WO2001033574A1

WO2001033574A1 - Method for improving wettability, and element placed under radiation environment

Info

Publication number: WO2001033574A1
Application number: PCT/JP2000/007680
Authority: WO
Inventors: Tomoji Takamasa
Original assignee: Tomoji Takamasa
Priority date: 1999-11-02
Filing date: 2000-11-01
Publication date: 2001-05-10
Also published as: JP4320412B2; AU1052601A

Abstract

A method for providing a surface having improved wettability which comprises placing a substrate having a coating film of a rutile-type titanium oxide formed on its surface under a η-ray environment to thereby improve the wettability of the surface, or placing a metal substrate having a film of an oxide of the metal formed on its surface under a η-ray environment to thereby improve the wettability of the surface; and a method for improving the heat transfer efficiency of a fuel rod of an atomic reactor, characterized as comprising forming a coating film of a rutile-type titanium oxide or an oxide of a zirconium alloy on the surface of the rod.

Description

Description Method for improving wettability and components placed under radiation environment

The present invention relates to a method for improving the wettability of a member surface, and more particularly to a method for improving the wettability of a member surface by disposing the member in a radiation environment, and an improved wettability. And a member having a surface exhibiting Background art

When a semiconductor material such as titanium oxide is irradiated with ultraviolet light, photoelectrons can be extracted from the surface of the material by a photoelectrode reaction. The chemical reaction of gas-liquid on the contact surface by the photoelectrons is called the so-called photocatalytic reaction. Common uses of titanium oxide photocatalyst include electrolysis, disinfection of contact gas-liquid by oxidation, and self-cleaning. According to the most recent research on physical properties, it has been clarified that this photocatalytic wall reduces the surface tension of the contacting liquid, and as shown in Fig. 1, improves the wettability of the contact surface. The mechanism of super lyophilicity imparted by the photocatalytic effect has not been elucidated clearly, but it has been reported that the photocatalytic effect imparts super lyophilicity to the substrate, for example, as disclosed in Japanese Patent Application Laid-Open No. 11-70. 61, JP-A-2000-75011, JP-A-200-0-87016, and JP-A-2000-119595. On the other hand, recent studies on heat flow have shown that in the boiling phenomenon, which is a general form of heat transfer in plants, a thin liquid film called a micro-mouth liquid film under boiling bubbles has a heat transfer coefficient and nucleate boiling. It has been shown to dominate the phenomenon. The behavior of the liquid film at the mouth of the mixer is greatly affected by surface tension and wettability. Generally, the better the wettability, the more easily the liquid film is formed, and the more stable the heat transfer. Nucleate boiling is achieved.

Therefore, if a wall having good wettability, that is, a wall having lyophilicity can be used for the boiling heat transfer wall, the transition of the nucleate boiling transition condition to the high heat transfer side without heat damage to the wall, that is, Highly efficient nucleate boiling stabilization can be achieved. It is expected that this will enable the plant to achieve significantly higher thermal efficiency.

It is also clear that the better the wettability of the wall, the faster the cooling of the heated wall by condensation. Therefore, for example, if a wall surface having lyophilicity can be used for the wall surface of the containment vessel, the wall surface can be rapidly condensed and cooled in an accident. As a result, stable heat removal is possible, and safety in the event of a nuclear reactor accident is improved.

Titanium oxide acts as a redox catalyst not only by light irradiation but also by irradiation of radiation, as disclosed in JP-A-2-95440, JP-A-8-184689, and JP-A-8-1. No. 83602 and Japanese Patent Application Laid-Open No. H10-2742459. However, there is no research report on the relationship between irradiation and the super-lyophilic phenomenon.

An object of the present invention is to improve the wettability of the member surface by irradiation with radiation.

Another object of the present invention is to improve boiling heat transfer characteristics by improving the wettability of the member surface in a radiation environment such as γ-rays.

Another object of the present invention is to improve the wettability of a member surface in a plant or the like so that the member can be cooled well. Disclosure of the invention The technical means adopted by the present invention to solve the above-mentioned problems is characterized in that a substrate provided with a catalyst layer on the surface is arranged in a radiation environment to improve the wettability of the surface. It is. In this specification, “disposed in a radiation environment” means that the surface of a substrate is irradiated with radiation, the substrate is placed in a space where radiation exists, and the substrate itself has radiation. Includes when the radiation source is inside the substrate and the radiation is supplied from inside to the substrate surface. The radiation is selected from alpha, zero, gamma, x-ray and neutron radiation.

In general, the photocatalytic reaction of titanium oxide occurs with anatase-type titanium oxide, and it is said that photocatalytic reaction under ultraviolet light does not occur with rusyl-type titanium oxide that can withstand higher temperatures. However, it was found that radiation having higher energy than ultraviolet rays (eg, γ-rays) improved wettability. Lucyl-type titanium oxide can withstand higher temperatures than anatase-type titanium oxide, and is therefore advantageous when it is desired to impart wettability to the member surface at high temperatures.

In addition, the surface of titanium metal is usually covered with a thin oxide film due to contact with oxygen in the air. In order to confirm whether the oxide film has a so-called photocatalytic effect, a test piece of metal titanium was prepared. In order to create a more robust oxide film, a test piece was prepared by irradiating the surface with high-temperature plasma and forming an oxide film on the surface with oxygen in the air. As a result of the experiment, it was found that the surface wettability was improved by irradiating the titanium oxide film with radiation. In addition, with respect to zircaloy (zirconium alloy) and stainless copper, improvement in wettability was observed in test pieces having a metal oxide film formed on the surface thereof. The improvement in wettability is considered to be due to the large energy of the radiation, and it is considered that the same effect is exerted on other oxide films. One means of forming an oxide film is to oxidize the surface of the metal substrate to form an oxide film on the surface. In this case, the type of the metal is not limited, and examples thereof include titanium, stainless steel, zircaloy (zirconium alloy), aluminum, lead, and manganese. Means for forming the oxide film is not limited to oxidation of the surface of the metal substrate. As another means, an oxide film may be formed by spraying an oxide on the surface of the base material, or the oxide film may be formed by using sputtering. In this case, the material of the base material is not limited to metal.

The catalyst layer is not limited to these, and other catalysts that exert a so-called photocatalytic effect by irradiation with radiation can be employed. As a result of the experiment, the improvement of the wettability was obtained by irradiating radiation for a long time. In other words, it is thought that the improvement in wettability largely depends on the radiation dose, and when radiation irradiation is stopped, wettability returns to the original. Therefore, advantageously, the present invention is used to impart wettability to a member that is always in a radiation environment. The member that is always under the radiation environment includes a case where the member itself has radiation or a case where a radiation source is present inside the member. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing a change in contact angle when an aluminum plate coated with an anatase type titanium is placed under an ultraviolet ray environment;

In FIG. 2, (A) is a schematic perspective view showing a device for measuring a contact angle of a water droplet using a CCD camera, and (B) is a diagram showing a definition of a contact angle;

In FIG. 3, (A) is a perspective view showing a holder of a test piece used for measuring a contact angle of a water drop, and (B) is a test near a Co 60 source using the holder shown in (A). Perspective view showing a state in which pieces are arranged; Fig. 4 shows the change in wettability of a test piece obtained by spraying a scillated titanium oxide on a stainless steel plate;

Fig. 5 shows the change in contact angle by _y- ray irradiation on a stainless steel sales plate sprayed with Lucyl type titanium oxide;

Fig. 6 shows the change in wettability of a titanium plate specimen with an oxide film formed on the surface;

Fig. 7 shows the change in contact angle due to γ-ray irradiation on a titanium plate with an oxide film formed on the surface;

Fig. 8 compares the change in wettability by gamma irradiation on titanium plate, zircaloy plate, and stainless steel each having an oxide film on the surface; Fig. 9 shows the titanium film with an oxide film on the surface Of contact angle change by y-ray irradiation on sheet, Zircaloy sheet and stainless steel;

FIG. 10 is a diagram showing a boiling characteristic curve;

Fig. 11 shows the experimental equipment for limiting heat flux;

Fig. 12 shows the relationship between the γ-ray irradiation dose and the critical heat flux;

Fig. 13 shows the life of a water drop on a hot surface;

FIG. 14 is a diagram showing a method for comparing the Leidenfrost phenomenon; FIG. 15 is a diagram showing experimental results comparing the Leidenfrost phenomenon before and after performing γ-ray irradiation. Preferred embodiments for carrying out the invention

The present invention improves the wettability of the surface of a substrate having a catalyst layer on the surface thereof by irradiating the surface with radiation. Or an oxide film formed on the surface of the metal substrate. Lucyl-type titanium oxide can withstand higher temperatures than anatase-type titanium oxide. Therefore, a lucyl type oxide that can withstand high temperatures If the wettability is improved by using a tongue, heat transfer characteristics can be improved in an environment such as inside a nuclear reactor.

If the surface of the metal substrate is oxidized to form an oxide film, and the surface is irradiated with radiation to improve wettability, a catalyst layer is formed on the surface of the metal member by forming an oxide film. It can be formed simply by doing.

The present invention, in one preferred example, is applied to members constituting a nuclear reactor. This is because the inside of the reactor is always under the y-ray environment and one of the main components of the present invention, ie, irradiation, is satisfied. The reactor includes a reactor core, a control rod inserted into the reactor core, a reactor vessel containing the reactor core, a shield disposed outside the reactor vessel, and a nuclear reactor provided outside. It consists of a containment vessel that houses the entire furnace. In addition, the reactor core has nuclear fuel, coolant, and moderator. Nuclear fuel is usually used as fuel rods and fuel plates (both are referred to as fuel rods). A fuel rod consists of a number of fuel pellets and a cladding tube containing a number of fuel pellets. In addition, many fuel rods are used as fuel assemblies.

In a nuclear reactor, heat is first generated inside nuclear fuel by fission. This heat is transferred to the cladding tube surrounding the fuel, and the heat transferred to the cladding tube reaches its surface by heat conduction inside the cladding wall. Here, it comes into contact with the coolant flowing outside the fuel rods, heat is transferred to the coolant by heat transfer, and the heat is carried out of the furnace.

As already mentioned, in the boiling phenomenon, which is a general form of heat transfer, a thin liquid film called a micro liquid film under boiling bubbles controls the heat transfer coefficient and the nucleate boiling phenomenon. The behavior of the micro liquid film is greatly affected by the surface tension and wettability, but in general, the better the wettability, the more easily the liquid film is formed, and stable boiling of nucleus with a high heat transfer rate is performed. . Therefore, if the wettability of the fuel rod surface, that is, the cladding tube surface, can be improved, the heat transfer characteristics will be improved. Can be up. Also, in the event of a loss of cooling water in the reactor, when the cooling water inside the reactor decreases, dry patching of the fuel rod surface is difficult. The use of a fuel rod having a surface coated with a rusil-type titanium oxide film improves the wettability of the fuel rod surface by the y-ray in the core. The cladding of fuel rods is usually made of Zircaloy. If an oxide film is formed on the surface of Zircaloy, the wettability of the fuel rod surface will be improved by gamma rays in the core.

It is also clear that the better the wettability of the wall, the faster the cooling of the heated wall by condensation. Therefore, for example, if lyophilicity is given to the wall surface of the reactor vessel, the wall surface can be rapidly condensed and cooled in an accident.

Α. Wettability measurement experiment

A 5 μl drop of water is dropped on the test body, and the contact angle is measured with a CCD camera. As shown in Fig. 2, the experimental apparatus has a CCD camera 1, a movable table 2, a test piece 3 placed on a movable table 2, and illumination light 4, and a water drop 5 is dropped on the test piece 3. And observe with CCD camera 1.

[Experiment 1]

As a preliminary experiment, an ultraviolet irradiation experiment was performed.

The test pieces are the following three.

(1) Aluminum plate, stainless steel plate coated with anatase type titanium oxide, (30 X 30 X 3 ram)

(2) Stainless steel plate (30 X 30 X 3 mm) sprayed with Lucyl type titanium oxide

(3) Titanium plate with oxide film formed on its surface (30 X 30 X 1 mm)

The oxide film is formed by irradiating high-temperature plasma to the titanium surface and forming an oxide film on the titanium surface by oxygen in the air.

Anataze type titanium oxide is coated on stainless steel plate and aluminum plate. The painted test piece changed its coatability due to ultraviolet light (ultraviolet light 400 nm or less). If the test specimen, which has been exposed to ultraviolet rays and has become highly wettable, is placed in an environment where the ultraviolet rays are blocked, the wettability of titanium oxide will decrease. Thereafter, when the ultraviolet rays are again irradiated, the wettability is improved again.

However, no change was observed in the wettability of the test piece having the surface provided with the lucyl type titanium oxide and the test piece having the oxide film formed on the surface. It is considered that this is because the band gap has not been exceeded.

[Experiment 2]

X-ray irradiation experiments were performed at the Co-60 source experimental facility.

The test pieces are the following two.

(1) Stainless steel plate (30 X 30 X 3 mra) sprayed with nolesil-type titanium oxide (2) Titanium plate (30 X 30 X 1 ram) with an oxide film formed on the surface

The experiment was conducted at a facility that can irradiate a very large amount of y-rays in a short time with a dose of 10 to 20 kGy / h. 15 to 20 test pieces 3 are placed on a wooden holder 6 as shown in Fig. 3 (A), and placed near the Co-60 source 7 as shown in Fig. 3 (B). Gamma irradiation was performed. Two continuous irradiation experiments for about 10 days were performed. As a result, there was a large change in wettability of both. Figures 4 and 5 show the experimental results of a stainless steel plate sprayed with Lucyl type titanium oxide. In FIG. 4, “1” indicates the result before γ-ray irradiation, and “2” indicates the result after γ-ray irradiation for 10 days. It can be observed that the contact angle is reduced by the γ-ray irradiation. “3” indicates that the sample was left in a dark room for 2 weeks after γ-ray irradiation was cut off, indicating that the contact angle was closer to that before y-ray irradiation. After that, the re-irradiated y-rays are “4” and “5”. "5" has too good wettability, The contact angle could not be measured because the contact angle was less than 5 degrees. “6” was left in the dark room for 110 minutes from the state of “5”, indicating that the wettability was poor. In addition, in the “4”-“6” series compared to the “1”-“3” series, the test piece was placed near the γ-ray source. As shown in Fig. 5, the contact angle 0 changes (almost halved) 10 days after gamma irradiation. After this, the γ-rays are cut off again and the contact angle approaches that before y-ray irradiation when stored in a dark room (left in a dark room for 2 weeks). The experimental results for a titanium plate with an oxide film formed on the surface are shown in FIGS. 6 and 7. In FIG. 6, “1” indicates that the sample was irradiated with γ-rays for 10 days, and “2” indicates that the sample was irradiated with γ-rays for 10 days. It can be observed that the contact angle was reduced by the γ-ray irradiation. “3” indicates a case where the y-ray irradiation was cut off and left in a dark room for 110 minutes, and it can be seen that the contact angle approaches before the y-ray irradiation. As shown in Fig. 7, the contact angle before and after y-irradiation is about half to about one-tenth, depending on the dose.

With the installation of a number of experimental pieces, it was found that the change in wettability was caused more largely by the irradiation dose than by the wavelength and time of the y-ray. The change in contact angle decreases in inverse proportion to the distance from the source even when the gamma rays from the Co-60 source are received for the same time. To understand Lucille type that produced the wettability change physicochemical like situation oxide film titanium plate surface, the _three electron micrograph was observed with an electron microscope and X-ray diffraction, the surface of Lucille type titanium emission are The surface of the oxide film was found to be regularly arranged with particles with an average diameter of 7 to 8 m, while the particles were composed of relatively irregular particles of 20 to 30. X-ray diffraction can examine the composition from the surface to a depth of about 50 μm. It was found that the surface of the lucyl-type titanium is almost lucyl-type, but contains anatase-type titanium oxide. The composition of the surface of the oxide-coated titanium plate was almost entirely made of titanium, but the existence of a thin rusil-type oxide film was important. [Experiment 3]

A gamma irradiation experiment was performed at the Co-60 source experimental facility.

The following three test pieces were used.

(1) Titanium plate with oxide film formed on the surface (30 X 30 X 1 mm)

(2) Zircaloy plate (30 X 30 X 0.5 mm) with an oxide film on the surface

(3) Stainless steel plate with an oxide film on the surface (30 X 30 X 3 ram)

The oxide film is formed by irradiating high-temperature plasma to the metal surface and forming an oxide film on the metal surface by oxygen in the air.

The time-dependent change in wettability due to continuous gamma-ray irradiation was measured and compared with the titanium plate. The results are shown in FIGS. 8 and 9. Fig. 8 shows a comparison of three test pieces before and after irradiation with y / ray for 90 hours. FIG. 9 is a graph showing changes in contact angle due to γ-ray irradiation. In the figure, solid lines, broken lines, and dashed lines indicate changes in a titanium plate, a zircaloy plate, and a stainless steel plate, respectively. In the figure, no significant improvement in the wettability was observed for the stainless steel sheet, but for the Zircaloy sheet, similar to the titanium plate, the improvement in the wettability was observed with the change in the irradiation time. This is probably because an oxide film similar to titanium metal was formed on the surface. The longer the continuous irradiation time, the more the wettability is improved, and if the irradiation time is further extended, it is expected that a super-lyophilic state will be obtained.

Β. Relationship between critical heat flux and γ-ray dose

Figure 10 shows the boiling characteristic curve. The characteristics of boiling heat transfer can be expressed by the difference between the ripening flux of the heat transfer surface, the temperature of the heat transfer surface, and the saturation temperature of the liquid. In the figure, the area between A Β is the natural convection region of a non-boiling liquid single phase, the point B is the boiling start point, the area between BD is nucleate boiling, D is the maximum heat flux point (critical heat flux), and DE is the transition. Boiling, E is the minimum heat flux point, and exceeding E results in film boiling. For example, in a nuclear reactor, the fuel rod surface temperature is higher than the boiling temperature If it is not high, it is nucleate boiling, and if it is sufficiently high, it becomes a film boiling. In general, the heat flux is small when the difference between the fuel rod and the saturation temperature of water is small, but when the temperature of the fuel rod increases and the temperature difference increases, the heat flux increases due to nucleate boiling. In the intermediate region between nucleate boiling and film boiling, a considerable portion of the fuel rod surface becomes covered with steam, heat transfer becomes unstable, and the heat flux decreases as the temperature difference increases. . For heat transfer phenomena due to phase changes such as boiling and condensation, it is ultimately necessary that the material and the liquid be in contact. This is because the thermal conductivity of vapor or gas is remarkably low, typically about 100,000 for liquid, and the vapor phase covering the member surface impedes heat transfer. In the nucleate boiling region, the heat transfer coefficient is improved due to the movement caused by vigorous boiling bubble generation as the heat transfer surface temperature increases. However, on the other hand, the amount of boiling bubbles generated also increases, and the action of the vapor bubbles covering the heat transfer surface occurs. Eventually, the vapor bubbles cover the entire heat transfer surface, causing a rapid decrease in heat transfer coefficient (boiling transition). Therefore, it would be advantageous if the maximum heat flux point (critical heat flux) could be increased.

[Experiment 4]

The critical heat flux was measured using the experimental device shown in Fig. 11. Heat flux (W / m ²⁾ is due Ri is calculated on the surface area of the power consumption (W) and a test piece obtained from the voltage and circuit current of the test pieces (m ^2). The critical heat flux is the heat flux when the test piece breaks. Such experimental devices and methods are well known. The test pieces were rod-shaped titanium oxide and rod-shaped titanium (an oxide film was formed on the surface). Fig. 12 shows the experimental results, and it can be seen that as the γ-ray irradiation amount increases, the critical heat flux also increases.

C. Leidenfrost phenomenon Figure 13 shows the life of a water drop on a hot surface. When a droplet of a certain size is dropped on a hot surface and the time until evaporation is measured, the evaporation time (droplet life) decreases rapidly with the temperature of the hot surface at the beginning. Eventually, the temperature gradually decreases from the minimum value (the maximum point of the evaporation time from the viewpoint of a short evaporation time) to the maximum value, and then gradually decreases again with the temperature. On the hot side from the maximum point of the evaporation time, a vapor film is formed between the droplet and the hot surface. The phenomenon in which droplets are separated from the surface by the vapor film and do not wet the surface as a result is called Leidenfrost phenomenon. The lower limit of the Leidenfrost phenomenon, that is, the maximum point of the evaporation time, is called the Leidenfrost point.

[Experiment 5]

The surface of titanium is irradiated with high-temperature plasma, and a test piece having an oxide film formed on the surface of titanium is irradiated with γ-rays (800 kGy) by oxygen in the air, and treated with γ-rays. It was compared with the test piece without. The experiment was performed at 235 ° C, 240, and 260 ° C. C, 280. C, 300. C, 320 ° C, 340. The same was done at 7 points. As shown in Fig. 14, droplets were dropped on the surface of a rectangular test piece using a micro syringe and observed visually. The left test piece was not gamma-ray treated, and the right test piece was gamma-ray treated. Since the surface of the test piece is not concave, if it does not evaporate, the droplet rolls on the test piece surface and comes off the test piece surface. Figure 15 shows the results. In the figure, 〇 means that the droplet was rolled off the test piece while remaining spherical. X and △ indicate that the droplet was instantaneously evaporated. The mouth does not mean that the droplet evaporates instantaneously, but shows a case where the droplet is decomposed and evaporated while forming a smaller spherical droplet. From this result, it can be seen that the Leidenfrost point shifts to the higher temperature side by irradiation with y-rays. That is, irradiate y-rays This shows that the wettability can be improved even in a high temperature range from 230 ° to 300 °. Industrial applicability

INDUSTRIAL APPLICABILITY The present invention can be used for improving a heat transfer mechanism in a radiation environment such as a nuclear reactor and a spacecraft. INDUSTRIAL APPLICABILITY The present invention is applied to the improvement of a heat transfer mechanism by simultaneously providing a radiation environment even in a normal radiation environment. INDUSTRIAL APPLICABILITY The present invention is used for improving a mechanism that requires wettability such as lubrication and chemisorption in a normal radiation environment or when a radiation environment is simultaneously applied.

Claims

The scope of the claims

I. A method for improving wettability, comprising disposing a substrate having a catalyst layer on the surface thereof in a radiation environment to improve the wettability of the surface.

2. The method for improving wettability according to claim 1, wherein the surface of the substrate is irradiated with radiation to improve the wettability of the surface.

3. The method for improving wettability according to claim 1, wherein the radiation is selected from α rays, 0 rays, y rays, X rays, and neutron rays.

4. The method for improving wettability according to claim 1, wherein the catalyst layer is titanium oxide.

5. The method for improving wettability according to claim 4, wherein the titanium oxide is a lusyl-type titanium oxide.

6. The method for improving wettability according to claim 1, wherein the catalyst layer is an oxide film formed on the surface of the substrate.

7. The method for improving wettability according to claim 6, wherein the substrate is a metal, and the catalyst layer is an oxide film of the metal.

8. The method for improving wettability according to claim 7, wherein the metal is selected from stainless steel, Zircaloy, and titanium.

9. A method for improving wettability, comprising disposing a member having a surface formed with a film of rutile-type titanium oxide in a y-ray environment to improve the wettability of the surface.

10. A method for improving wettability, comprising disposing a member having an oxide film formed on a surface thereof in a gamma ray environment to improve the wettability of the surface.

I I. The method for improving wettability according to claim 10, wherein the base material is a metal, and the oxide film is an oxide of the metal.

12. The method according to claim 11, wherein the metal is selected from stainless steel, Zircaloy, and titanium.

1 3. A member whose surface is coated with a Lucyl-type titanium oxide film and is always placed under the gamma-ray environment.

1 4. In claim 13, the member is a member constituting a nuclear reactor.

1 5. In claim 14, the member is a member constituting a core.

1 6. In claim 15, the member is a member constituting a fuel assembly.

17 In claim 16, the member is a fuel rod.

18 In claim 14, the member is a reactor vessel having a reactor core therein.

1 9. In claim 14, the member is a containment vessel of a nuclear reactor. 20. A member that has an oxide film formed on its surface and is always placed in a gamma-ray environment.

2 1. In Claim 20, the member is a member constituting a nuclear reactor. 2 2. In Claim 21, the member is a member constituting a core. 23. In Claim 22, the member is a member constituting a fuel assembly.

24 In claim 23, the member is a fuel rod.

25 In claim 20, the member is a reactor vessel having a reactor core therein.

26 In claim 20, the member is a containment vessel of a nuclear reactor. 27 A method for improving heat transfer, characterized by improving the efficiency of heat transfer from the fuel rods to the coolant by providing a film of rutile titanium oxide on the surface of the fuel rods of the nuclear reactor.

2 8. A method for improving heat transfer characterized by improving the efficiency of heat transfer from the fuel rods to the coolant by forming an oxide film on the surface of the fuel rods of the reactor 2 9. Claims 2 8, the oxide film may be made of titanium or zircon. A method for improving heat transfer, characterized in that it is an oxide film of force roy.

30. Fuel rods with a sulcil-type titanium oxide coating on the outer surface.

3 1. Fuel rods with an oxide film formed on the outer surface.

32. The fuel rod according to claim 31, wherein the oxide film is a zircaloy oxide film.

3 3. A nuclear reactor vessel characterized in that a rusil type titanium oxide film is formed on the wall.

3 4. Reactor vessel characterized by having an oxide film formed on the wall.

3. Reactor containment vessel characterized in that the wall is coated with a Lucyl-type titanium oxide film.

3 6 · A containment vessel characterized by having an oxide film formed on the wall.