Changes in chemical structure and mechanical properties of cross-linked polyethylene aged under simulated severe accident conditions of a nuclear power plant

Sheets of cross-linked polyethylene (XLPE), which is believed to be the same as that for electrical insulation in safety-related cables in nuclear power plants, were aged under simulated severe accident conditions. Infrared absorption spectroscopy, indenter modulus measurement, and tensile tests were conducted to investigate the correlation between the aging-induced changes in chemical structure and those in the mechanical properties of XLPE. As a result, it has become clear that XLPE is oxidized to form carbonyl groups and becomes slightly brittle by the gamma-irradiation at 100°C. The gamma-irradiation at room temperature scarcely changes the chemical structure and softness. Instead, such gamma-irradiation apparently slows down the progress of embrittlement induced by the subsequent steam exposure at 220°C due to the presence of cross-linked structures.