Objectives  This study focuses on the sealing performance of lifting hatches applied to nuclear power plants under accidental working conditions.

Methods An experimental setup is built to achieve the quantitative measurement of steam micro-leakage. In this device, saturated steam at 0.66 MPa is charged into a pressurized chamber to simulate accident conditions, the leaking steam is collected through a collection chamber with an insulation layer, and no condensation occurs. The changes in temperature, humidity and pressure in the collection chamber are monitored in real time to estimate the steam leakage rate.

Results The experimental results show that the steam leakage rates of the lifting hatch models with 1.5 mm and 3.0 mm composite gaskets are 13.93 g/24h and 11.91 g/24h respectively, both meeting the low leakage design requirements, with the 3.0 mm gasket providing superior sealing performance. An analysis of the dry air and steam measurements with the same gasket and at the same pressure shows that the sealing coefficients nd⁴ obtained for both are very close, which verifies the accuracy of the experimental device for steam microleakage measurements.

Conclusions The proposed steam microleakage measurement method can be extended to various sealing structures and pressure systems, and provides a new measurement idea for evaluating the sealability of stack chambers under accident conditions.