by Y. Ohki Development of RadiationResistant Cables With increasing public concerns for environmental protection, there has recently been a trend toward reducing the use of substances with heavy environmental burdens. This is also the case in the manufacture of electric cables. Namely, materials that are not environmentally friendly, such as halogens, are to be excluded from cable materials. On the other hand, to promote basic science, many new facilities, such as high-energy physics laboratories that emit high dose-rate radiation, are now being built. Therefore, cables used for electric power equipment and instruments in such facilities should have good radiation resistance. To tackle these two issues, the development of a new halogen-free flame-retardant insulating material for cables, with superior radiation resistance and a long life, has been anticipated. In the present short article, two such kinds of cables, recently developed by Fujikura, Tokyo, are introduced. The first one that was introduced is a halogen-free radiation-resistant cable with a new radiation-resistant sheath developed in cooperation with the Japan Atomic Energy Agency. The new sheath material is polyolefin resin, to which several kinds of radiation-resistant stabilizers or visible- toultraviolet light absorbers are added. The material was irradiated with 60Co γ rays at a dose rate of 5 kGy/h up to a total exposure
Figure 1. Relation between elongation-at-break and radiation dose. Conventional sheath material ------------------------- Developed material of 2.5 MGy. Figure 1 compares the relation between elongation-at-break and radiation dose obtained for the new sheath material with that obtained for a conventional sheath material. The conventional material without the radiation resistant stabilizer became heavily deteriorated by the irradiation of 0.5 MGy, whereas the new material with the stabilizer seems usable up to 2.5 MGy. Further, a cable manufactured with the developed sheath material was irradiated up to 2.5 MGy and subjected to a bending test, in which the cable was bent to a diameter 4 times as large as the cable outer diameter, and to a vertical tray flame test according to the IEEE Std. 383. The cable after the irradiation of 2.5 MGy passed the flame test as shown in Figure 2, exhibiting a superior flame-retardant characteristic. By using the developed sheath material, Fujikura is now producing cables with a maximum permissible dose of 2.5 MGy. This value is 25 times as high as the permissible dose, 0.1 MGy, of the conventional halogen-free flame-retardant cables produced by Fujikura. A series of the developed cables with code names beginning by RH-2.5M were delivered to an advanced experimental facility in the Japan Proton Accelerator Research Complex (J-PARC)
at the Tokai Research and Development Center of the Japan Atomic Energy Agency shown in Figure 3. Fujikura, has also developed a new radiation resistant PEEK (polyether-etherketone) insulated cable together with IHI Corporation and Japan Atomic Energy Agency, which can be used in a very harsh radiation environment. At several locations in the J-PARC facility, the radiation dose rate is very high. Therefore, an even better radiation-resistant performance with tolerance to a total dose up to roughly 10 MGy is required. Under such high-level radiation, hardening or cracking of the
Figure 2. The developed radiationresistant halogen-free cable during the IEEE Std. 383 vertical tray flame test.
IEEE Electrical Insulation Magazine
Figure 3. The radiation-resistant PEEK insulated cable installed to a very harsh radiation environment in a J-PARC facility. Figure 4. A bird’s-eye view of the J-PARC Facility, provided by courtesy of J-PARC Center. cable constituent materials may occur, threatening the insulation performance. Fujikura has developed a cable that can cope with these issues, by selecting PEEK, a polymer well-known for its excellent 979-Gf Member Ad 7x4.75
radiation resistance as an insulating material, and PEEK tapes and heat-resistant aramid fiber as other constituents. Figure 4 shows the developed PEEK-insulated cable, which was installed successfully 3:10 PM
to a very harsh radiation environment in a research facility of J-PARC. This article was written with the help of Dr. T. Shinmoto of Fujikura Ltd.
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