Radiation ageing technique for cable life evaluation of nuclear power plant

The accelerated ageing of cables for nuclear power plant was studied for the life evaluation in the environmental conditions. For the accelerated radiation ageing, the dose rate is the important point, because the oxidation profile in the insulation is much affected by dose rate due to oxygen diffusion limitation during irradiation. The oxidation profile 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 profiles with low dose rate at room temperature and that with high dose rate at elevated temperature (100°C) were very much alike and the mechanical degradations of both irradiations were equal. By increasing the irradiation temperature the oxygen diffusion rate increased exponentially with temperature and the degradation by thermal during irradiation for several hundred hours was very little at around 100°C. Therefore, the dose rate can be increased by 15 times by irradiation at 100°C instead of the irradiation at room temperature for the adequate oxidation throughout the insulation. The experimental result was coincident with the theoretical analysis.