Characterization of long-term evolution of leakage rates of O-ring seals in nuclear power plant under high-temperature and high-pressure conditions

Under accident conditions, the sustained high temperature and high pressure (HTHP) environment within the containment structure poses a threat to the penetration seals. This study integrates finite element analysis of the mechanical properties of O-ring, both hyperelastic and viscoelastic characteristics, and an interfacial leakage model to predict the variation in O-ring leakage rates over time in HTHP environments. A series of leakage test experiments are conducted to validate the predictive model, indicating good agreement between experimental and predicted values. The effects of HTHP on non-aged O-rings (short-term service) are analyzed through mechanical simulations and leakage rate calculations. The results reveal that high temperatures positively and reversibly affect the O-ring seals, with hazardous conditions mainly resulting from over-pressurization. However, during the long-term service of aged O-rings, thermal aging caused by high temperatures significantly influences leakage rates. The thermal aging coupled with high pressure can cause material damage (such as rubber being squeezed out) and functional failures (excessive leakage rates). The long-term leakage rates of O-rings at high temperatures in further investigation exhibits a time–temperature equivalence. The master curve is plotted to derive an equation that describes the relationship between leakage rates, temperature, and time under specific pressure conditions. The equation indicates that the dimensionless leakage rate serves as an indicator of seal degradation and enables the quantitative evaluation of the long-term service life of the O-rings using the maximum allowable leakage rate. These findings are applicable within the range of accidental operating conditions for containment structures, including temperatures up to 160 °C and pressures up to 0.75 MPa.