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Journal Articles

Degradation of cable insulation material by accelerated thermal radiation combined ageing

Seguchi, Tadao*; Tamura, Kiyotoshi*; Kudo, Hisaaki*; Shimada, Akihiko; Sugimoto, Masaki

IEEE Transactions on Dielectrics and Electrical Insulation, 22(6), p.3197 - 3206, 2015/12

 Times Cited Count:27 Percentile:76.56(Engineering, Electrical & Electronic)

The degradation of ethylene propylene rubber (EPR) sheets as a cable insulation material for nuclear power plants (NPP) was studied by accelerated thermal ageing, radiation ageing and thermal - radiation combined ageing. The oxidation of EPR proceeded with ageing and the decay of mechanical property was closely related to the content of oxidation products. The antioxidant as a stabilizer in EPR was effective for the thermal oxidation, but not for the radiation oxidation. For the thermal and radiation combined oxidation, the mechanical property and the content of oxidation products were different among the treatment sequences due to the decay of antioxidant. The lifetime of EPR cable is closely related to the remaining content of antioxidant, and the lifetime evaluation would be recommended by the reverse sequential combination (thermal ageing after radiation ageing).

Journal Articles

Degradation mechanisms of Silicone Rubber (SiR) by accelerated ageing for cables of nuclear power plant

Shimada, Akihiko; Sugimoto, Masaki; Kudo, Hisaaki*; Tamura, Kiyotoshi*; Seguchi, Tadao*

IEEE Transactions on Dielectrics and Electrical Insulation, 21(1), p.16 - 23, 2014/02

The thermal and radiation ageing behaviors and degradation mechanisms of SiR for the cable insulation of nuclear power plants were studied. The thermal ageing and radiation ageing in air were conducted up to 235$$^{circ}$$C and 195$$^{circ}$$C, respectively. The dose rate of radiation ageing is 1 kGy/h. Thermal ageing in vacuum as well as in air was also conducted. The degraded SiR is evaluated by tensile test, gel fraction measurement, swelling ratio measurement and weight measurement, and then the results are analyzed. It is appeared that the radiation degradation of SiR at high temperature is much more severe than that of SiR at low temperature at the same dose. Focusing on the molecular structure, it is supposed that crosslinking reagents which are included in SiR are removed, oxygen atom is attached instead of the reagents and new crosslinking is foamed. Their behaviors are different from the polymer of hydrocarbon.

Journal Articles

Degradation distribution in insulation materials of cables by accelerated thermal and radiation ageing

Shimada, Akihiko; Sugimoto, Masaki; Kudo, Hisaaki*; Tamura, Kiyotoshi*; Seguchi, Tadao*

IEEE Transactions on Dielectrics and Electrical Insulation, 20(6), p.2107 - 2116, 2013/12

 Times Cited Count:38 Percentile:82.79(Engineering, Electrical & Electronic)

The degradation of cables by the accelerated thermal and radiation ageing for nuclear power plant was studied. The thermal oxidation of crosslinked polyethylene (XLPE) as a cable insulation showed the heterogeneous features along the depth of sheet specimens. The degree of oxidation was closely related to the distribution of antioxidant content due to the decay of antioxidant content by the evaporation and radiation decomposition during accelerated ageing. The specific relations were observed between the tensile properties and the yield of oxidation products and also between the oxidation products and antioxidant content in XLPE specimens. The yields and the content and their distribution were detected by FTIR. The oxidation of XLPE containing antioxidant of enough content proceeded proportionally with ageing time or radiation dose at any ageing conditions. When the antioxidant content decreased less than a limited content by thermal and/or radiation ageing, the oxidation rate by thermal ageing increased sharply with ageing time. Therefore, the oxidation at surface of XLPE was much accelerated when the antioxidant decreased to result the heterogeneous oxidation. The mechanical properties depend closely on the degree of oxidation at the surface. The behavior of oxidation was also affected by the types of antioxidant.

Journal Articles

Radiation ageing technique for cable life evaluation of nuclear power plant

Shimada, Akihiko; Sugimoto, Masaki; Kudo, Hisaaki*; Tamura, Kiyotoshi; Seguchi, Tadao*

IEEE Transactions on Dielectrics and Electrical Insulation, 19(5), p.1768 - 1773, 2012/10

 Times Cited Count:14 Percentile:59.46(Engineering, Electrical & Electronic)

The life of cables installed in nuclear power plant was evaluated by the accelerated ageing tests of thermal and radiation degradation. For radiation degradation, the dose rate was the important points, because the oxidation distribution in the insulation was much affected by dose rate due to oxygen penetration limitation during irradiation. The oxidation distribution was observed by FTIR for crosslinked polyethylene (XLPE) and ethylene propylene rubber (EPR) of cable insulation degraded at various irradiation conditions and compared with the mechanical degradation. The oxidation profile was almost same between a low dose rate at room temperature and a high dose rate at elevated temperature (100 $$^{circ}$$C), and the degradation was same for both irradiations. By increasing the irradiation temperature the oxygen penetration rate increased exponentially and the thermal degradation during irradiation was negligible at around 100 $$^{circ}$$C. Therefore, the dose rate could be increased by 15 times by irradiation at 100 $$^{circ}$$C instead of the irradiation at room temperature for the adequate oxidation throughout insulation. The experimental result was coincident with the theoretical analysis.

Journal Articles

Characteristics of voltage holding capability in multi-stage large electrostatic accelerator for fusion application

Kobayashi, Kaoru; Hanada, Masaya; Akino, Noboru; Sasaki, Shunichi; Ikeda, Yoshitaka; Takahashi, Masahiro*; Yamano, Yasushi*; Kobayashi, Shinichi*; Grisham, L. R.*

IEEE Transactions on Dielectrics and Electrical Insulation, 16(3), p.871 - 875, 2009/06

 Times Cited Count:1 Percentile:12.19(Engineering, Electrical & Electronic)

Voltage holding capability of a 500kV, 22A three-stage electrostatic accelerator, where large-area grids of 0.28 m$$^{2}$$ and large FRP insulators of 1.8 m in diameter are used, was examined. High voltage was independently applied to each acceleration stage, where the voltage holding capabilities of 130 kV were obtained. To identify whether the breakdowns occur in the gaps between the grids or the FRP insulators, high voltages were applied to the accelerator with and without the grids. Breakdown voltages without grids, i.e., the FRP insulator itself reached 170 kV of design value for each stage. These results show that the breakdown voltage of the accelerator was mainly determined by the gaps between the large-area grids. In this paper, the influence of non-uniform electric field and multi-stage grids on the voltage holding capabilities was also discussed.

Journal Articles

Correlation between voltage holding capability and light emission in a 500 keV electrostatic accelerator utilized for fusion application

Hanada, Masaya; Ikeda, Yoshitaka; Kamada, Masaki; Kikuchi, Katsumi; Komata, Masao; Mogaki, Kazuhiko; Umeda, Naotaka; Usui, Katsutomi; Grisham, L. R.*; Kobayashi, Shinichi*

IEEE Transactions on Dielectrics and Electrical Insulation, 14(3), p.572 - 576, 2007/06

 Times Cited Count:5 Percentile:33.84(Engineering, Electrical & Electronic)

Voltage holding capability of a 500 keV 22 A negative ion accelerator for JT-60U was experimentally examined. Voltage holding capability was strongly correlated with intensity of the light emitted inside the accelerator by applying the acceleration voltage. Namely, stable voltage holding was realized when the light emission was well suppressed. To examine the origin of the light emission, the correlation between the light intensity and the dark current was measured. The light intensity was linearly varied with the dark current. Further, it was indicated from the direction of the dark current that electrons were emitted from cathode grids by applying the acceleration voltage. In addition, the spectroscopy measurement of the light showed that the light had a broad peak at 420 nm. No particular spectra of hydrogen, oxygen and carbon have been observed. Therefore, the light emission seemed to be originated by electron excitation of FRP itself. From these results, it was thought that the voltage holding capability of the JT-60U negative ion accelerator could be improved by suppressing the electron emission from the cathode grids.

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