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

https://doi.org/10.1109/TDEI.2015.004880

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).

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

https://doi.org/10.1109/TDEI.2013.6678859

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.

Product analysis for polyethylene degradation by radiation and thermal ageing

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

Radiation Physics and Chemistry, 82, p.69 - 73, 2013/01

https://doi.org/10.1016/j.radphyschem.2012.08.009

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.

Mechanism of antioxidant interaction on polymer oxidation by thermal and radiation ageing

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

Radiation Physics and Chemistry, 81(11), p.1747 - 1751, 2012/11

https://doi.org/10.1016/j.radphyschem.2012.06.011

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.

Ageing research of cable insulation materials

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.

Degradation mechanisms of cable insulation materials during radiation-thermal ageing in radiation environment

Seguchi, Tadao*; Tamura, Kiyotoshi; Oshima, Takeshi; Shimada, Akihiko; Kudo, Hisaaki*

Radiation Physics and Chemistry, 80(2), p.268 - 273, 2011/02

https://doi.org/10.1016/j.radphyschem.2010.07.045

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.

Radiation resistance of polymer materials; Degradation evaluation by accelerated testing for application condition

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.

Gas evolution of polyethylene by radiolysis and the application to dosimeter

Haruyama, Yasuyuki; Sunaga, Hiromi; Arakawa, Kazuo; Seguchi, Tadao

JAERI-Tech 2002-084, 105 Pages, 2002/11

JAERI-Tech-2002-084.pdf:2.01MB

no abstracts in English

Fine SiC fiber synthesized from organosilicon polymers; Relationship between spinning temperature and melt viscosity of precursor polymers

Idesaki, Akira; Narisawa, Masaki*; Okamura, Kiyohito*; Sugimoto, Masaki; Tanaka, Shigeru; Morita, Yosuke; Seguchi, Tadao; Ito, Masayoshi*

Journal of Materials Science, 36(23), p.5565 - 5569, 2001/12

https://doi.org/10.1023/A:1012549228826

A very fine silicon carbide (SiC) fiber with diameter of 6 m, about a half of that of a commercially available SiC fiber, was synthesized from a polymer blend of polycarbosilane (PCS) and polyvinylsilane (PVS). The fine SiC fiber was obtained by optimizing the composition and the spinning temperature of PCS-PVS polymer blends. In order to determine these optimum conditions, the relationship between temperature and melt viscosities of the polymer blends was investigated. As a result, it was found that the optimum spinning temperature range was within a temperature range where the melt viscosity is 5-10Pas. Moreover, by blending PVS with PCS, the spinning temperature of the polymer blends was lowered, the spinnability of polymer system was improved, and finer polymer fiber was obtained compared with PCS. The optimum content of PVS in the polymer blend was 15-20wt%.

Recovery system for uranium from seawater with fibrous adsorbent and its preliminary cost estimation

Sugo, Takanobu; Tamada, Masao; Seguchi, Tadao; Shimizu, Takao*; Uotani, Masaki*; Kashima, Ryoichi*

Nihon Genshiryoku Gakkai-Shi, 43(10), p.1010 - 1016, 2001/10

https://doi.org/10.3327/jaesj.43.1010

The cost of uranium recovered from seawater was estimated by using the amidoxime adsorbent of polymer fibers synthesized by radiation modification, and the technical problems in the recovery system were extracted. The cost of adsorbent materials, storage in seawater for uranium absorption, and the uranium detachment from the adsorbent was estimated respectively in three different systems of the storage in seawater as a buoy, floating body, and chain binding system. The recovery cost of uranium from seawater was estimated to be 810 times of that from mine uranium. More than 80% of the total cost was occupied by the cost for storage in seawater, which is owing to a weight of metal cage for the holding of adsorbents. The cost can be attained to half by the reduction of the weight to 1/4. One of facing research subject is the improvement of adsorbent ability, since the cost directly depends on the adsorbent performance.