JP2863939B2 - Tritium permeation reduction device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for handling tritium, a device for holding tritium, and a device for reducing permeation of tritium diffused and transmitted from a pipe.

[Conventional technology]

A sodium-cooled fast breeder reactor will be described as an example of an apparatus for handling trichiune. In a sodium-cooled fast breeder reactor, tritium, a radioisotope of hydrogen having a mass number of 3, is generated by three-body fission of nuclear fuel, diffused and transmitted through a nuclear fuel cladding tube, and released into a coolant. Most of the tritium in the coolant is removed by cooling to 120 to 150 ° C. with an impurity removing device called a cold trap for precipitating and removing impurities such as oxides and hydrides in the coolant. However, since the equipment and piping that make up the reactor cooling system are made of stainless steel, which allows tritium to diffuse and permeate easily, some tritium in the coolant diffuses and permeates from the equipment and piping and is released to the outside. Performing maintenance work on the apparatus so as not to be affected as much as possible has caused a reduction in work efficiency. As a method for reducing the amount of tritium in a coolant discharged from equipment and piping, JP-A-51-27808 discloses a method in which a cooling pipe or a cooling jacket is provided in the cold trap, and tritium diffused and transmitted from the coolant is disclosed. A technique is described in which the liquid is guided to a tritium recovery device connected to a cooling pipe or a cooling jacket for recovery.

FIG. 8 shows an example in which a cooling pipe is provided in a cold trap to recover tritium. Tritium in the coolant 14 flowing into the cold trap 2 from the coolant inflow pipe 1 precipitates on the outer surface of the cooling pipe 3. The deposited tritium is diffused and transmitted through the cooling pipe 3 and is mixed with an inert gas circulating in the cooling pipe 3. The mixed tritium is mixed with the inert gas together with the cooling pipe 3.
Is introduced into the nickel thin film 5 from the outlet nozzle 4 and only tritium is diffused and permeated and collected in the vessel 6, oxidized in the catalyst tower 7 to become water, and sent to the outside of the system through the drain port 8.

FIG. 9 shows a device for collecting tritium which diffuses through the cooling pipe 3 shown in FIG. 8 and is mixed with the inert gas circulating in the cooling pipe 3, and a cooling jacket provided in a cold trap to collect tritium. An example is shown below. This is an example in which a cooling jacket 15 is provided in the cold trap 2 and a device for circulating an inert gas therein and collecting tritium mixed therein is provided.

[Problems to be solved by the invention]

Although the above prior art is capable of recovering tritium from the coolant of the reactor cooling system, a device for recovering tritium, that is, a pipe extending from the outlet nozzle 4 of the cooling pipe 3 of the cold trap 2 to the nickel thin film 5, Cooling jacket
No consideration was given to re-emission from the surface of No. 15, and if a tritium recovery device was installed to prevent re-emission, the equipment would be large-scale, and the tritium recovery efficiency could not be said to be high, and there was also an economic problem. .

Further, the diffusion and transmission of tritium from equipment and piping follow Fick's law, which is proportional to the product of the diffusion coefficient in equipment and piping material and the concentration of tritium in the coolant, but is completely cooled by the cold trap 2 of the prior art. Tritium in the material is not removed, the tritium concentration is at the saturation concentration at the temperature of the cold trap 2,
Some diffusion and transmission from the equipment and piping of the reactor cooling system containing tritium is inevitable. At present, no device for suppressing the diffusion and transmission from them has been studied.

An object of the present invention is to solve the problems of the prior art and to suppress the diffusion and transmission of tritium from a device that handles tritium.

[Means for solving the problem]

The above object is achieved by providing a thorium permeation reduction device in which an oxide film is formed on at least the surface of a device containing tritium.

The above object is achieved by providing a tritium permeation reduction device in which an oxide film is formed on the surface of a jacket provided on the outside.

The above object is achieved by providing a tritium permeation reduction device having an oxide film formed on the surface of a heat insulating material cover of the device.

[Action]

According to the above configuration, the diffusion transmission of tritium from the equipment and the pipe follows Fick's law that is proportional to the product of the diffusion coefficient in the equipment and the pipe material and the tritium concentration in the coolant, By forming an oxide film, the oxide film physically fills the gaps between the crystals, and chemically reacts with oxygen and tritium in the oxide film to form large molecules, which reduces the diffusion coefficient and reduces the diffusion and transmission of tritium. .

〔Example〕

 Embodiments of the present invention will be described with reference to the drawings and tables.

First Embodiment The first embodiment is an example in which an oxide film is formed on the outer surface of a device containing tritium. First, the overall configuration will be described.

FIG. 1a is a longitudinal sectional view of the cold trap 2 for collecting tritium in the coolant, and FIG. 1b is an enlarged view of a portion A thereof. In FIG. 1a, a mesh 13 made of a non-homogeneous substance is provided in a cold trap 2, a cylindrical heat insulating plate 21 fixed to the outer periphery thereof, a cold trap 2 and a heat insulating plate 21.
And a cooling pipe 3 arranged in a spiral shape.
The coolant inlet pipe 1 and the coolant outlet pipe 12 are connected to the top of the cold trap 2, and form an oxide film 17 on the outer surface of stainless steel SUS304 or CrMo steel constituting the body of the cold trap 2. .

 Next, the operation will be described.

When the coolant 14 containing tritium mixed into the cold trap 2 from the coolant inflow pipe 1 descends outside the heat insulating plate 21, the coolant 14 is cooled to 120 to 150 ° C. by the cooling pipe 3. The mesh 13 in the plate 21 rises and flows out of the cold trap 2 from the coolant outflow pipe 12. At this time, most of the tritium in the coolant 14 becomes supersaturated with hydrogen as an isotope and precipitates on the mesh 13, but a part also precipitates on the inner surface of the cold trap 2 and the surface of the cooling pipe 3. Tritium deposited on the inner surface of the cold trap 2 diffuses through the material at a diffusion rate determined by the temperature, and the oxide film 17
, But here the diffusion rate of tritium is greatly reduced, so that the amount of permeation is reduced. As a result, tritium transmitted from the cold trap 2 is reduced.

In this embodiment, it is conceivable to form an oxide film on the inner surface of the cold trap 2, but it is possible if there is no corrosion by sodium of the coolant.

Second Embodiment A second embodiment is an example in which an oxide film is formed on the outer surface of a pipe containing tritium.

FIG. 2 shows a longitudinal section of a pipe 20 having a coolant 14 mixed with tritium and having an oxide film 17 formed on the outer surface.

When the coolant 14 flows through the pipe 20, a boundary layer is generated near the inner surface of the pipe 20 due to the viscosity of the coolant 14. Coolant 14
The tritium inside diffuses through the boundary layer and adheres to the inner surface, diffuses through the pipe 20, and most of the tritium is retained by the oxide film 17. Therefore, the diffusion and transmission through the pipe 20
The amount of tritium released to the outside is reduced.

Third Embodiment A third embodiment is an example in which an oxide film is formed on an inner surface and an outer surface of a jacket member or a heat insulating material cover provided on a device holding tritium.

FIG. 3a is a longitudinal sectional view of the cold trap 2 provided with the cooling jacket 15. FIG.

FIG. 3b is an enlarged sectional view of the cooling jacket 15B, in which an oxide film 17 is formed on the inner surface and the outer surface of the cooling jacket 15.

FIG. 4a is a longitudinal sectional view of the cold trap 2 which has been kept warm.

FIG. 4b is an enlarged sectional view of a portion C of the heat insulating material cover 19, in which an oxide film 17 is formed on the inner surface and the outer surface of the heat insulating material cover 19.

In the case of this embodiment, since the oxide film 17 is formed at a plurality of places, the effect of reducing the amount of released tritium is higher than in the first and second embodiments.

Fourth Embodiment The fourth embodiment is an example in which an oxide film is formed on the outer surface of a pipe held by tritium lithium, and an outer pipe or heat insulation is further provided outside the oxide film.

FIG. 5 is a longitudinal sectional view in which a pipe 20 having an oxide film 17 formed on the outer surface is inserted into the pipe 20 having the oxide film 17 formed on both sides of the inner surface and the outer surface to form a double pipe.

In FIG. 6, the outside of the pipe 20 having the oxide film 17 formed on the outer surface is covered with a heat insulating material 18, and the outside thereof is further covered with the heat insulating material cover 19 having the oxide film 17 formed on both the inner surface and the outer surface. It is a longitudinal cross-sectional view in the case.

In the case of this embodiment, since the oxide film 17 is formed at a plurality of locations, the effect of reducing the amount of tritium released from the pipe is higher than in the second embodiment.

When an oxide film is formed on the surface of equipment and piping containing tritium to a thickness of about 5 μm, the diffusion coefficient of tritium is reduced to less than one-hundredth in the case of stainless steel as shown in FIG. As is clear from the figure, the diffusion coefficient increases as the temperature of the material increases, so that the diffusion and transmission of tritium does not increase if the thickness of the oxide film at the place where the surface temperature of the equipment and piping is high is increased.

A method for forming an oxide film on the surfaces of equipment and piping containing tritium will be described.

In the first method, iron and water vapor in the material are reacted at a high temperature according to the following equation.

3Fe + 4H ₂ O → Fe ₃ O ₄ + 4H _{2 In} the second method, iron in the material is subjected to a chemical conversion treatment with a high-temperature aqueous sodium hydroxide solution.

By the above method, a film of a magnetite layer having a thickness of about 5 μm made of ferric oxide is formed.

As described above, in the embodiment, the sodium-cooled fast breeder reactor has been described as an example. However, the present invention is not limited to this device, and the same effect can be obtained in other devices handling tritium, for example, a nuclear fuel reprocessing device. Is obtained.

〔The invention's effect〕

According to the present invention, the diffusion coefficient of tritium is reduced and the amount of diffusion permeation is reduced by forming an oxide film on the surface of equipment and piping material containing tritium of the apparatus, so that the efficiency of maintenance work of the apparatus is reduced. The effect of improving is obtained.

[Brief description of the drawings]

1a is a longitudinal sectional view of a cold trap according to an embodiment of the present invention, FIG. 1b is a partially enlarged view of FIG. 1a, FIG. 2 is a longitudinal sectional view of a pipe in an embodiment of the present invention, and FIG. FIG. 3b is a partial enlarged view of the cold trap provided with the cooling jacket in the embodiment of the invention, FIG. 3b is a partially enlarged view of FIG. 3a, FIG. 4b is a partially enlarged cross-sectional view of FIG. 4a, FIG. 5 is a longitudinal cross-sectional view in the case where a pipe having an oxide film formed on the surface thereof in the embodiment of the present invention is a double pipe, and FIG. 6 is an embodiment of the present invention. FIG. 7 is a longitudinal sectional view showing the case where the outside of the pipe in the example is covered with a heat insulating material cover formed with an oxide film on both sides, FIG. 7 is a table showing the effect of the oxide film in the embodiment of the present invention, and FIG. FIG. 9 is a system diagram of a cold trap and a tritium recovery device, and FIG. It is a system diagram of Dotorappu and tritium recovery device. DESCRIPTION OF SYMBOLS 1 ... Coolant inflow pipe, 2 ... Cold trap, 3 ... Cooling pipe, 4 ... Outlet nozzle, 11 ... Inlet nozzle, 12 ... Coolant outflow pipe, 13 ... Mesh, 14 ... Coolant, 15 ... Cooling jacket,
17… Oxide film, 18… Heat insulator, 19… Heat insulator cover, 20… Piping, 21… Insulation board

Continuing from the front page (72) Inventor Hiroyuki Handa 3-2-1 Sachimachi, Hitachi City, Ibaraki Prefecture Within Hitachi Engineering Co., Ltd. (72) Inventor Hiroyuki Imabashi 3-2-1 Sachimachi, Hitachi City, Ibaraki Prefecture Hitachi Engineering Co., Ltd. In company

Claims (3)

(57) [Claims] 1. An apparatus for reducing permeation of tritium, wherein an oxide film is formed on at least the surface of the apparatus containing tritium. 2. The apparatus for reducing permeation of tritium according to claim 1, wherein an oxide film is formed on a surface of a jacket provided outside the apparatus. 3. The apparatus for reducing permeation of tritium according to claim 1, wherein an oxide film is formed on a surface of a heat insulating material cover of said apparatus.