VII a, VII b and V a on the surface of the hafnium substrate material.
It is characterized in that an oxide film containing one to two or more elements other than nitrogen and oxygen among the group III elements in an atomic percentage of 0.1 to 50% is formed.

The hafnium base material may be either a hafnium-based alloy or a metal hafnium. Further, as the metal hafnium, hafnium of 90 wt% or more and the balance of inevitable impurities can be used.

Further, the method for producing a corrosion-resistant hafnium substrate of the present invention comprises forming an oxygen-deficient oxide film on the surface of a hafnium substrate material, and then forming V a, V b, VI a, VI b, VII on the oxygen-deficient oxide film.
It is characterized by implanting one or more elements of a, VIIb and VIII group elements except nitrogen and oxygen.

The oxygen-deficient oxide film referred to here means that the content ratio of metal ions (M ions) and O ² − ions as metal oxides is lower than that of the stoichiometric integer ratio (MO). _1-
δ; 0 <δ <1) means an oxide film, which is a so-called oxide film that has a fluorite type crystal structure and a boundary that can be clearly distinguished from other metal matrix phases, or from the substrate surface to the inside The oxygen diffusion layer may have any of the oxygen-enriched regions in which the oxygen atom concentration gradually decreases.

The hafnium base material used in the method of the present invention includes:
It may be either a hafnium-based alloy or a metal hafnium.
It is possible to use a material in which the balance is unavoidable impurities in an amount of wt% or more.

Further, the formation of the oxygen-deficient oxide film on the surface of the hafnium substrate can be carried out by autoclave treatment so that the film thickness becomes 0.1 mm or less.

In addition, the formation of the oxide film is carried out at an oxygen partial pressure of 1 × 10 ⁻³ to 1 × 10 ⁴ m
It is possible to heat at a temperature of 500 to 1000 ° C for 1 second to 1 hour in an atmosphere of mHg so as to obtain a film thickness of 0.1 mm or less. It can be carried out in a heating furnace or an infrared furnace or by irradiation with a laser beam or an electron beam.

[Action]

Before describing the operation of the present invention, in order to clarify the details of the present invention, the background of the invention will be described.

The inventors of the present invention have found that the oxide film formed on the surface of the conventional hafnium material has a fluorite type crystal structure as shown in FIG. It was noted that in addition to vacancies and crystal defects such as interstitial cations and interstitial anions, excess electrons, which are electron defects, are included.

That is, all metal oxide films are classified into three types according to whether the content ratio of metal ions (M ions) and O ² -ions is a strict integer ratio (MO). The oxide film formed on the surface of the conventional hafnium material contains a small amount of ions (M ³ +) in the state of low valence in M ⁴ +, so that it may balance the excess of electrons. O ² − is an oxygen-deficient oxide film (MO ₁ −δ) whose molecular formula is less than that of MO, depending on the electrically neutral conditions.
Therefore, as shown in FIG. 6, this oxygen-deficient oxide film has an energy level below the conduction band as in the n-type semiconductor, and electrons excited from this level enter the conductor. Participate in electrical conduction. In such an oxide film,
In the environment of high temperature water or water vapor, electrons are easily excited in the conductor. As the electrons participate in electrical conduction in this way, the electrically neutral condition is broken, and the O ² -ion is taken in from the surrounding environment by the action of balancing this, increasing the thickness of the oxide layer. This process promotes the corrosion of hafnium material.

Therefore, based on such a corrosion process of the hafnium material, the inventors of the present invention have shown that the oxide film formed on the surface of the hafnium-based alloy has a value V a of the element synchronization table in which the electric charge has a charge larger than 4+ of hafnium. , V b, VI a, VI b, VII a, VII b and VIII elements are ion-implanted to remove the semiconducting properties of the oxide film and to remove the O ² -ion oxidation. Considering that the incorporation into the coating can be controlled, we conducted an experiment to ion-implant the above elements into this oxide coating using an ion accelerator, and then conducted a corrosion experiment in an autoclave to show the effect of ion implantation on the corrosion resistance of this oxide coating. I checked. As a result, elements other than nitrogen and oxygen, that is, V a, V b, N b, Ta, V b
P, As, Sb, Bi, VI As a group, Cr, Mo, W, VI b group is S, S
e, Te, Po, Mn, Fe, Re as VIIa group, F, Cl, as VIIb group
Hafnium material having oxide film on the surface by ion implantation of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt as Br, I, At, and VIII groups respectively has significantly improved corrosion resistance The present invention has been made based on such findings.

That is, according to the corrosion-resistant hafnium substrate of the present invention, the oxide film contains an element having a valence higher than 4+ of hafnium, and this element causes excess electrons to be incorporated into the element ion, By reducing the number of electrons excited in the conduction band shown in Fig. 6 and removing the n-type semiconducting property, the uptake of new O ² -ions into the oxide film is controlled, which improves the corrosion resistance. It is inferred that it will improve.

The hafnium base material used in the present invention may be either a hafnium-based alloy or a metal hafnium, and as the metal hafnium, hafnium is 90
If it is more than wt%, the balance is zirconium, iron, oxygen, tantalum,
It is possible to use those containing chromium, tin, etc. as impurities, and it is preferable that zirconium contained as impurities is 4 wt% or less and hafnium is 95 wt% or more. This is because an increase in the content of zirconium causes deterioration of corrosion resistance, and it is easy to reduce the content of zirconium to 4% or less by ordinary economic refining.

Further, the oxide film formed on the surface of the hafnium base material preferably has a thickness of 0.1 mm or less. This has a film thickness of 0.1
This is because if it exceeds mm, the tendency of lowering the ductility increases.

Furthermore, V a, V b, VI a, VI b, VII contained in the oxide film
In addition to the case where a, VII b and VIII group elements are contained evenly over the entire area of the oxide film, in addition to being distributed as a layer in the oxide film or within the oxide film, It may be contained in a predetermined concentration gradient. The point is that, depending on the semiconducting properties of the oxide film on the surface of the hafnium base material, the content aspect and content suitable for removing the oxide film are appropriately determined. Anything can be selected. However, it is appropriate that the content of the element is within the range of 0.1 to 50%. This is because if it is less than 0.1%, the effect of improving the corrosion resistance is insufficient, and if it exceeds 50%, the oxide film becomes brittle.
In order to put the corrosion resistance improving effect and the soundness of the oxide film under higher requirements, the content is preferably within the range of 3 to 20%.

As a means for incorporating the above-mentioned elements into the oxide film on the surface of the hafnium base material, ion implantation with an ion accelerator can be used. With this means, it is possible to inject a desired amount of the element in the form of ions into a desired film thickness portion of the oxide film by changing the acceleration voltage of the accelerator. The type of this ion accelerator is not particularly limited, and various types of ion accelerators can be used, for example, Kotskcroft type accelerator, Handegraph type accelerator and tandem type accelerator can be used.

Also when implanting two or more of the elements, two or more ion sources are prepared according to the elements, and two or more ions can be sequentially or simultaneously implanted by this ion source. Similar to the case of injecting, the effect of improving corrosion resistance can be obtained.

Next, according to the method for producing a corrosion-resistant hafnium substrate of the present invention, one or two or more elements of Va, Vb, VIa, VIb, VIIa, VIIb and VIII elements are added to the hafnium substrate material. By injecting into the oxide film on the surface, the above-mentioned elements are contained in the oxide film on the surface of the hafnium substrate material, and the above-mentioned corrosion-resistant hafnium substrate having excellent corrosion resistance can be obtained.

In the present invention, the oxide film can be formed on the surface of the hafnium base material by various methods. For example, it can be formed by a method of forming by autoclave treatment or a method of forming by heating in various heating furnaces such as an electric furnace, a high-frequency furnace, an infrared furnace, and irradiation with a high-density energy source such as a laser beam or an electron beam. It is also possible to perform the heat treatment by. All of these methods are based on heat treatment, and this heat treatment is preferably carried out by holding at a temperature in the range of 500 to 1000 ° C. This is because the required oxide film is difficult to form at a holding temperature of less than 500 ° C, and the mechanical strength tends to decrease at a holding temperature of more than 1000 ° C due to coarsening of the grain size of the hafnium substrate. This is because. Further, it is desirable that the heat treatment time be within a range of 1 second to 1 hour. This is because it is recognized that the required oxide film is not sufficiently formed when the time is less than 1 second, and the oxide film becomes too thick and the ductility of the hafnium substrate is deteriorated when the time exceeds 1 hour. Further, the heat treatment atmosphere has an oxygen partial pressure of 1 × 10 ⁻³ to 1
It is preferably within the range of × 10 ⁴ mmHg. Outside this range,
That is, if it is less than 1 × 10 ⁻³ mmHg, it becomes difficult to form a required oxide film, and even if the oxygen partial pressure is increased to more than 1 × 10 ⁴ mmHg, the effect of oxide film formation is saturated, which is economically disadvantageous. Because it will be.

〔Example〕

Next, an example of the method for producing the corrosion-resistant hafnium substrate of the present invention will be described.

Hafnium base material has a chemical composition of Zr2.1ppm, Fe
A hafnium-based alloy in which the total amount of Cr and Ni is 100 ppm or less, O is 200 ppm, and the balance is hafnium is used. After this material is melted in vacuum, it is subjected to hot working and cold working to obtain a plate-shaped test piece, which is further vacuum-annealed at 700 to 850 ° C. Next, the surface of this plate-shaped sample was polished with diamond powder having an average particle size of about 25 μm, and further autoclaved (temperature 420 ° C., treatment time 24 hours, pressure 105 kg / cm ² , flow rate 18 /
h, dissolved oxygen amount 0.3-0.4ppm, conductivity <0.2μs / cm, pH 5.8
˜7.0) or electric furnace treatment (about 700 ° C., 760 mmHg) to form an oxide film having a thickness of about 1 μm on the surface of the specimen. Implanted ions of sample Nos. 1 to 56 shown in Table 1 are implanted into this oxide film by using a Cockcroft type ion accelerator. The operating conditions of the ion accelerator used here are an acceleration voltage of 400 KeV and a vacuum degree of the vacuum chamber of the sample chamber of 10 ^-6 to 10 ^-7 to
rr, the temperature is room temperature.

FIG. 1 is a view showing the appearance of this ion accelerator,
FIG. 2 further shows the structure of this device and the path 4 of the ion beam.
It is the conceptual diagram which showed.

To explain this in detail, the ion accelerator stores the element of the ion to be injected in the state of powder in the oven 5a, and heats or evaporates this element, or the ion source 6 is provided by a separately provided gas bottle 5b. And is supplied with a high voltage by the ion source 6 to be generated as implanted ions. The ion beam is irradiated from the accelerator 1 composed of the ion source 6, the mass analyzer 7 and the accelerating tube 8 through the quadrupole lens 2, the deflector 9 and the slit 10 to the sample 11 in the vacuum chamber 3. As a result, the oxide layer hesion on the sample surface is injected. Electromagnet 12, acceleration tube current 13, quadrupole lens power supply 1
4, the deflector current 15, the slit ammeter 16, the target ammeter 17, and the temperature measurement control system 18 are connected to a micro computer 19, and these are controlled by the micro computer 19 so that the implantation conditions are constant. In this embodiment, as shown in Table 1, as the element of the ion to be implanted, a pentavalent, hexavalent, heptavalent and octavalent element and two or more of these elements are used. .1 ~
Implant 1 cm ^{2 of} 10 ¹³ to 10 ¹⁹ ions of No. 58, respectively.

The 56 types of corrosion-resistant hafnium substrates of the present invention produced by the above method and the samples (No. 57, 58) in which the implantation elements were changed to nitrogen and oxygen as comparative materials, and the oxide film which had not been ion-implanted were formed on the surface. The sample (No.59) and the oxide film-formation-treated material (No.60) that had not been subjected to oxide film formation treatment were subjected to a corrosion test under the same conditions. The corrosion resistance performance of the samples was investigated.

In the corrosion test, the corrosion behavior in the actual reactor was simulated, and each sample was immersed in water vapor of 0.5 ppm or less in dissolved oxygen and pH 5 to 7 at 500 ° C and 105 kgf / cm ² for 24 hours. It was done by the method of holding.

The results of this corrosion test are shown in Table 1 (1) and (2), and the corrosion resistance is judged by the amount of corrosion increase. That is, the smaller the corrosion weight increase, the better the corrosion resistance.

According to Table 1 (1) and (2), the hafnium substrate with no oxide film formed (Sample No. 60) and the hafnium substrate with no oxide film formed (Sample No. 59) , A hafnium substrate (sample Nos. 1 to 31) in which pentavalent, hexavalent, hexavalent, and octavalent ions excluding nitrogen and oxygen were implanted into the oxide layer formed on the surface and two or more of these ions were implanted. Hafnium substrate of the example (Sample No. 32
~ 56), the corrosion amount is large and the corrosion resistance is poor.
That is, it is clear that the hafnium substrates of the examples have remarkably reduced corrosion increments as compared with the conventional ones, and are extremely excellent in corrosion resistance. Further, such improvement in corrosion resistance is not affected by the method for forming an oxide film before ion implantation, and an effect of improving corrosion resistance is recognized regardless of the method of forming the oxide film. It should be noted that no improvement in corrosion resistance could be obtained in the case where nitrogen or oxygen was injected into the oxide film (Sample Nos. 58 and 59).

From the above points, an oxide film is provided on the surface of the hafnium base material, and the oxide film contains pentavalent elements (V a and V b group elements in the periodic table) excluding nitrogen and oxygen, and hexavalent elements (VI a, VI
It has been clarified that a hafnium substrate having extremely excellent corrosion resistance can be provided by containing a b-group element), a 7-valent element (VIIa, VIIb-group element), and an 8-valent element (VIII-group element).

In addition, in this Example, a part of Sample Nos. 32 to 56 was shown as containing two or more kinds of elements in the oxygen coating film, but the present invention is not limited to this. Value,
It may be one containing two or more kinds of 7-valent and 8-valent elements, and the effect of improving the corrosion resistance can be obtained in the same manner as described above.

(Effects of the Invention) As described above, according to the present invention, it is possible to obtain a hafnium substrate having excellent corrosion resistance in high-temperature water, for example, as a control rod material for a reactor such as BWR or PWR in a severe operating environment. By using it, the period of use in the nuclear reactor can be made very long, and there is an effect that the plant utilization rate can be improved and the amount of radioactive waste generated can be reduced.

[Brief description of drawings]

FIG. 1 is an external view showing an example of an ion accelerator using one embodiment of the method of the present invention, FIG. 2 is a schematic view showing the structure of the ion accelerator and the ion beam path, and FIG.
FIG. 4 is a perspective view showing a control rod for a nuclear reactor, FIG. 4 is a plan view showing a fuel assembly and a control rod, FIG. 5 is a schematic diagram showing a crystal structure of an oxide film formed on the surface of a conventional hafnium material, Sixth
Similarly, the figure is a schematic diagram showing the energy band and electronic state of the oxide film. 1 ... Ion accelerator, 1 ... Sample, 22 ... Control rod sheath, 23 ... Stainless steel thin tube, 25 ... Fuel rod.

Claims (10)

[Claims] 1. A surface of a hafnium substrate is provided with V a, V b, VI
a, VI b, VII a, VII b, and VIII elements of one or more elements excluding nitrogen and oxygen in percentage of base paper of 0.
A corrosion-resistant hafnium substrate, characterized in that an oxide film containing 1 to 50% is formed. 2. The corrosion-resistant hafnium substrate according to claim 1, wherein the hafnium substrate material is a hafnium-based alloy. 3. The hafnium base material is 90 wt% hafnium.
%. The corrosion-resistant hafnium substrate according to claim 1, wherein the hafnium metal is a metal hafnium, the balance of which is unavoidable impurities with a content of at least%. 4. An oxygen-deficient oxide film is formed on the surface of a hafnium base material, and then V a,
A method for producing a corrosion-resistant hafnium substrate, which comprises injecting one or more elements of V b, VI a, VI b, VII a, VII b and VIII elements other than nitrogen and oxygen. 5. The method for producing a corrosion-resistant hafnium substrate according to claim 4, wherein the hafnium substrate material is a hafnium-based alloy. 6. The hafnium substrate is 90 wt% hafnium.
The method for producing a corrosion-resistant hafnium substrate according to claim 4, characterized in that it is a metal hafnium, the balance of which is unavoidable and the balance is unavoidable impurities. 7. The formation of the oxygen-deficient oxide film on the surface of the hafnium substrate is 0.1 mm by autoclave treatment.
The method for producing a corrosion-resistant hafnium substrate according to any one of claims 4 to 6, which is performed so as to have the following film thickness. 8. The formation of an oxygen-deficient oxide film on the surface of the hafnium substrate is performed by oxygen partial pressure of 1 × 10 ⁻³ to 1 × 10 ⁴ mmHg.
7. Atmosphere of 1 to 1 hour at a temperature of 500 to 1000 [deg.] C. in order to obtain a film thickness of 0.1 mm or less. The method for producing a corrosion-resistant hafnium substrate according to item 1. 9. The heating at a temperature of 500 to 1000 ° C. is carried out in any one of an electric furnace, a high frequency heating furnace, an electric heating furnace, and an infrared furnace.
A method for producing a corrosion-resistant hafnium substrate according to the above item. 10. The method for producing a corrosion-resistant hafnium substrate according to claim 8, wherein the heating at a temperature of 500 to 1000 ° C. is performed by irradiation with a laser beam or an electron beam.