Abstract
During the service period of low-voltage nuclear cables, multiple stresses influence the aging of polymeric materials of cables. Thermal and radiation stresses are considered service aging factors in qualification tests, while the standards usually do not prescribe mechanical stress. CSPE/XLPE insulated nuclear cable samples were exposed to thermal and combined thermo-mechanical aging for more than 1200 h at 120 °C. The real and imaginary parts of permittivity were measured in the 200 μHz to 50 mHz range as dielectric properties. The Shore D hardness of the samples was measured to analyze the mechanical characteristics of the cable. To characterize the dielectric spectrum, derived quantities, namely central real and imaginary permittivities and real and imaginary permittivities’ central frequencies were calculated. The change of dielectric spectra did not show a clear trend with aging, but the imaginary permittivity’s central frequency was higher by 0.5 mHz in the case of thermo-mechanically aged samples. The Shore D hardness was also higher on the thermo-mechanically aged samples. These findings show the combined aging has a higher impact on the insulation properties. Hence, involving the mechanical stress in the aging procedure of cable qualification enables the design of more robust cables in a harsh environment.
Highlights
In 2020, the built-in nuclear-generating capacity was 393 GW, and its contribution to electricity generation is expected to increase
Nuclear power will keep its important role in power generation for decades, and the current nuclear power plants’ (NPPs’) designed lifetime is potentially extended to 80 years [2]
In this research, the Shore D hardness was tested as a comparative measurement to investigate the mechanical properties
Summary
In 2020, the built-in nuclear-generating capacity was 393 GW (electrical), and its contribution to electricity generation is expected to increase. Nuclear power will keep its important role in power generation for decades, and the current nuclear power plants’ (NPPs’) designed lifetime is potentially extended to 80 years [2] During this long period, the safe and reliable operation of NPPs in normal service and design basis events (DBEs) require safety-related equipment performance to meet their designed requirements. More the 1000 miles of cable installed typically in a pressurized water reactor (PWR), low-voltage (LV) power cables account for only 15% of the total LV cables deployed in the NPPs [5]. Still, they are highly important as they supply motors and pumps related to nuclear safety. For the LV cables, elevated temperature and radiation could be the major factors, along with the chemical contamination and mechanical stresses in some cases [10,12]
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