Preliminary results of electric insulation void content growth from simulated exposure to a nuclear power plant´s high energy line break event

A need exists to confirm the remaining life of electric cable used in nuclear power stations. Remaining life must include margins for surviving the potential harsh environment effects of a design basis event (DBE) after up to 60 years of normal operation. Typically a DBE would be a postulated break in the largest high temperature pressurized line leading to elevated temperatures (accelerated aging conditions) in the surrounding environment. Previous research has shown that void content within polyolefin electric insulation grows during normal thermal aging and that oxygen diffusion plays a role in this growth. Under accelerated aging conditions, oxygen diffusion is limited reducing chemical reaction rates, and potentially affecting the aging process. This paper discusses preliminary experimental results indicative of accelerated aging for three commonly used polyolefin materials. Each sample was re-examined after thermal annealing for 17 hours at 120 C. Results indicate the void content increased dramatically from the pre-aged sample values