Sensitivity analysis of low-pressure gland seal deformation behavior during vacuuming for a 1000 MW nuclear steam turbine based on thermo-mechanical coupling method

In startup process of steam turbine in nuclear power plant, undue deformation of gland seal (GS) may cause rubbing fault. Due to small gland seal clearance, modern advanced steam turbine requires precise control of gland seal deformation (GSD). In line with the above mentioned situations, firstly, a comparison study to reveal GSD behavior on low pressure (LP) casing of a 1000 MW nuclear steam turbine was carried out in startup process by using thermo-mechanical coupling method. The most serious condition for GSD was found out. Further, sensitivity analysis of GSD was conducted. The influence of back pressure and temperature of GS and bearing on GSD during vacuuming (VA) were researched. Finally, to evaluate the risk of rubbing fault, a formula for predicting the bottom clearance of GS during VA was proposed. The results indicate that, in startup process, the GS moves up significantly during VA. The calculated data are in good agreement with on-site measurements. The temperature rise of exhaust hood, which is influenced by GS temperature, makes the GS to lift up. The GS temperature is the most sensitive factor affecting GSD during VA. Rubbing fault may occur when the temperature of GS reaches 112 °C during VA. The results of this research has been used as a guidance for analyzing and improving operational reliability of steam turbine in nuclear power plants.