Thermo-Fluid-Solid Coupling Analysis on Deformation of Steam Isolation Valves During Closing Process

Steam isolation valves are equipped in nuclear steam supply systems to isolate faults quickly under accident conditions. With the development of fourth-generation nuclear power technology, high-temperature, high-pressure and high mass flow working conditions can easily cause damage to the valve. When the gate slides down vertically, the steam collides against the gate and leads to the deformation and stiction of the gate, significantly affecting the closing time of the valve. To assess whether the steam isolation valve can be closed normally during closing process, the fluid-solid-thermal method is used to simulate deformation considering the contact nonlinearities, pressure and temperature load. On this basis, the reasons for deformation in the x and z directions and possible location of stiction are analyzed. Simulation results show that the horizontal fluid force increases linearly as opening degree decreases. The deformation in the x and z directions are affected by fluid force and high-temperature thermal expansion, respectively. Besides, the deformation reasons of the front gate and behind gate are fluid pressure difference along the x and y direction, respectively. The deformation changes little on the guide ribs and behind gate but decreases on the front gate during closing process. Considering the fit clearance, the behind gate is most prone to stiction, and the inclination angle mainly distributes between 0.33 ° ∼ 0.55 °. This work provides a reference value for the stiction mechanism and reliability design of steam isolation valves in nuclear power plants.