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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：28 Percentile：76.71(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).
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
C and 195C, 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.
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：39 Percentile：82.85(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.
Sugimoto, Masaki; Shimada, Akihiko; Kudo, Hisaaki*; Tamura, Kiyotoshi; Seguchi, Tadao*
Radiation Physics and Chemistry, 82, p.69 - 73, 2013/01
Times Cited Count：61 Percentile：97.76(Chemistry, Physical)The oxidation products formed by thermal and radiation ageing of crosslinked polyethylene for cable insulation were analyzed by FTIR-ATR spectrometry. The most of products were composed of carboxylic acid, carboxylic ester, and carboxylic anhydride. The carboxylic acid was the primal product, and the others were the secondary products by the thermal reaction of carboxylic acids. The carboxylic acid as the primal oxidation product supports the proposed new oxidation mechanisms that the main chain scission should occur directly by oxidation of polyethylene radicals.
Seguchi, Tadao*; Tamura, Kiyotoshi*; Watashi, Katsumi; Suzuki, Masahide; Shimada, Akihiko; Sugimoto, Masaki; Idesaki, Akira; Yoshikawa, Masahito; Oshima, Takeshi; Kudo, Hisaaki*
JAEA-Research 2012-029, 158 Pages, 2012/12
JAEA-Research-2012-029.pdf:9.4MB
The degradation mechanisms of ethylene-propylene rubber (EPR), crosslinked polyethylene (XLPE), polyvinylchloride (PVC), and silicone rubber (SiR) as the cable insulation materials were investigated for the cable ageing research of the nuclear power plant. The materials as same insulations for the practical cable (practical formulation) and as the model formulation containing specific additive were selected. They were exposed to the accelerated radiation and thermal environments. The mechanical properties, the crosslinking and chain scission, and the distribution of antioxidant and of oxidative products were measured and analyzed.
Seguchi, Tadao*; Tamura, Kiyotoshi; Shimada, Akihiko; Sugimoto, Masaki; Kudo, Hisaaki*
Radiation Physics and Chemistry, 81(11), p.1747 - 1751, 2012/11
Times Cited Count：44 Percentile：94.85(Chemistry, Physical)The mechanism of polymer oxidation by radiation and thermal ageing was investigated for the life evaluation of cables installed in radiation environments. The antioxidant as a stabilizer was much effective for thermal oxidation with a small content in polymers, but was not effective for radiation oxidation. The ionizing radiation induced the oxidation to result chain scission even at low temperature, because the free radicals were produced and the antioxidant could not stop the oxidation of radicals with the chain scission. A new mechanism of antioxidant effect for polymer oxidation was proposed. The effect of antioxidant was not the termination of free radicals in polymer chains such as peroxy radicals, but was the depression of initial radical formation in polymer chains by thermal activation. The antioxidant molecule was assumed to delocalize the activated energy in polymer chains by Boltzmann statics (distribution) to result decrease the probability of radical formation at a given temperature. The interaction distance (delocalization area) by one antioxidant molecule was estimated to be 5-10 nm in polymer matrix, though the value would depend on the chemical structure of antioxidant.
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：59.03(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 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 C. Therefore, the dose rate could be increased by 15 times by irradiation at 100 C instead of the irradiation at room temperature for the adequate oxidation throughout insulation. The experimental result was coincident with the theoretical analysis.
Seguchi, Tadao*; Tamura, Kiyotoshi; Kudo, Hisaaki*; Shimada, Akihiko; Sugimoto, Masaki; Idesaki, Akira; Oshima, Takeshi; Yoshikawa, Masahito
JAEA-Review 2012-027, 46 Pages, 2012/08
JAEA-Review-2012-027.pdf:5.87MB
The research on cable degradation mechanisms was conducted for 5 years in 2006 - 2010 as the project research of plant life management for nuclear power plant by NISA (Nuclear and Industrial Safety Agency) of METI (Ministry of Economy, Trade, and Industry). At the finish of above research, the degradation mechanisms were reviewed on the analysis of many reports on cable degradation. The reports published after 1970 were mainly surveyed and the facts or data containing the experimental accuracy were selected. The verified facts, the reasonable interpretation of the facts, unresolved aspects were checked on the view points of recent techniques or analysis, and proposed the new model of degradation mechanisms was proposed.
Shimada, Akihiko; Kudo, Hisaaki*; Idesaki, Akira; Sugimoto, Masaki; Yoshikawa, Masahito; Tamura, Kiyotoshi; Seguchi, Tadao*
Proceedings of 12th International Conference on Radiation Curing in Asia (RadTech Asia 2011) (Internet), p.244 - 247, 2011/06
Seguchi, Tadao*; Tamura, Kiyotoshi; Oshima, Takeshi; Shimada, Akihiko; Kudo, Hisaaki*
Radiation Physics and Chemistry, 80(2), p.268 - 273, 2011/02
Times Cited Count：63 Percentile：97.53(Chemistry, Physical)The cables applied in radiation facility such as a nuclear power plant degrade by radiation and thermal combined ageing. The degradation of polymers for cable insulation is induced by oxidation, and the oxidation is accelerated by synergism of radiation and thermal oxidation. The degradation mechanisms were studied at accelerated degradation for various cable insulation materials. The distribution of degradation in film samples was investigated with various techniques. It was found that the antioxidant agent for stabilizer of insulation materials is closely related to the synergism. With progress of ageing, the concentration of effective antioxidant decreases by radiation decomposition and also by evaporation in thermal ageing. When the concentration of antioxidant is reduced to a limited value, the thermal oxidation is progressing.
Shimada, Akihiko; Kudo, Hisaaki*; Idesaki, Akira; Oshima, Takeshi; Tamura, Kiyotoshi; Seguchi, Tadao*
Proceedings of International Conference on Condition Monitoring and Diagnosis 2010 (CMD 2010), Vol.2, p.705 - 708, 2010/09
The lifetime evaluation of cable insulation used in nuclear power plants is very important for their safety running. In the present, the evaluation of cable lifetime is performed under the higher dose rate of radiation and elevated temperatures compared to actual conditions. In that case, we need to select the reasonable dose rate. One of the important points is the homogeneous oxidation throughout insulation polymer materials during irradiation for the equivalent oxidation with the real ageing condition. The oxidation depth of polymer material depends on the dose rate and oxygen diffusion coefficient into polymer material. Then, the dose rate could be increased if the diffusion coefficient was increased by increasing the irradiation temperature. The relations between dose rate and irradiation temperature were studied on XLPE, EPR, PVC and SiR for cable insulation. These materials are irradiated with cobalt 60 
-rays at dose rates up to 1 kGy/h under elevated temperature. The irradiation effects were analyzed by tensile test, change of swelling ratio and gel fraction, SEM-EDS, and FT-IR.
Seguchi, Tadao*; Sorimachi, Masami*; Tamura, Kiyotoshi
JAEA-Data/Code 2009-018, 123 Pages, 2010/02
JAEA-Data-Code-2009-018.pdf:23.94MB
The radiation resistance of 25 type polymer materials as plastics and rubbers applied in practical environments was evaluated by the accelerated testing of -ray irradiation under oxygen pressure, and compared with the radiation resistance determined from the traditional testing by irradiation with a high dose rate in air. The polymer materials were formulated to be similar or equivalent to practical materials, and the most of formulation (chemical compounds and quantities) were disclosed. For all materials, the tensile properties (elongation at break, ultimate strength, 100% or 200% modulus), electric resistivity, gel-fraction, and density were measured after irradiation in oxidation conditions and non-oxidation conditions. The data of relations between each properties and total dose at various conditions were compiled, and the relations among the changes of mechanical properties, electrical properties, and radiation induced chemical reactions were discussed.
Idesaki, Akira; Seguchi, Tadao*; Tamura, Kiyotoshi; Oshima, Takeshi; Shimada, Akihiko; Kudo, Hisaaki*
no journal, ,
The degradation of polyvinylchloride (PVC) of cable insulation was investigated by accelerated radiation and thermal ageing. The sheets of PVC as same formulation as cables were subjected to thermal ageing at temperature range 100-135C and/or to radiation ageing by Co-60 -rays at a dose rate of 1kGy/h in air. The degradation was evaluated by the tensile test and by the weight change. The relations between elongation at break and change of weight by loss of plasticizer were analyzed. At higher temperature, the plasticizer evaporates to cause the decay of tensile properties.
Shimada, Akihiko; Seguchi, Tadao*; Tamura, Kiyotoshi; Oshima, Takeshi; Idesaki, Akira; Kudo, Hisaaki*
no journal, ,
Silicone rubber (SiR) sheets with different formulation were examined on the two points, specimen's thickness and thermal and radiation combined accelerated ageing. The 0.5 and 2 mm thick sheets were aged by thermal at up to 235C and Co-60 rays radiation with 1 kGy/h up to 800 kGy. The degradation was measured by tensile testing and gel fraction and swelling experiments. For check the distribution of degradation in depth of sheet, the 2 mm sheet sample was sliced by 0.3 mm thickness after ageing. The results indicated that the degradation progressed uniformly throughout the 2 mm thick sheet. For the ageing combination, the degradation by three different combinations was examined, that is, (a) simultaneous ageing, (b) thermal and radiation sequential ageing, and (c) radiation and thermal reversed sequential ageing. Elongation at break indicated that the order of degradation mild to severe was reverse sequential, sequential, simultaneous ageing.
Seguchi, Tadao*; Tamura, Kiyotoshi; Shimada, Akihiko; Idesaki, Akira; Oshima, Takeshi; Kudo, Hisaaki*
no journal, ,
no abstracts in English
Shimada, Akihiko; Idesaki, Akira; Oshima, Takeshi; Tamura, Kiyotoshi; Seguchi, Tadao*; Kudo, Hisaaki*
no journal, ,
no abstracts in English
Seguchi, Tadao*; Tamura, Kiyotoshi; Shimada, Akihiko; Idesaki, Akira; Oshima, Takeshi; Kudo, Hisaaki*
no journal, ,
The degradation mechanisms of polymer materials as PE, EPR for cable insulations in a nuclear power plant were studied by accelerated thermal and radiation ageing. The contribution of stabilizers to polymer degradation was investigated by the measurements of oxidation products, content of stabilizers, and also mechanical properties. It was found that an antioxidant among the stabilizers was very effective to decrease the thermal oxidation but less effective to the radiation induced oxidation. The content of the antioxidant decreases by evaporation during thermal ageing and by decomposition with dose during radiation ageing. The new degradation mechanisms in polymer ageing are proposed.
Shimada, Akihiko; Seguchi, Tadao*; Tamura, Kiyotoshi; Oshima, Takeshi; Idesaki, Akira; Kudo, Hisaaki*
no journal, ,
Silicone rubber (SiR) is used widely in cable insulation in nuclear power plants. SiR sheets with different formulation were examined on the two points, specimen's thickness and thermal and radiation combined accelerated ageing. The 0.5 and 2 mm thick sheets were aged by thermal at up to 235C and 
Co rays radiation with 1 kGy/h up to 800 kGy. The degradation was measured by tensile testing and gel fraction and swelling experiments. For check the distribution of degradation in depth of sheet, the 2 mm sheet sample was sliced by 0.3 mm thickness after ageing. The results indicated that the degradation progressed uniformly throughout the 2 mm thick sheet. For the ageing combination, the degradation by three different combinations was examined, that is, (a) simultaneous ageing, (b) thermal and radiation sequential ageing, and (c) radiation and thermal reversed sequential ageing. Elongation at break indicated that the order of degradation mild to severe was reverse sequential, sequential, simultaneous ageing. The study was supported by Nuclear and Industrial Safety Agency (NISA), Japanese Minister of Economy, Trade and Industry (METI).
Idesaki, Akira; Seguchi, Tadao*; Tamura, Kiyotoshi; Oshima, Takeshi; Shimada, Akihiko; Kudo, Hisaaki*
no journal, ,
The degradation of polyvinylchloride (PVC) used in cable insulation in nuclear power plant was investigated by accelerated thermal and radiation ageing. The sheets of PVC as same formulation as cables were subjected to thermal ageing at temperature range 100-135C and/or to radiation ageing by Co -rays at a dose rate of 1 kGy/h in air. The degradation was evaluated by the tensile test and by the weight change. The relations between elongation at break and change of weight by loss of plasticizer were analyzed. At higher temperature, the plasticizer evaporates to cause the decrease of tensile properties. The study was supported by Nuclear and Industrial Safety Agency (NISA), Japanese Minister of Economy, Trade and Industry (METI).
Shimada, Akihiko; Kudo, Hisaaki*; Seguchi, Tadao*; Tamura, Kiyotoshi; Sugimoto, Masaki; Idesaki, Akira; Yoshikawa, Masahito
no journal, ,
no abstracts in English
Seguchi, Tadao*; Tamura, Kiyotoshi*; Kudo, Hisaaki*; Shimada, Akihiko; Sugimoto, Masaki
no journal, ,
The degradation of ethylene propylene rubber (EPR) as the cable insulation material for nuclear power plants (NPP) was studied by the accelerated thermal ageing, radiation ageing and thermal - radiation combined ageing. The oxidation of EPR proceeded with both thermal and radiation and the decay of mechanical property was closely related to the degree of oxidation. The thermal oxidation was much affected by the content of antioxidant in EPR as a stabilizer, that is, the oxidation rate was almost same above a critical content of antioxidant but increased much by the decay less than the critical value. On the other hand, the radiation oxidation rate was scarcely affected by the content of antioxidant. As the antioxidant in EPR evaporates from the material surface during thermal ageing and decomposes with dose by the radiation ageing, so the oxidation distribution in the depth of EPR sheet specimen was changed with reflecting the content of antioxidant above or less than the critical value. In the case of combined oxidation of thermal and radiation ageing, the yield and distribution of oxidation in EPR specimen were different by the sequence of ageing combination. The mechanical properties were well reflected by the yield and distribution of oxidation products. As far as the antioxidant content was held above the critical value, the degradation was almost same among the sequence of thermal and radiation ageing, but when the antioxidant was decayed less than the critical value the degradation was much increased in the reverse sequential ageing. For the qualification testing method of the NPP cables, the reverse sequential combination, radiation then thermal ageing, could be recommended.
