A Practical Research On Bonnet Sealing Of The Dedicated PZR Valves At High Temperature In Nuclear Power Plants

After the Fukushima disaster which was triggered by a disastrous earthquake and tsunami that struck Japan in March 2011.The National Energy Administration organized a security technology research and development program. In order to further improve the safety level and the ability to deal with the extreme disaster of China’s nuclear power units in operation and under construction. The dedicated PZR valve is one of the important equipment in this project. The requirements of the valve can be achieved without any external leakage at 650℃. The valve bonnet seal design is one of the most important in valve design. Therefore, it has important engineering application value to carry out the research about valve bonnet sealing structure at ultra-high temperature.In this paper, the required sealing force of the new gasket in the pressure-sealed bonnet on the design pressure is calculated in according with Elastic-plastic mechanics theory. The bending stress and shear stress of the supporting ring and ring parts are checked in according with design pressure and the sealing force of the gasket, the stress of the supporting ring and the ring is less than the allowable stress value of the material at design temperature. According to the sealing force of the gasket, the minimum diameter of pre-tightening bolt is 11.9mm, selects size of the bolt is 8 ×M16.Using ANSYS software to carry out the finite element structural analysis, which simulate and calculate the stress, temperature field and thermal deformation of the pressure-seal bonnet under different working conditions. The stress strength of the valve body, bonnet in 1.5 times the design pressure, pipeline load and 4g seismic load in three directions are less than the material allowable stress intensity by simulation. A general thermal stress value of each part is less than 1 time of allowable stress intensity at 360℃ by thermal stress analysis in the direction of the wall thickness of the valve body, bonnet and the ring at 360℃. The absolute deformation values of the radial and axial directions between the valve body and the ring are 0.892 mm and 1.381 mm, the absolute deformation values of the radial between bonnet and the valve body is 0.72 mm at 650℃ by simulation.The new pressure-sealed bonnet structure was carried out three times temperature and pressure cycle tests. At 360℃, 17.5MPa, 650℃, 1.9MPa, the leakage of the bonnet is zero. As well as after the test, at room temperature, 17.5MPa, the leakage is zero. All parts were disassembly after test, the machined surface of the body and bonnet, no scratch and other damage.Through the simulation test, the new bonnet structure without any leakage, sealing performance is excellent. It can meet sealing performance requirements of the dedicated PZR valve in nuclear power plants.