JPH05288942A - Production of radiation resistant image fiber - Google Patents

Abstract

PURPOSE:To improve radiation resistance by subjecting an image fiber base material to melt spinning and irradiating the resulted image fiber with gamma rays, then heating the fiber in a hydrogen atmosphere. CONSTITUTION:The end of the image fiber base material 11 is melted by a heater 12 of a heating furnace and is melt spun, by which the image fiber 13 having a desired diameter is formed. This image fiber 13 is continuously introduced to a resin coating die 14 filled with a heat resistant UV curing type resin liquid and is coated with the resin liquid; thereafter, the fiber is sent to a UV crosslinking cylinder 15 where the fiber is irradiated with UV rays. As a result, the resin liquid is cured and the resin coating is applied. The image fiber 13 provided with such resin coating is in succession sent continuously to an irradiation chamber 16. A gamma ray source 17 for cobalt 60, etc., is installed in this chamber. The image fiber 13 is subjected to the irradiation with the rays during traveling in the irradiation chamber 16 and is then heated and treated in a hydrogen atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a radiation resistant image fiber having significantly improved radiation resistance.

[0002]

2. Description of the Related Art As an application of an image fiber, it is used in a radiation environment such as an inspection of a cooling water pipe in a nuclear power plant. As an image fiber used for such an application, it is naturally necessary to use an image fiber whose transmission characteristics are minimally deteriorated even when exposed to radiation. 2. Description of the Related Art Conventionally, as a radiation resistant image fiber used in such a radiation environment, as shown in FIG. 2, a large number of cores 1 made of pure quartz glass and fluorine-doped quartz surrounding the cores 1 ... It is known to have a clad 2 made of glass and a jacket 3 made of quartz glass that covers the whole of the clad 2.

Such an image fiber is a pipe made of pure silica glass, which serves as a jacket by bundling a plurality of optical fibers having a core / grad structure having a core made of pure silica glass and struts made of fluorine-doped silica glass in an aligned state. It is manufactured by a method in which the image fiber base material is housed in the inside, heated to form an integrated image fiber base material, and the image fiber base material is melt-spun. However, during this melt spinning, a defect occurs in the image fiber, and the defect remains in the obtained image fiber. This defect changes to a color center (coloring center) when exposed to radiation, which causes deterioration of transmission characteristics.

Therefore, in order to remove the defects existing in the image fiber, a method of heating the image fiber in a hydrogen atmosphere has been adopted, and the defects have been removed in advance to enhance the radiation resistance. However, even if this method is used, the radiation resistance of the image fiber is still insufficient, and the transmission characteristics are deteriorated even when exposed to a high dose.

[0005]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to obtain a method of manufacturing an image fiber having extremely excellent radiation resistance without deterioration of transmission characteristics even when exposed to a high dose of radiation. ..

[0006]

This problem is solved by a method of irradiating the image fiber after melt spinning with γ-rays and then heating it in a hydrogen atmosphere. Irradiation with γ-rays may be carried out continuously (tandem) following melt spinning, or may be a method of once winding after melt spinning and irradiating.

The present invention will be described in detail below. Figure 1
Shows an apparatus suitable for carrying out an example of the manufacturing method of the present invention. Reference numeral 11 in FIG. 1 denotes an image fiber preform. The image fiber base material 11 is not particularly limited, but from the viewpoint of radiation resistance, a core / glad type light having a core made of pure quartz and a glad made of fluorine-doped quartz glass or boron-doped quartz glass. It is preferable that a large number of fibers are bundled in an aligned state, housed in a pipe made of quartz glass, heated, and integrated. The end portion of the image fiber base material 11 is melted by a heater 12 of a heating furnace and melt-spun to form an image fiber 13 having a desired diameter.

The image fiber 13 is continuously guided to a resin-coated die 14 filled with a heat-resistant ultraviolet-curable resin liquid, coated with the resin liquid, and then sent to an ultraviolet cross-linking cylinder 15, where Receives UV irradiation. As a result, the resin liquid is hardened and a resin coating is applied. The image fiber 13 provided with this resin coating is continuously sent to the irradiation chamber 16 continuously. The irradiation chamber 16 is for irradiating the image fiber 13 running in the irradiation chamber with γ-rays, and a γ-ray source 17 such as cobalt-60 is installed inside thereof.

The image fiber 13 is provided in the irradiation chamber 16
Γ of dose of about 10 ⁷ to 10 ⁹ roentgen while traveling inside
After receiving the line irradiation, it is wound around the winding drum 18.
The traveling linear velocity of the image fiber 13 is usually 10 to 100 m
Since it is about / min, it is preferable that the γ-ray source can irradiate γ-rays at a relatively high dose rate, and when Cobalt-60 is used, a source of about 10 ¹⁰ curies is used.

The wound image fiber 13 is then heated and processed in a hydrogen atmosphere. This process is
Image fiber 1 wound in a heat-resistant pressure vessel 1
3 is accommodated, the container is filled with hydrogen gas, and the image fiber in the container is heated. The hydrogen gas used here may be a mixed gas of hydrogen gas and an inert gas such as argon gas or nitrogen gas other than pure hydrogen gas. By this treatment, hydrogen atoms permeate and diffuse into the glass forming the image fiber to cure the defect. At this time, the resin coating does not hinder the permeation of hydrogen molecules at all, and since it is in a crosslinked state, it is hardly deteriorated by heating.

According to such a manufacturing method, by irradiating the image fiber 13 after melt spinning with γ-rays, many defects are positively generated in the image fiber 13, and these defects are generated by hydrogen in the next step. Since it is removed by the treatment, extremely high radiation resistance can be obtained. Further, when the radiation dose received during service is predicted in advance, the radiation dose at the time of γ-ray irradiation can be made to correspond to this, and efficient processing can be performed. Furthermore, in the manufacturing method of this example, γ
Since the linear irradiation is continuously performed in tandem following the melt spinning, the working time can be shortened and the manufacturing cost can be reduced.

Further, in the manufacturing method of the present invention, the γ-ray irradiation does not necessarily have to be performed by melt spinning and tandem, and the image fiber coated with the resin is once wound on the winding drum,
The wound image fiber may be irradiated with γ-rays in an irradiation chamber and then heat-treated in a hydrogen atmosphere. Alternatively, a method may be employed in which the image fiber after winding is heated in advance in a hydrogen atmosphere to remove defects generated during melt-spinning, then subjected to γ-ray irradiation, and then heated again in a hydrogen atmosphere. .. In these methods, a relatively small low dose rate γ-ray source can be used for γ-ray irradiation, which is advantageous in terms of management of equipment and radiation equipment.

Hereinafter, the present invention will be specifically described with reference to examples. (Example 1) An image fiber preform was melt-spun to obtain an image fiber having an outer diameter of 1.5 mm. In this image fiber, the core is made of pure silica glass, the glad is made of fluorine-doped silica glass, and the core diameter is 6.
5 μm, core interval is 10 μm, Δn 1.0%, and the number of pixels is 30.000. In this image fiber,
Immediately after spinning, an ultraviolet curable resin was applied and cured with an ultraviolet crosslinking cylinder to provide a coating having a thickness of 150 μm. This product was immediately and continuously introduced into the irradiation chamber for γ-ray irradiation. As the γ-ray source, 10 ⁸ Ci cobalt-60 was used.

Then, after winding this on a winding drum, putting it in a pressure vessel and evacuating the pressure vessel once, pure hydrogen gas was introduced and the inside pressure was 2 kg / cm ² . A hydrogen gas atmosphere was used, and a heat treatment was performed at 150 ° C. for 24 hours with a built-in heater. 2 × 10 ⁸ for the image fiber thus obtained
When the transmission image before and after the irradiation with R gamma rays was evaluated, no coloration of the transmission image was observed even after the irradiation, and the transmission characteristics were not deteriorated.

For comparison, an image fiber obtained by performing only heat treatment in a hydrogen atmosphere under the same conditions without irradiating γ-rays with cobalt-60 was similarly 2 × 10 ^8.
When γ-ray irradiation of R was performed and the transmitted image was evaluated,
Coloring was observed, and transmission characteristics were deteriorated. Further, when the γ-ray irradiation dose for evaluation was lowered to 10 ⁶ R, coloring was not recognized in the transmitted image. As is clear from these results, it can be seen that the radiation resistance is remarkably improved by heating in a hydrogen atmosphere after γ-ray irradiation.

(Example 2) First, an image fiber having a coating made of an ultraviolet curable resin was manufactured in the same manner as in Example 1 and wound on a winding drum. Then, this product was placed in a similar pressure vessel, and the hydrogen pressure was 2 kg / cm ² ,
After treatment at a temperature of 150 ° C. for 24 hours, γ-ray irradiation with cobalt-60 was carried out. Next, this was further subjected to hydrogen pressure of 2 kg / cm ² , temperature of 150 ° C.,
A second heat treatment in a hydrogen atmosphere was performed under the condition of a time of 24 hours to obtain a desired radiation resistant image fiber. This product was irradiated with 10 ⁸ R γ-rays, but no deterioration in image transmission characteristics was observed.

[0017]

As described above, according to the method of manufacturing the radiation resistant image fiber of the present invention, the image fiber base material is melt-spun, and the obtained image fiber is irradiated with γ rays and then heated in a hydrogen atmosphere. Therefore, a product having extremely excellent radiation resistance can be manufactured. In particular,
When the spinning of the image fiber and the γ-ray irradiation are performed in tandem, the work efficiency is improved and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an apparatus for carrying out the manufacturing method of the present invention.

FIG. 2 is a schematic sectional view showing an example of an image fiber.

[Explanation of symbols]

11 ... Image fiber base material, 12 ... Heater, 13 ... Image fiber, 14 ... Resin coating die, 15 ... UV cross-linking cylinder, 16 ... Irradiation chamber, 17 ... Radiation source, 18 ... Winding drum

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Tamanuma 1440 Rokuzaki, Sakura City, Chiba Prefecture, Sakura Factory, Fujikura Cable Co., Ltd. (72) Kazuo Sanada, 1440, Rokuzaki, Sakura City, Chiba, Fujikura Cable Company, Ltd.

Claims (3)

[Claims] 1. A method of producing a radiation resistant image fiber, which comprises melt-spinning an image fiber base material, irradiating the obtained image fiber with γ-rays, and then heating in a hydrogen atmosphere. 2. The method for producing a radiation-resistant image fiber according to claim 1, wherein γ-rays are continuously irradiated following the melt spinning. 3. The method for producing a radiation-resistant image fiber according to claim 1, wherein the image fiber after melt spinning is once wound up, and then γ-rays are irradiated on the image fiber.