JPH10204666A - Reactor fuel rod and its corrosion preventive method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the corrosion preventive effects of many fuel rod containers uniform and to decrease the labor of corrosion preventive work by forming coating layers consisting of TiO2 on the surfaces of these fuel rod containers, thereby improving the corrosion preventives of the fuel rod containers as the time of executing corrosion prevention by utilizing photo-electrode reaction. SOLUTION: The fuel rod 2 has a structure obtd. by housing plural pellets P in a stacked state into a fuel clad pipe 3a of the fuel rod container 3, fixing these pellets by utilizing the repulsive force of repulsive members 6, such as coil springs, closing the upper and lower openings of the fuel clad pipe 3a with caps and hermetically sealing the caps by welding. Further, the fuel rod container 3 is formed of zircaloy (zirconium alloy) and is formed with the coating layer 7 consisting of TiO2 so as to cover the entire surface. As a result, the corrosion preventive effects of the fuel rod containers 3 are made additionally higher. The corrosion preventive effects are evenly applied to the entire area of the fuel rod containers by utilizing the photo-electrode reaction by radiations and Cerenkov light, by which the quality of the fuel rod containers 3 is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel rod for a nuclear reactor and a method for preventing corrosion thereof, and more particularly to a technique for preventing corrosion using a photoelectrode reaction.

[0002]

2. Description of the Related Art In a light water reactor using water as a coolant, most of the internal structure of a reactor pressure vessel surrounding a reactor core includes:
Since it is placed in high-temperature reactor cooling water and used in the atmosphere of radiation emitted from the reactor core, its constituent materials have corrosion resistance to reactor cooling water, and must not be affected by water decomposition of radiation. Special attention is paid to quality control, such as consideration.

[0003] In a fuel container containing a reactor fuel, zircaloy (zirconium alloy) having excellent corrosion resistance in high-temperature pure water is used.

On the other hand, even Zircaloy is exposed to a strong radiation atmosphere for a long period of time, undergoes repeated thermal cycling, and after being extracted from a nuclear reactor, for example, as spent fuel in a fuel pool water. Therefore, it is necessary to monitor the degree of corrosion.

[0005] Examples of a method for producing a titanium oxide film for corrosion protection and a technique related to the titanium oxide film for corrosion protection are described in Japanese Patent Application Laid-Open No. 07-270592, entitled "Reactor Fuel Material and Corrosion Protection Method". Techniques relating to a method for manufacturing a titanium oxide film used for an internal structure have been proposed. This technology utilizes the semiconductor characteristics of a titanium oxide film made of titanium oxide or the like, and causes a non-consumable anode reaction when irradiated with radiation or Cherenkov radiant light, thereby producing a titanium oxide film (semiconductor film). The corrosion potential on the surface of the nearby reactor structural material is lowered to prevent metal corrosion.

The above publication discloses that TiO ₂ is sprayed on the surface of a structural material by spraying Ti in an atmosphere containing oxygen.
Are described.

[0007]

However, in a nuclear fuel assembly, since a plurality of fuel rod containers made of Zircaloy are assembled, a narrow portion is formed between the fuel rod containers. Therefore, even if a titanium oxide film is formed on a structural material near the nuclear fuel assembly, it cannot be said that the anticorrosion effect is narrow and extends to the fuel rod container at the portion.

[0008] The present invention has been made in view of such problems, and has the following objects. Improve the corrosion protection of fuel rod containers. Equalize the anticorrosion effect of many fuel rod containers and stabilize the quality. To reduce the labor of anticorrosion treatment work. Improve anticorrosion of stored spent fuel in a fuel pool.

[0009]

Means for Solving the Problems The surface of the fuel rod container is made of Ti.
A technique for improving the fuel rod corrosion prevention effect by forming a coating layer made of O ₂ is employed. In this case, a coating layer made of TiO ₂ is formed on the surface of the fuel rod container, and a photoelectrode reaction based on radiation or Cerenkov light generated from the fuel rod during operation of the reactor or after operation causes the fuel container and its vicinity to be exposed. A technology for preventing corrosion of a welding portion or the like is employed. In the coating layer of the fuel rod container, a technique of forming a titanium oxide film on the surface of the fuel rod container in advance by the method described in the above-mentioned technical example: Japanese Patent Application Laid-Open No. 07-270592, or a method of depositing TiO ₂
The solution is brought into contact with the surface of the fuel rod container technique to deposit TiO ₂ is employed.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a fuel rod for a nuclear reactor and a method for preventing corrosion according to the present invention will be described below with reference to FIGS.

1 to 3, reference numerals 1A and 1B denote a fuel assembly, 2 denotes a fuel rod, 3 denotes a fuel rod container, 4 denotes a channel box, 5 denotes a support grid, 6 denotes a resilient member, 7
Is a coating layer, P is a pellet, and W is a weld.

FIG. 1 shows a fuel assembly 1 for a boiling water reactor.
A is shown in FIG. 2, and a fuel assembly 1B for a pressurized water reactor is shown.
Is shown. The fuel assembly 1A of FIG. 1 has a structure in which a plurality of fuel rods 2 are fixed by a channel box 4, and the fuel assembly 1B of FIG.
This is a structure in which a plurality are fixed.

The fuel rod 2 stores a plurality of pellets P in a stacked state in a fuel cladding tube 3a of a fuel rod container 3, and utilizes the resilience of a resilient member 6 such as a coil spring. The upper and lower openings of the fuel cladding tube 3a are closed with lids, and the fuel cladding tube 3a is sealed with a welded portion W.

Further, in the fuel rod container 3, in addition to being formed from zircaloy (zirconium alloy), a coating layer 7 made of TiO ₂ is formed on the entire surface to cover the entire surface. I have.

Before the pellets P are loaded into the fuel rod container 3, the coating layer 7 has at least a fuel cladding tube 3a.
A titanium oxide film (TiO ₂ ) is formed on the surface according to, for example, the above-mentioned technical example.

[0016] The coating layer 7 consisting of TiO ₂ as another method for forming the surface of the fuel rod container 3, utilizing the Ti solution having a function of attaching the TiO ₂ crystallized precipitates of TiO ₂ on the surface Can be. As the Ti solution, for example, a solution obtained by diluting Ti propoxide with pure water can be used. When the Ti solution is brought into contact with the fuel rod container 3, the method may be such that the Ti solution is brought into contact with the fuel cladding tube 3 a, after the pellets P are stored, or the fuel assembly (1).
A, is a method adopted to contact in the state of 1B), as desirably high temperature and high pressure atmosphere surrounding environment, techniques to accelerate the separation of TiO _2, thereby the TiO ₂ crystallized attached to the surface of the fuel rod container 3 Is adopted.

When the coating layer 7 made of TiO ₂ is formed on the surface of the fuel rod container 3, the photoelectrode reaction (non-consumable anode reaction) by receiving radiation or Cherenkov light generated during the operation of the reactor. And fuel rod container 3
The anticorrosion effect is obtained by lowering the corrosion potential on the surface of.

In this case, radiation and Cherenkov light are reflected on the surface of the reactor structure and spread to various parts. Therefore, even in a narrow part, the anticorrosion effect is sufficiently provided even in a part where the coating layer 7 is formed. Demonstrate. Above all, the fuel rod container 3 for storing the pellets P as the fuel is a portion that is most strongly affected by the radiation and the Cherenkov light, so that the anticorrosion effect can be exhibited most effectively.

FIG. 4 shows the transition of the intensity of the radiated light generated from the spent fuel over time. Light intensity (number of photons) in both high-burning spent fuel (high burnup) with a high degree of combustion due to long-term use, etc. and spent fuel (low burnup) with a relatively low degree of combustion Although there is a difference in the level of
It is clear that radiation and Cherenkov light have been generated from the spent fuel for a long period of time after the lapse of 00 days and 3600 days, and it is possible to perform anticorrosion using the photoelectrode reaction in the coating layer 7.

Therefore, in both the case where the fuel rods 2 are operating inside the nuclear reactor and the case where the fuel rods 2 are stored in the fuel pool as spent fuel, the coating layer is formed in an atmosphere where water is interposed. In the vicinity of the TiO ₂ film of No. 7, anticorrosion utilizing photoelectrode reaction can be performed. For example, even if the coating layer 7 is formed only on the cylindrical surface of the fuel cladding tube 3a, not only the welding portion W but also the anticorrosion effect is obtained. And further enhances the anticorrosion effect in addition to the corrosion resistance of Zircaloy.

[0021]

According to the nuclear reactor fuel rod and the method for preventing corrosion of the nuclear reactor according to the present invention, the following effects can be obtained. (1) By forming a coating layer made of TiO _{2 on} the surface of Zircaloy having excellent corrosion resistance, the corrosion prevention effect of the fuel rod container can be further enhanced. (2) By forming a coating layer made of TiO _{2 on} the surface of the fuel rod container, an anticorrosion effect is uniformly imparted to the entire area of the fuel rod container by utilizing a photoelectrode reaction caused by radiation or Cherenkov light. Quality can be stabilized. (3) By mixing the processing liquid composed of the TiO ₂ raw material into the reactor cooling water and attaching TiO ₂ to the surface of the fuel rod container, the labor of the anticorrosion processing operation can be reduced. (4) Ti of radiation or Cherenkov light with long irradiation life
By utilizing the photoelectrode reaction to O _2, the anticorrosion of the spent fuel during storage in a fuel pool or the like can be improved.

[Brief description of the drawings]

1A is a front view of a fuel assembly for a boiling water reactor, and FIG. 1B is a partially cutaway front view showing a fuel rod thereof.

FIG. 2A is a front view of a fuel assembly for a pressurized water reactor, and FIG. 2B is a partially cutaway front view showing a fuel rod thereof.

FIG. 3 is a partially cutaway front view showing one embodiment of the reactor fuel rod according to the present invention.

FIG. 4 is a diagram showing a temporal change of emitted light in a spent fuel.

[Explanation of symbols]

 Reference Signs List 1A fuel assembly 1B fuel assembly 2 fuel rod 3 fuel rod container 3a fuel cladding tube 4 channel box 5 support grid 6 resilient member 7 coating layer P pellet W welded part

Claims (4)

[Claims] 1. A nuclear reactor fuel rod comprising a coating layer (7) made of TiO _{2 on} the surface of a fuel rod container (3). 2. A fuel rod container (3) having a coating layer (7) made of TiO ₂ formed on a surface thereof, and a photoelectrode reaction based on radiation or Cherenkov light generated from the fuel rod (2). A method for preventing corrosion of nuclear fuel rods, comprising preventing corrosion of fuel. 3. The corrosion prevention of a nuclear fuel rod according to claim ₂ , wherein a coating layer made of TiO ₂ is formed on the surface of the fuel rod container by contacting the Ti solution. Method. 4. The method according to claim 2, wherein a coating layer (7) is formed on the surface of the fuel rod container (3) to prevent corrosion of a welded portion or the like in the vicinity thereof.