KR101075573B1 - Method of forming micro/nano structure on surface of nuclear fuel rod cladding having zirconium - Google Patents

Abstract

According to an embodiment of the present invention, a method of forming a micro-convex surface of a cladding surface of a nuclear fuel rod including zirconium includes: placing a cladding of the nuclear fuel rod on a first pole to connect a positive electrode, and placing a conductor plate on a second pole. Connecting, immersing the cladding of the fuel rods in an electrolyte solution, and applying a voltage to the positive and negative electrodes to cause an oxidation reaction on the cladding surface of the fuel rods. At this time, the temperature of the electrolyte solution is characterized in that to maintain 10 ℃ or less.

Nuclear Fuel Rod, Zircaloy, Cladding, Fine Iron, Critical Heat Flux

Description

METHOD OF FORMING MICRO / NANO STRUCTURE ON SURFACE OF NUCLEAR FUEL ROD CLADDING HAVING ZIRCONIUM}

The present invention relates to a method of treating a cladding surface of a nuclear fuel rod.

Zirconium has a melting point of 1,852 degrees Celsius and is chemically stable, and has a very strong resistance to corrosion from the outside. For this reason, zirconium or its alloys and oxides are used in non-corrosive items such as fuel rod coatings, rust-resistant ceramic kitchen utensils, and tools for handling chemicals in nuclear power plants.

On the other hand, the nuclear fuel is wrapped in aluminum or magnesium film so that the waste generated in the nuclear fission process is mixed with the coolant so that it does not leak out. In the case of a light water reactor, low-concentration uranium dioxide (UO ₂ ) powder is molded and sintered into a cylindrical tablet having a diameter of 2 cm and a height of 2 cm to make a pellet of dark brown, which is made of a zircaloy which has good corrosion resistance against high temperature cooling water. Place in a thin metal tube, approximately 3 mm in diameter, and seal both ends.

Usually, a bundle of tens or hundreds is used to make a fuel assembly and use it as a unit. There are hundreds of such assemblies in a reactor. The cladding tube is made less than 1mm thick for good thermal conduction. In nuclear fission, the center temperature of fuel pellets is about 200 ℃, the surface temperature is 600 ℃, and the inner and surface temperatures of nuclear fuel rods are about 400 ℃ and 300 ℃, respectively.

As such, the rods that are exposed to high temperatures may be severely exposed to fission products when they are ruptured, causing serious problems. Therefore, efforts to increase their stability are constantly needed.

Based on the technical background as described above, the present invention is to provide a method for forming fine iron on the surface so that the cladding surface containing zirconium has a hydrophilic to increase the stability of the nuclear fuel rods used in nuclear power plants.

According to an embodiment of the present invention, a method of forming a micro-convex surface of a cladding surface of a nuclear fuel rod including zirconium includes: placing a cladding of the nuclear fuel rod on a first pole to connect a positive electrode, and placing a conductor plate on a second pole. Connecting, immersing the cladding of the fuel rods in an electrolyte solution, and applying a voltage to the positive and negative electrodes to cause an oxidation reaction on the cladding surface of the fuel rods.

At this time, the temperature of the electrolyte solution is characterized in that to maintain 10 ℃ or less. The method may be performed while maintaining the temperature of the electrolyte solution within a range of 0 ° C to 10 ° C.

The electrolyte solution may be used a hydrofluoric acid (HF) solution in the range of 0.01 to 1.0% by weight.

The voltage applied to the positive electrode and the negative electrode may be set to be in the range of 20V to 40V to perform the method.

The time for applying the voltage to the positive electrode and the negative electrode may be set to fall within the range of 10 minutes to 30 minutes to perform the method.

According to the method of forming the fine iron on the surface of the nuclear fuel rod cladding containing zirconium as described above, it is possible to form a hydrophilic oxide film having a microstructure formed on the surface of the zirconium and zirconium alloys inexpensively as compared to a method such as MEMS through anodization.

In addition, since it is possible to process a large surface of the curved surface through anodization, it is possible to easily produce a cylindrical surface such as a nuclear fuel rod hydrophilic surface.

As the fuel rod cladding surface is formed as a hydrophilic surface, the heat transfer efficiency increases as the contact angle to the liquid decreases, thereby increasing the efficiency of the nuclear power plant.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. In order to clearly illustrate the present invention, parts not related to the description are omitted, and the same or similar components are denoted by the same reference numerals throughout the specification.

According to a preceding study (Kandlikar, S, G., 2001, "A Theoretical Model to Predict Pool Boiling CHF Incorporating Effects of Contact Angle and Orientation," Journal of Heat Transfer, Vol. 123, pp. 1071-1079.) The critical heat flux (CHF) increases as the surface of the heater approaches hydrophilicity in a boiling heater. The critical heat flux refers to the point where the surface temperature of the heater rises rapidly without increasing the heat flux moving to the fluid when the heat flux is increased while the heater is operating. If the heating continues excessively at this point, the heater does not overcome the heat and breaks down, so the actual heat engine operates at a lower level than the critical heat flux point for safety.

Increasing the critical heat flux point through surface modification allows the heat engine to operate at higher temperatures, which increases energy efficiency according to the Rankine cycle principle. In addition, even if the actual operating temperature is not increased, the difference between the heat flux and the critical heat flux at the time of operation becomes large, so that there is an advantage of higher stability.

By applying this principle to a nuclear power plant, the cladding surface of a nuclear fuel rod exposed to high temperature can be made into a hydrophilic surface, thereby increasing the critical heat flux point and consequently obtaining higher stability.

FIG. 1 is a schematic diagram illustrating a fuel rod constituting a fuel assembly used in a nuclear power plant, and FIG. 2 is a schematic diagram illustrating a fuel assembly used in a nuclear power plant.

Nuclear fuel rods 10 containing uranium dioxide (UO ₂ ) pellets (sintered bodies) are arranged in a 16x16 can be fixed by a spacer grid (21, 23) to achieve the fuel assembly (20). The nuclear fuel rod 10 is made of a cylindrical, likewise a plurality of pellets (12) made of a cylindrical is stacked therein, the compression spring (top) to prevent the movement of the pellet 12 in the nuclear fuel rod (10) 15) can be inserted.

The cladding 17 forming the shell of the nuclear fuel rod 10 may be made of a zirconium alloy (zircaloy), which is an alloy of zirconium and tin mixed with chromium and iron.

Meanwhile, in order to make the surface of the solid hydrophilic, there are a method of changing the chemical properties of the surface and a method of changing the surface shape at the micro scale or the nano scale. In the embodiment of the present invention, the surface shape at the micro scale or the nano scale is used. Adopt ways to change

That is, in this embodiment, by applying anodization to the cladding of the nuclear fuel rod, it is possible to form a micro / nano-scale structure on the surface while electrochemically promoting the oxidation of the cladding surface. Such anodization is basically cheaper than the MEMS (microelectromechanical system) process using photolithography, which requires a clean facility, which requires a lot of investment, and is difficult to apply to large areas or curved surfaces. There is an advantage.

In order to apply the anodic oxidation method to the cladding surface of the fuel rod containing zirconium, first, the cladding of the fuel rod is placed on the first pole to connect the anode, and the conductor plate is placed on the second pole to connect the cathode. As the conductive plate connected to the negative electrode, a conductive plate made of platinum may be used.

Then, the nuclear fuel rod cladding connected to the positive electrode and the conductor plate connected to the negative electrode are immersed in the electrolyte solution. As the electrolyte solution, a hydrofluoric acid (HF) solution in the range of 0.01 to 1.0% by weight can be used. In hydrofluoric acid solution of less than 0.01% by weight, the rate of oxidation reaction is too slow to be practically applied, and in hydrofluoric acid solution of more than 1.0% by weight, the oxide film of the fuel rod cladding is peeled off to give the effect of electropolishing. Can't make it.

Then, when a voltage is applied to the anode and the cathode, an oxidation reaction starts at the cladding surface of the fuel rod.

At this time, by adjusting the temperature of the external cooling water to change the temperature causing the oxidation reaction, the temperature of the electrolyte solution can be maintained at 10 ℃ or less, it can be maintained in the range of 0 ℃ to 10 ℃. If the temperature of the electrolyte solution is less than 0 ° C., the rate of oxidation reaction is too slow to be practically applied. If the temperature is maintained above 10 ° C., the oxide film of the fuel rod cladding is peeled off, and thus a hydrophilic surface cannot be formed.

In addition, the voltage applied to the positive electrode and the negative electrode can be selected and applied within the range of 20V to 40V, the time for applying the voltage to the positive electrode and the negative electrode can be set to fall within the range of 10 minutes to 30 minutes. If the applied voltage is less than 20V, the oxidation reaction is too slow to be practically applied. If the applied voltage is more than 40V, the oxide film of the fuel rod cladding is completely peeled off, thereby producing an electropolishing effect, and thus a hydrophilic surface cannot be made. In addition, when the reaction time is less than 10 minutes, the wettability of the surface of the fuel rod cladding formed is not sufficient, and when the reaction time exceeds 30 minutes, the oxide film of the fuel rod cladding is peeled off, so that a hydrophilic surface cannot be formed.

When the anodization process is performed on the cladding surface of the nuclear fuel rod containing zirconium in the above manner, the cladding surface exhibits a small hydrophilicity with a contact angle of about 10 degrees. The contact angle is a measure of the angle between the surface of the droplet and the solid surface to which the droplet is attached, while the droplet is usually attached to a solid surface such as a metal.

[Experimental Example]

A fuel rod cladding made of a zirconium alloy was connected to the positive electrode, and a platinum plate was connected to the negative electrode, and anodization was performed using a hydrofluoric acid (HF) solution as an electrolyte solution. At this time, as shown in Table 1 was carried out while varying the concentration of the electrolyte solution, the temperature of the electrolyte solution, the applied voltage and the reaction time.

TABLE 1

division Electrolyte Solution Electrolyte Solution Temperature Applied voltage Reaction time Contact angle Example 1 0.5wt% HF 10 ℃ 30 V 30 minutes 8 degrees Example 2 0.5wt% HF 10 ℃ 30 V 20 minutes 10 degrees Example 3 0.5wt% HF 10 ℃ 15 V 60 minutes 12 degrees Comparative Example 1 No anodization 70 degrees Comparative Example 2 0.5wt% HF 25 ℃ 5 V 20 minutes 78 degrees Comparative Example 3 0.1wt% HF 25 ℃ 5 V 30 minutes -

That is, Examples 1 to 3 were carried out by changing the applied voltage to 30V or 15V while maintaining a 0.5% by weight hydrofluoric acid solution at 10 ℃, and set the reaction time to 30 minutes, 20 minutes, 60 minutes respectively.

Comparative Example 1 did not perform anodization at all, and Comparative Examples 2 and 3 varied the concentration of the hydrofluoric acid solution to 0.5% by weight or 0.1% by weight while maintaining the temperature of the electrolyte solution at room temperature (25 ° C). Was 5V, and the reaction time was set to 20 minutes and 30 minutes, respectively.

The results of Example 1 are shown in FIGS. 3 and 4, and the results of Examples 2 and 3 are shown in FIGS. 5 and 6, respectively. In addition, Comparative Example 1 is shown in FIG. 7, and Comparative Examples 2 and 3 are shown in FIGS. 8 and 9, respectively.

In comparison with Comparative Example 1 (not anodizing), it can be confirmed that in Examples 1 to 3, various patterns of micro / nano structures were formed on the surface.

8 and 9, in Comparative Examples 2 and 3, the oxide film was peeled off and no micro / nano structure was observed. . In particular, in Comparative Example 3, the contact angle could not be measured because the oxide film was partially peeled off to form a non-uniform surface.

When comparing the contact angle on the surface of Comparative Example 1 with the contact angle on the surface of Example 1 with reference to FIGS. 10 and 11, in Comparative Example 1 the contact angle is measured about 70 degrees, while in Example 1 About 8 degrees were measured, and Examples 2 and 3 were measured at 10 degrees and 12 degrees, respectively.

Therefore, it was confirmed that the surface of the nuclear fuel rod cladding containing zirconium was changed to a hydrophilic surface through anodization.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Of course.

1 is a schematic diagram illustrating a nuclear fuel rod constituting a fuel assembly used in a nuclear power plant.

2 is a schematic diagram illustrating a fuel assembly used in a nuclear power plant.

3 is a SEM picture of 10,000 times the surface of the zirconium alloy anodized by the method according to Example 1 of the present invention.

4 is a SEM picture of 80,000 times of the surface of the zirconium alloy anodized by the method according to Example 1 of the present invention.

5 is a SEM picture of 80,000 times the surface of the zirconium alloy subjected to anodization by the method according to Example 2 of the present invention.

6 is a SEM picture of 80,000 times of the surface of the zirconium alloy subjected to anodization by the method according to Example 3 of the present invention.

7 is a SEM photograph of 10,000 times the surface of the zirconium alloy (Comparative Example 1) not treated by anodization.

FIG. 8 is an SEM picture of 80,000 times of the surface of the zirconium alloy subjected to anodization under the conditions of Comparative Example 2. FIG.

9 is an SEM picture of 80,000 times the surface of the zirconium alloy subjected to anodization under the conditions of Comparative Example 3.

10 is a photograph showing a state in which a contact angle is measured on a surface of a zirconium alloy according to Comparative Example 1. FIG.

11 is a photograph showing a state in which the contact angle is measured on the surface of the zirconium alloy according to Example 1 of the present invention.

Claims (7)

A method of modifying a cladding outer surface of a nuclear fuel rod comprising zirconium, Positioning a cladding of the nuclear fuel rod on a first pole to connect a positive electrode, and placing a conductor plate on a second pole to connect a negative electrode; Dipping the cladding of the fuel rod into an electrolyte solution containing hydrofluoric acid (HF); And Applying a voltage to the anode and the cathode to cause an oxidation reaction on the cladding outer surface of the fuel rod to make the outer surface of the cladding a hydrophilic surface; Micro-convex formation method of the cladding surface of the nuclear fuel rod containing zirconium containing. The method of claim 1, The temperature of the electrolyte solution is maintained at 10 ° C or less method for forming fine grains on the cladding surface of the nuclear fuel rod containing zirconium. The method of claim 2, The method of forming fine irregularities on the cladding surface of the nuclear fuel rod containing zirconium, characterized in that the temperature of the electrolyte solution is maintained in the range of 0 ℃ to 10 ℃. The method of claim 1, The electrolyte solution is fine iron forming method of the cladding surface of the nuclear fuel rod containing zirconium, characterized in that the hydrofluoric acid (HF) solution in the range of 0.01 to 1.0% by weight. The method of claim 1, The voltage applied to the positive and negative electrodes is in the range of 20V to 40V fine fine iron forming method of the cladding surface of the nuclear fuel rod containing zirconium. The method of claim 5, The time for applying a voltage to the positive electrode and the negative electrode is in the range of 10 minutes to 30 minutes fine fine iron forming method of the cladding surface of the nuclear fuel rod containing zirconium. A nuclear fuel rod in which fine irregularities are formed on a cladding surface by the method according to any one of claims 1 to 6.

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