Silicone rubber in nuclear power plants: prediction of service lifetime in moist conditions

Silicone rubber is thermally stable and it withstands solar radiation. Silicone rubber is sensitive to moisture at elevated temperatures. This report presents a background to the experimental work required to predict lifetimes of silicon rubber components subjected to moisture at 20 – 50 °C.

By moist ageing of silicone rubber samples at 60 to 100 °C and in neutral water and alkaline water (pH = 13.5; resembling fresh concrete) data are obtained that allows extrapolation and prediction of lifetime at lower temperatures. This report presents a fundamental research part that reveals the kinetics of degradation of the material.

A simpler, less timeconsuming method is also suggested that uses tensile testing at 23 °C to assess fracture strain and its dependence on temperature, relative humidity and pH during ageing. Structural integrity and preserved adhesion to the surrounding materials in a transit joint are important.

The obtained mechanical data can be used to predict lifetimes at lower service temperatures (20 – 50 °C), also focussing on both fracture toughness and adhesion to surrounding materials.